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• How to stop a ICMP attack?

  - by cumhur onat

  We are under a heavy icmp flood attack. Tcpdump shows the result below. Altough we have blocked ICMP with iptables tcpdump still prints icmp packets. I've also attached iptables configuration and "top" result. Is there any thing I can do to completely stop icmp packets? [root@server downloads]# tcpdump icmp -v -n -nn tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes 03:02:47.810957 IP (tos 0x0, ttl 49, id 16007, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 124, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.811559 IP (tos 0x0, ttl 49, id 16010, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 52, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.811922 IP (tos 0x0, ttl 49, id 16012, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 122, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.812485 IP (tos 0x0, ttl 49, id 16015, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 126, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.812613 IP (tos 0x0, ttl 49, id 16016, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 122, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.812992 IP (tos 0x0, ttl 49, id 16018, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 122, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.813582 IP (tos 0x0, ttl 49, id 16020, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 52, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.814092 IP (tos 0x0, ttl 49, id 16023, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 120, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.814233 IP (tos 0x0, ttl 49, id 16024, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 120, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.815579 IP (tos 0x0, ttl 49, id 16025, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 50, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.815726 IP (tos 0x0, ttl 49, id 16026, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 IP (tos 0x0, ttl 50, id 31864, offset 0, flags [none], proto: ICMP (1), length: 76) 77.92.136.196 > 94.201.175.188: [|icmp] 03:02:47.815890 IP (tos 0x0, ttl 49, id 16027, offset 0, flags [none], proto: ICMP (1), length: 56) 80.227.64.183 > 77.92.136.196: ICMP redirect 94.201.175.188 to host 80.227.64.129, length 36 iptables configuration: [root@server etc]# iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination ofis tcp -- anywhere anywhere tcp dpt:mysql ofis tcp -- anywhere anywhere tcp dpt:ftp DROP icmp -- anywhere anywhere Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination DROP icmp -- anywhere anywhere Chain ofis (2 references) target prot opt source destination ACCEPT all -- OUR_OFFICE_IP anywhere DROP all -- anywhere anywhere top: top - 03:12:19 up 400 days, 15:43, 3 users, load average: 1.49, 1.67, 2.61 Tasks: 751 total, 3 running, 748 sleeping, 0 stopped, 0 zombie Cpu(s): 8.2%us, 1.0%sy, 0.0%ni, 87.9%id, 2.1%wa, 0.1%hi, 0.7%si, 0.0%st Mem: 32949948k total, 26906844k used, 6043104k free, 4707676k buffers Swap: 10223608k total, 0k used, 10223608k free, 14255584k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 36 root 39 19 0 0 0 R 100.8 0.0 17:03.56 ksoftirqd/11 10552 root 15 0 11408 1460 676 R 5.7 0.0 0:00.04 top 7475 lighttpd 15 0 304m 22m 15m S 3.8 0.1 0:05.37 php-cgi 1294 root 10 -5 0 0 0 S 1.9 0.0 380:54.73 kjournald 3574 root 15 0 631m 11m 5464 S 1.9 0.0 0:00.65 node 7766 lighttpd 16 0 302m 19m 14m S 1.9 0.1 0:05.70 php-cgi 10237 postfix 15 0 52572 2216 1692 S 1.9 0.0 0:00.02 scache 1 root 15 0 10372 680 572 S 0.0 0.0 0:07.99 init 2 root RT -5 0 0 0 S 0.0 0.0 0:16.72 migration/0 3 root 34 19 0 0 0 S 0.0 0.0 0:00.06 ksoftirqd/0 4 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/0 5 root RT -5 0 0 0 S 0.0 0.0 1:10.46 migration/1 6 root 34 19 0 0 0 S 0.0 0.0 0:01.11 ksoftirqd/1 7 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/1 8 root RT -5 0 0 0 S 0.0 0.0 2:36.15 migration/2 9 root 34 19 0 0 0 S 0.0 0.0 0:00.19 ksoftirqd/2 10 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/2 11 root RT -5 0 0 0 S 0.0 0.0 3:48.91 migration/3 12 root 34 19 0 0 0 S 0.0 0.0 0:00.20 ksoftirqd/3 13 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/3 uname -a [root@server etc]# uname -a Linux thisis.oursite.com 2.6.18-238.19.1.el5 #1 SMP Fri Jul 15 07:31:24 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux arp -an [root@server downloads]# arp -an ? (77.92.136.194) at 00:25:90:04:F0:90 [ether] on eth0 ? (192.168.0.2) at 00:25:90:04:F0:91 [ether] on eth1 ? (77.92.136.193) at 00:23:9C:0B:CD:01 [ether] on eth0

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• Block IP Address including ICMP using UFW

  - by dr jimbob

  I prefer ufw to iptables for configuring my software firewall. After reading about this vulnerability also on askubuntu, I decided to block the fixed IP of the control server: 212.7.208.65. I don't think I'm vulnerable to this particular worm (and understand the IP could easily change), but wanted to answer this particular comment about how you would configure a firewall to block it. I planned on using: # sudo ufw deny to 212.7.208.65 # sudo ufw deny from 212.7.208.65 However as a test that the rules were working, I tried pinging after I setup the rules and saw that my default ufw settings let ICMP through even from an IP address set to REJECT or DENY. # ping 212.7.208.65 PING 212.7.208.65 (212.7.208.65) 56(84) bytes of data. 64 bytes from 212.7.208.65: icmp_seq=1 ttl=52 time=79.6 ms ^C --- 212.7.208.65 ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 79.630/79.630/79.630/0.000 ms Now, I'm worried that my ICMP settings are too generous (conceivably this or a future worm could setup an ICMP tunnel to bypass my firewall rules). I believe this is the relevant part of my iptables rules is given below (and even though grep doesn't show it; the rules are associated with the chains shown): # sudo iptables -L -n | grep -E '(INPUT|user-input|before-input|icmp |212.7.208.65)' Chain INPUT (policy DROP) ufw-before-input all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-before-input (1 references) ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 4 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 11 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 12 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 8 ufw-user-input all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-user-input (1 references) DROP all -- 0.0.0.0/0 212.7.208.65 DROP all -- 212.7.208.65 0.0.0.0/0 How should I go about making it so ufw blocks ICMP when I specifically attempt to block an IP address? My /etc/ufw/before.rules has in part: # ok icmp codes -A ufw-before-input -p icmp --icmp-type destination-unreachable -j ACCEPT -A ufw-before-input -p icmp --icmp-type source-quench -j ACCEPT -A ufw-before-input -p icmp --icmp-type time-exceeded -j ACCEPT -A ufw-before-input -p icmp --icmp-type parameter-problem -j ACCEPT -A ufw-before-input -p icmp --icmp-type echo-request -j ACCEPT I'm tried changing ACCEPT above to ufw-user-input: # ok icmp codes -A ufw-before-input -p icmp --icmp-type destination-unreachable -j ufw-user-input -A ufw-before-input -p icmp --icmp-type source-quench -j ufw-user-input -A ufw-before-input -p icmp --icmp-type time-exceeded -j ufw-user-input -A ufw-before-input -p icmp --icmp-type parameter-problem -j ufw-user-input -A ufw-before-input -p icmp --icmp-type echo-request -j ufw-user-input But ufw wouldn't restart after that. I'm not sure why (still troubleshooting) and also not sure if this is sensible? Will there be any negative effects (besides forcing the software firewall to force ICMP through a few more rules)?

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• ICMP Redirect Theory VS. Application

  - by joeqwerty

  I'm trying to watch ICMP redirects in a lab using Cisco Packet Tracer (version 5.3.2) and I'm not seeing them, which leads me to believe that either my lab configuration isn't correct or my understanding of ICMP redirects isn't correct or that Packet Tracer doesn't support/use ICMP redirects. Here's what I believe to be true regarding ICMP redirects: Routers send ICMP redirects when all of these conditions are met: The interface on which the packet comes into the router is the same interface on which the packet gets routed out. The subnet or network of the source IP address is on the same subnet or network of the next-hop IP address of the routed packet. The datagram is not source-routed. The router kernel is configured to send redirects. I have the lab set up in Cisco Packet Tracer as displayed in the image and would expect to see an ICMP redirect from Router1 when pinging from PC1 to PC3. I'm not seeing the ICMP redirect and it looks like Router1 is actually routing all of the packets via Router2. I have IP ICMP debugging enabled on Router1 (and Router2) and I'm not seeing any ICMP redirect activity in either console. I'm also not seeing a route to the PC3 network in the routing table on PC1, which I think confirms that the ICMP redirect is not occurring. I'm using only static routing on Routers 1 and 2. Is my understanding of ICMP redirects incorrect, or is there a problem with my lab configuration or does Packet Tracer not support/use ICMP redirects?

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• Why isn't ICMP routing with iptables nat routing

  - by Scott Forsyth - MVP

  I'm using iptables on Ubuntu server to route a public IP to a private IP. I want to nat all traffic, including 80, 443 and ICMP. However, it appears that ICMP isn't routing. I have a steady ping going to the public IP and it never stops, even with NAT pointing to a bogus IP. Here are the rules that I'm using: iptables -t nat -I PREROUTING -d 206.72.119.76 -j DNAT --to-destination 10.240.5.5 iptables -t nat -I POSTROUTING -s 10.240.5.5 -j SNAT --to-source 206.72.119.76 I tried with rules for ICMP specifically, but no such luck: iptables -t nat -I PREROUTING -d 206.72.119.76 - icmp --icmp-type echo-request -j DNAT --to-destination 10.240.5.5 Any ideas?

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• Prevent Linux from processing incoming ICMP Host unreachable packets

  - by bbc

  I have a test setup with one host on a network (10.1.0.0/16) talking via TCP to another one on another network (10.2.0.0/16) and a gateway in the middle. Sometimes, the TCP connection is lost and while scanning the trace (pcap), I looks like it's because of just one ICMP Host unreachable message sent by the gateway to 10.1.0.1 at some point. 10.1.0.1 then sends a TCP RST to 10.2.0.1. In my opinion, the gateway (pfSense) is broken or not configured correctly but anyway, for testing purposes, I'd like to block this kind of ICMP on the host (10.1.0.1) before it has an influence on my TCP connection (or does it? I'm not even sure). I've tried iptables: iptables -I INPUT -i eth0 -p icmp --icmp-type host-unreachable -j DROP but while it does a good job at preventing userpace applications like ping from receiving these ICMP messages, my TCP connection still comes to an end when the alleged "killer ICMP packet" is sent by the gateway. Am I right about how it is processed? If yes, then what can I do to achieve my goal?

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• xen 4.1 host priodically dropping network packets of domU

  - by Dyutiman Chakraborty

  I have xen 4.1 Host running on a ubuntu 12.04 LTS Server with ip 153.x.x.54. I have setup 2 VMs on it, namely, "dev.mydomain.com" and "web.mydomain.com" with ips 195.X.X.2 and 195.x.x.3 respectively. For network the VMs connect through xendbr0 (xen-bridge), and can accces the network properly. I can also login to the VMs with ssh with no issue. However when I ping any of the VMs, there is a high amount of periodic packet drop. If I the ping the xen host (dom0) there is no packet drop. Following is a output of "tcpdump | grep ICMP" on dOM0 while I was pinging one of the domU tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 05:19:55.682493 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 30, length 64 05:19:56.691144 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 31, length 64 05:19:57.698776 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 32, length 64 05:19:58.706784 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 33, length 64 05:19:59.714751 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 34, length 64 05:20:00.723144 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 35, length 64 05:20:01.730349 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 36, length 64 05:20:02.739017 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 37, length 64 05:20:03.746806 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 38, length 64 05:20:06.770326 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 41, length 64 05:20:07.778801 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 42, length 64 05:20:08.786481 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 43, length 64 05:20:09.794720 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 44, length 64 05:20:10.802395 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 45, length 64 05:20:11.810770 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 46, length 64 05:20:12.818511 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 47, length 64 05:20:13.826817 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 48, length 64 05:20:14.835125 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 49, length 64 05:20:15.842138 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 50, length 64 05:20:18.274072 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 1, length 64 05:20:19.282347 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 2, length 64 05:20:20.290746 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 3, length 64 05:20:21.297910 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 4, length 64 05:20:22.305656 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 5, length 64 05:20:23.314369 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 6, length 64 05:20:24.322055 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 7, length 64 05:20:25.329782 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 8, length 64 05:20:26.338473 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 9, length 64 05:20:27.346411 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 10, length 64 05:20:28.354175 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 11, length 64 05:20:29.361640 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 12, length 64 05:20:30.370026 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 13, length 64 05:20:31.377696 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 14, length 64 05:20:32.386151 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 15, length 64 05:20:33.394118 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 16, length 64 05:20:34.402058 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 17, length 64 05:20:35.409002 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 18, length 64 05:20:36.417692 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 19, length 64 05:20:36.496916 IP6 fe80::3285:a9ff:feec:fc69 > ip6-allnodes: HBH ICMP6, multicast listener querymax resp delay: 1000 addr: ::, length 24 05:20:36.499112 IP6 fe80::21c:c0ff:fe6c:c091 > ff02::1:ff6c:c091: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff6c:c091, length 24 05:20:36.507041 IP6 fe80::227:eff:fe11:fa3f > ff02::1:ff00:2: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:2, length 24 05:20:36.523919 IP6 fe80::21c:c0ff:fe77:6257 > ff02::1:ff77:6257: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff77:6257, length 24 05:20:36.544785 IP6 fe80::54:ff:fe12:ea9a > ff02::1:ff12:ea9a: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff12:ea9a, length 24 05:20:36.581740 IP6 fe80::5604:a6ff:fef1:6da7 > ff02::1:fff1:6da7: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:fff1:6da7, length 24 05:20:36.600103 IP6 fe80::8a8:8aa0:5e18:917a > ff02::1:ff18:917a: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff18:917a, length 24 05:20:36.601989 IP6 fe80::227:eff:fe11:fa3e > ff02::1:ff11:fa3e: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff11:fa3e, length 24 05:20:36.611090 IP6 fe80::dcad:56ff:fe57:3bbe > ff02::1:ff57:3bbe: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff57:3bbe, length 24 05:20:36.660521 IP6 fe80::54:ff:fe02:1d31 > ff02::1:ff00:6: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:6, length 24 05:20:36.698871 IP6 fe80::21e:8cff:feb4:9f89 > ff02::1:ffb4:9f89: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ffb4:9f89, length 24 05:20:36.776548 IP6 fe80::54:ff:fe12:ea9a > ff02::1:ff01:7: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff01:7, length 24 05:20:36.781910 IP6 fe80::54:ff:fe8f:6dd > ff02::1:ff00:3: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:3, length 24 05:20:36.865475 IP6 fe80::21c:c0ff:fe4a:ae9f > ff02::1:ff4a:ae9f: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff4a:ae9f, length 24 05:20:36.908333 IP6 fe80::dcad:45ff:fe90:84db > ff02::1:ff90:84db: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff90:84db, length 24 05:20:36.919653 IP6 fe80::54:ff:fe12:ea9a > ff02::1:ff00:7: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:7, length 24 05:20:36.924276 IP6 fe80::59a2:2a4a:2082:6dee > ff02::1:ff82:6dee: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff82:6dee, length 24 05:20:37.001905 IP6 fe80::54:ff:fe8f:6dd > ff02::1:ff8f:6dd: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff8f:6dd, length 24 05:20:37.042403 IP6 fe80::54:ff:fe95:54f2 > ff02::1:ff95:54f2: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff95:54f2, length 24 05:20:37.090992 IP6 fe80::21c:c0ff:fe77:62ac > ff02::1:ff77:62ac: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff77:62ac, length 24 05:20:37.098118 IP6 fe80::d63d:7eff:fe01:b67f > ff02::1:ff01:b67f: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff01:b67f, length 24 05:20:37.118784 IP6 fe80::54:ff:fe12:ea9a > ff02::202: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::202, length 24 05:20:37.168548 IP6 fe80::54:ff:fe02:1d31 > ff02::1:ff02:1d31: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff02:1d31, length 24 05:20:41.743286 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 1, length 64 05:20:41.743542 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 1, length 64 05:20:42.743859 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 2, length 64 05:20:42.743952 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 2, length 64 05:20:43.745689 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 3, length 64 05:20:43.745777 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 3, length 64 05:20:44.746706 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 4, length 64 05:20:44.746796 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 4, length 64 05:20:45.747986 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 5, length 64 05:20:45.748082 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 5, length 64 05:20:46.749834 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 6, length 64 05:20:46.749920 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 6, length 64 05:20:47.750838 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 7, length 64 05:20:47.751182 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 7, length 64 05:20:48.751909 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 8, length 64 05:20:48.751991 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 8, length 64 05:20:49.752542 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 9, length 64 05:20:49.752620 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 9, length 64 05:20:50.754246 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 10, length 64 05:20:51.753856 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 11, length 64 05:20:52.752868 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 12, length 64 05:20:53.754174 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 13, length 64 05:20:54.753972 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 14, length 64 05:20:55.753814 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 15, length 64 05:20:56.753391 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 16, length 64 05:20:57.753683 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 17, length 64 05:20:58.753487 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 18, length 64 05:20:59.754013 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 19, length 64 05:21:00.753169 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 20, length 64 05:21:01.753757 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 21, length 64 05:21:02.753307 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 22, length 64 05:21:03.753021 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 23, length 64 05:21:04.753628 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 24, length 64 ^C479 packets captured 718 packets received by filter 238 packets dropped by kernel 3 packets dropped by interface You see the ping request is not responed to initially, then for a moment it is replied back and then again no reply. I have tried everything (to the best of my knowledge) to fix this, but can't find any answer Any help will be greatly appreciated Thanks.

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• Process does ICMP port scan on my OSX box and I am afraid my Mac got a virus

  - by Jamgold

  I noticed that my 10.6.6 box has some process sending out ICMP messages to "random" hosts, which concerns me a lot. when doing a tcpdump icmp I see a lot of the following 15:41:14.738328 IP macpro > bzq-109-66-184-49.red.bezeqint.net: ICMP macpro udp port websm unreachable, length 36 15:41:15.110381 IP macpro > 99-110-211-191.lightspeed.sntcca.sbcglobal.net: ICMP macpro udp port 54045 unreachable, length 36 15:41:23.458831 IP macpro > 188.122.242.115: ICMP macpro udp port websm unreachable, length 36 15:41:23.638731 IP macpro > 61.85-200-21.bkkb.no: ICMP macpro udp port websm unreachable, length 36 15:41:27.329981 IP macpro > c-98-234-88-192.hsd1.ca.comcast.net: ICMP macpro udp port 54045 unreachable, length 36 15:41:29.349586 IP macpro > c-98-234-88-192.hsd1.ca.comcast.net: ICMP macpro udp port 54045 unreachable, length 36 I got suspicious when my router notified me about a lot of ICMP messages that don't get a response [INFO] Mon Jan 10 16:31:47 2011 Blocked outgoing ICMP packet (ICMP type 3) from 192.168.1.189 to 212.25.57.90 Does anyone know how to trace which process (or worse kernel module) might be responsible for this? I rebooted and logged in with a virgin user account and tcpdump showed the same results. Any dtrace magic welcome.

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• Why not block ICMP?

  - by Agvorth

  I think I almost have my iptables setup complete on my CentOS 5.3 system. Here is my script... # Establish a clean slate iptables -P INPUT ACCEPT iptables -P FORWARD ACCEPT iptables -P OUTPUT ACCEPT iptables -F # Flush all rules iptables -X # Delete all chains # Disable routing. Drop packets if they reach the end of the chain. iptables -P FORWARD DROP # Drop all packets with a bad state iptables -A INPUT -m state --state INVALID -j DROP # Accept any packets that have something to do with ones we've sent on outbound iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT # Accept any packets coming or going on localhost (this can be very important) iptables -A INPUT -i lo -j ACCEPT # Accept ICMP iptables -A INPUT -p icmp -j ACCEPT # Allow ssh iptables -A INPUT -p tcp --dport 22 -j ACCEPT # Allow httpd iptables -A INPUT -p tcp --dport 80 -j ACCEPT # Allow SSL iptables -A INPUT -p tcp --dport 443 -j ACCEPT # Block all other traffic iptables -A INPUT -j DROP For context, this machine is a Virtual Private Server Web app host. In a previous question, Lee B said that I should "lock down ICMP a bit more." Why not just block it altogether? What would happen if I did that (what bad thing would happen)? If I need to not block ICMP, how could I go about locking it down more?

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• Stop duplicate icmp echo replies when bridging to a dummy interface?

  - by mbrownnyc

  I recently configured a bridge br0 with members as eth0 (real if) and dummy0 (dummy.ko if). When I ping this machine, I receive duplicate replies as: # ping SERVERA PING SERVERA.domain.local (192.168.100.115) 56(84) bytes of data. 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=1 ttl=62 time=113 ms 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=1 ttl=62 time=114 ms (DUP!) 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=2 ttl=62 time=113 ms 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=2 ttl=62 time=113 ms (DUP!) Using tcpdump on SERVERA, I was able to see icmp echo replies being sent from eth0 and br0 itself as follows (oddly two echo request packets arrive "from" my Windows box myhost): 23:19:05.324192 IP myhost.domain.local > SERVERA.domain.local: ICMP echo request, id 512, seq 43781, length 40 23:19:05.324212 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324217 IP myhost.domain.local > SERVERA.domain.local: ICMP echo request, id 512, seq 43781, length 40 23:19:05.324221 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324264 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324272 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 It's worth noting, testing reveals that hosts on the same physical switch do not see DUP icmp echo responses (a host on the same VLAN on another switch does see a dup icmp echo response). I've read that this could be due to the ARP table of a switch, but I can't find any info directly related to bridges, just bonds. I have a feeling my problem lay in the stack on linux, not the switch, but am opened to any suggestions. The system is running centos6/el6 kernel 2.6.32-71.29.1.el6.i686. How do I stop ICMP echo replies from being sent in duplicate when dealing with a bridge interface/bridged interfaces? Thanks, Matt [edit] Quick note: It was recommended in #linux to: [08:53] == mbrownnyc [gateway/web/freenode/] has joined ##linux [08:57] <lkeijser> mbrownnyc: what happens if you set arp_ignore to 1 for the dummy interface? [08:59] <lkeijser> also set arp_announce to 2 for that interface [09:24] <mbrownnyc> lkeijser: I set arp_annouce to 2, arp_ignore to 2 in /etc/sysctl.conf and rebooted the machine... verifying that the bits are set after boot... the problem is still present I did this and came up empty. Same dup problem. I will be moving away from including the dummy interface in the bridge as: [09:31] == mbrownnyc [gateway/web/freenode/] has joined #Netfilter [09:31] <mbrownnyc> Hello all... I'm wondering, is it correct that even with an interface in PROMISC that the kernel will drop /some/ packets before they reach applications? [09:31] <whaffle> What would you make think so? [09:32] <mbrownnyc> I ask because I am receiving ICMP echo replies after configuring a bridge with a dummy interface in order for ipt_netflow to see all packets, only as reported in it's documentation: http://ipt-netflow.git.sourceforge.net/git/gitweb.cgi?p=ipt-netflow/ipt-netflow;a=blob;f=README.promisc [09:32] <mbrownnyc> but I do not know if PROMISC will do the same job [09:33] <mbrownnyc> I was referred here from #linux. any assistance is appreciated [09:33] <whaffle> The following conditions need to be met: PROMISC is enabled (bridges and applications like tcpdump will do this automatically, otherwise they won't function). [09:34] <whaffle> If an interface is part of a bridge, then all packets that enter the bridge should already be visible in the raw table. [09:35] <mbrownnyc> thanks whaffle PROMISC must be set manually for ipt_netflow to function, but [09:36] <whaffle> promisc does not need to be set manually, because the bridge will do it for you. [09:36] <whaffle> When you do not have a bridge, you can easily create one, thereby rendering any kernel patches moot. [09:36] <mbrownnyc> whaffle: I speak without the bridge [09:36] <whaffle> It is perfectly valid to have a "half-bridge" with only a single interface in it. [09:36] <mbrownnyc> whaffle: I am unfamiliar with the raw table, does this mean that PROMISC allows the raw table to be populated with packets the same as if the interface was part of a bridge? [09:37] <whaffle> Promisc mode will cause packets with {a dst MAC address that does not equal the interface's MAC address} to be delivered from the NIC into the kernel nevertheless. [09:37] <mbrownnyc> whaffle: I suppose I mean to clearly ask: what benefit would creating a bridge have over setting an interface PROMISC? [09:38] <mbrownnyc> whaffle: from your last answer I feel that the answer to my question is "none," is this correct? [09:39] <whaffle> Furthermore, the linux kernel itself has a check for {packets with a non-local MAC address}, so that packets that will not enter a bridge will be discarded as well, even in the face of PROMISC. [09:46] <mbrownnyc> whaffle: so, this last bit of information is quite clearly why I would need and want a bridge in my situation [09:46] <mbrownnyc> okay, the ICMP echo reply duplicate issue is likely out of the realm of this channel, but I sincerely appreciate the info on the kernels inner-workings [09:52] <whaffle> mbrownnyc: either the kernel patch, or a bridge with an interface. Since the latter is quicker, yes [09:54] <mbrownnyc> thanks whaffle [edit2] After removing the bridge, and removing the dummy kernel module, I only had a single interface chilling out, lonely. I still received duplicate icmp echo replies... in fact I received a random amount: http://pastebin.com/2LNs0GM8 The same thing doesn't happen on a few other hosts on the same switch, so it has to do with the linux box itself. I'll likely end up rebuilding it next week. Then... you know... this same thing will occur again. [edit3] Guess what? I rebuilt the box, and I'm still receiving duplicate ICMP echo replies. Must be the network infrastructure, although the ARP tables do not contain multiple entries. [edit4] How ridiculous. The machine was a network probe, so I was (ingress and egress) mirroring an uplink port to a node that was the NIC. So, the flow (must have) gone like this: ICMP echo request comes in through the mirrored uplink port. (the real) ICMP echo request is received by the NIC (the mirrored) ICMP echo request is received by the NIC ICMP echo reply is sent for both. I'm ashamed of myself, but now I know. It was suggested on #networking to either isolate the mirrored traffic to an interface that does not have IP enabled, or tag the mirrored packets with dot1q.

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• Some process does ICMP port scan on my OSX box and I am afraid my Mac got a virus

  - by Jamgold

  I noticed that my 10.6.6 box has some process send out ICMP messages to "random" hosts, which concerns me a lot. when doing a tcpdump icmp I see a lot of the following 15:41:14.738328 IP macpro > bzq-109-66-184-49.red.bezeqint.net: ICMP macpro udp port websm unreachable, length 36 15:41:15.110381 IP macpro > 99-110-211-191.lightspeed.sntcca.sbcglobal.net: ICMP macpro udp port 54045 unreachable, length 36 15:41:23.458831 IP macpro > 188.122.242.115: ICMP macpro udp port websm unreachable, length 36 15:41:23.638731 IP macpro > 61.85-200-21.bkkb.no: ICMP macpro udp port websm unreachable, length 36 15:41:27.329981 IP macpro > c-98-234-88-192.hsd1.ca.comcast.net: ICMP macpro udp port 54045 unreachable, length 36 15:41:29.349586 IP macpro > c-98-234-88-192.hsd1.ca.comcast.net: ICMP macpro udp port 54045 unreachable, length 36 I got suspicious when my router notified me about a lot of ICMP messages that don't get a response Does anyone know how to trace which process (or worse kernel module) might be responsible for this? I rebooted and logged in with a virgin user account and tcpdump showed the same results. Any dtrace magic welcome. Thanks in advance

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• ICMP Data Field Modified - What does it Mean?

  - by Lucretius

  Normal ICMP Data fields are composed of a pretty standard 32 byte string of alphabet characters. abcdefghijklmnopqrstuvwabcdefghi I have captured a series of ICMP echo requests using WireShark with a modified Data field and I have no idea what it means. (Underscores represent spaces.) abcdefghijklmnopprstuvwxyzabcdefghi abcdefghijklmnoparstuvwxyzabcdefghi __abcdefghijklmnopsrstuvwxyzabcdefghi __abcdefghijklmnopsrstuvwxyzabcdefghi __abcdefghijklmnopwrstuvwxyzabcdefghi __abcdefghijklmnopdrstuvwxyzabcdefghi__ Note: The position of the "q" character The addition of "xyz" The addition of spaces before and after the payload When you look at the position of "q" horizontally it spells "passwd" which is a Linux/Unix command for changing a users password. Any ideas?

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• Some process does ICMP port scan on my OSX box and I am afraid my Mac got a virus

  - by Jamgold

  I noticed that my 10.6.6 box has some process send out ICMP messages to "random" hosts, which concerns me a lot. when doing a tcpdump icmp I see a lot of the following 15:41:14.738328 IP macpro bzq-109-66-184-49.red.bezeqint.net: ICMP macpro udp port websm unreachable, length 36 15:41:15.110381 IP macpro 99-110-211-191.lightspeed.sntcca.sbcglobal.net: ICMP macpro udp port 54045 unreachable, length 36 15:41:23.458831 IP macpro 188.122.242.115: ICMP macpro udp port websm unreachable, length 36 15:41:23.638731 IP macpro 61.85-200-21.bkkb.no: ICMP macpro udp port websm unreachable, length 36 15:41:27.329981 IP macpro c-98-234-88-192.hsd1.ca.comcast.net: ICMP macpro udp port 54045 unreachable, length 36 15:41:29.349586 IP macpro c-98-234-88-192.hsd1.ca.comcast.net: ICMP macpro udp port 54045 unreachable, length 36 I got suspicious when my router notified me about a lot of ICMP messages that don't get a response Does anyone know how to trace which process (or worse kernel module) might be responsible for this? I rebooted and logged in with a virgin user account and tcpdump showed the same results. Any dtrace magic welcome. Thanks in advance

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• test of ICMP block

  - by Marcos

  In my bash scripts I have been using something like: until fping -u google.com; do echo "$0[$$] Network/DNS down?? $(date)" 1>&2 && sleep $(($RANDOM%(1 + ++trynum * 1) +1)).222; done to test for online connectivity. It halts in place, sleeping growing random intervals, until it can ping google.com again. Problem: At some sites ICMP pings are blocked altogether, and web pages are still reachable. What's a short way to test for this general case? Based on that test I will switch over to an http-based test like the exit status of curl -s google.com >/dev/null if that is a good one.

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• Is it possible to tunnel ICMP over TCP?

  - by Robert Atkins

  I don't want to tunnel TCP over ICMP (as ptunnel does), I want to go the other way around. I'm in the situation where I have TCP (HTTP) connectivity to a machine but an internal firewall over which I have no control is swallowing pings. The monitoring software I'm using appears to determine connectivity by attempting to send a ping before it tries to just connect to the web service on the target machine. It's failing this ping test and giving up. I believe if I could fool my monitoring software into thinking pings were getting through, it would then connect to the web service and be on its merry way. Anyone know how I can do this? I have SSH and root access on the destination machine.

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• Nagios dropping ICMP packets

  - by Ankh2054

  I am running a Nagios server on vmware 4.0 and every now and again during the day it alerts that some of servers cannot be reached via ICMP, clearly staging that a certain percentage of packets send are lost. This does not happen to all servers. I know the servers are actually up, because I have done a parallel test from another windows box, just using simple ping and no packets were lost. I also now from the way we monitor out switch that no packets were lost on those particular ports. Could anyone suggest a way to troubelshoot this further ? AT present this points to the nagios server itself loosing packets. thanks

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• Linux router: ping doesn't route back

  - by El Barto

  I have a Debian box which I'm trying to set up as a router and an Ubuntu box which I'm using as a client. My problem is that when the Ubuntu client tries to ping a server on the Internet, all the packets are lost (though, as you can see below, they seem to go to the server and back without problem). I'm doing this in the Ubuntu Box: # ping -I eth1 my.remote-server.com PING my.remote-server.com (X.X.X.X) from 10.1.1.12 eth1: 56(84) bytes of data. ^C --- my.remote-server.com ping statistics --- 13 packets transmitted, 0 received, 100% packet loss, time 12094ms (I changed the name and IP of the remote server for privacy). From the Debian Router I see this: # tcpdump -i eth1 -qtln icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 305, seq 7, length 64 IP 10.1.1.12 > X.X.X.X: ICMP echo request, id 305, seq 8, length 64 IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 305, seq 8, length 64 IP 10.1.1.12 > X.X.X.X: ICMP echo request, id 305, seq 9, length 64 IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 305, seq 9, length 64 IP 10.1.1.12 > X.X.X.X: ICMP echo request, id 305, seq 10, length 64 IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 305, seq 10, length 64 IP 10.1.1.12 > X.X.X.X: ICMP echo request, id 305, seq 11, length 64 IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 305, seq 11, length 64 ^C 9 packets captured 9 packets received by filter 0 packets dropped by kernel # tcpdump -i eth2 -qtln icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes IP 192.168.1.10 > X.X.X.X: ICMP echo request, id 360, seq 213, length 64 IP X.X.X.X > 192.168.1.10: ICMP echo reply, id 360, seq 213, length 64 IP 192.168.1.10 > X.X.X.X: ICMP echo request, id 360, seq 214, length 64 IP X.X.X.X > 192.168.1.10: ICMP echo reply, id 360, seq 214, length 64 IP 192.168.1.10 > X.X.X.X: ICMP echo request, id 360, seq 215, length 64 IP X.X.X.X > 192.168.1.10: ICMP echo reply, id 360, seq 215, length 64 IP 192.168.1.10 > X.X.X.X: ICMP echo request, id 360, seq 216, length 64 IP X.X.X.X > 192.168.1.10: ICMP echo reply, id 360, seq 216, length 64 IP 192.168.1.10 > X.X.X.X: ICMP echo request, id 360, seq 217, length 64 IP X.X.X.X > 192.168.1.10: ICMP echo reply, id 360, seq 217, length 64 ^C 10 packets captured 10 packets received by filter 0 packets dropped by kernel And at the remote server I see this: # tcpdump -i eth0 -qtln icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes IP Y.Y.Y.Y > X.X.X.X: ICMP echo request, id 360, seq 1, length 64 IP X.X.X.X > Y.Y.Y.Y: ICMP echo reply, id 360, seq 1, length 64 IP Y.Y.Y.Y > X.X.X.X: ICMP echo request, id 360, seq 2, length 64 IP X.X.X.X > Y.Y.Y.Y: ICMP echo reply, id 360, seq 2, length 64 IP Y.Y.Y.Y > X.X.X.X: ICMP echo request, id 360, seq 3, length 64 IP X.X.X.X > Y.Y.Y.Y: ICMP echo reply, id 360, seq 3, length 64 IP Y.Y.Y.Y > X.X.X.X: ICMP echo request, id 360, seq 4, length 64 IP X.X.X.X > Y.Y.Y.Y: ICMP echo reply, id 360, seq 4, length 64 IP Y.Y.Y.Y > X.X.X.X: ICMP echo request, id 360, seq 5, length 64 IP X.X.X.X > Y.Y.Y.Y: ICMP echo reply, id 360, seq 5, length 64 IP Y.Y.Y.Y > X.X.X.X: ICMP echo request, id 360, seq 6, length 64 IP X.X.X.X > Y.Y.Y.Y: ICMP echo reply, id 360, seq 6, length 64 IP Y.Y.Y.Y > X.X.X.X: ICMP echo request, id 360, seq 7, length 64 IP X.X.X.X > Y.Y.Y.Y: ICMP echo reply, id 360, seq 7, length 64 IP Y.Y.Y.Y > X.X.X.X: ICMP echo request, id 360, seq 8, length 64 IP X.X.X.X > Y.Y.Y.Y: ICMP echo reply, id 360, seq 8, length 64 IP Y.Y.Y.Y > X.X.X.X: ICMP echo request, id 360, seq 9, length 64 IP X.X.X.X > Y.Y.Y.Y: ICMP echo reply, id 360, seq 9, length 64 18 packets captured 228 packets received by filter 92 packets dropped by kernel Here "X.X.X.X" is my remote server's IP and "Y.Y.Y.Y" is my local network's public IP. So, what I understand is that the ping packets are coming out of the Ubuntu box (10.1.1.12), to the router (10.1.1.1), from there to the next router (192.168.1.1) and reaching the remote server (X.X.X.X). Then they come back all the way to the Debian router, but they never reach the Ubuntu box back. What am I missing? Here's the Debian router setup: # ifconfig eth1 Link encap:Ethernet HWaddr 94:0c:6d:82:0d:98 inet addr:10.1.1.1 Bcast:10.1.1.255 Mask:255.255.255.0 inet6 addr: fe80::960c:6dff:fe82:d98/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:105761 errors:0 dropped:0 overruns:0 frame:0 TX packets:48944 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:40298768 (38.4 MiB) TX bytes:44831595 (42.7 MiB) Interrupt:19 Base address:0x6000 eth2 Link encap:Ethernet HWaddr 6c:f0:49:a4:47:38 inet addr:192.168.1.10 Bcast:192.168.1.255 Mask:255.255.255.0 inet6 addr: fe80::6ef0:49ff:fea4:4738/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:38335992 errors:0 dropped:0 overruns:0 frame:0 TX packets:37097705 errors:0 dropped:0 overruns:0 carrier:1 collisions:0 txqueuelen:1000 RX bytes:4260680226 (3.9 GiB) TX bytes:3759806551 (3.5 GiB) Interrupt:27 eth3 Link encap:Ethernet HWaddr 94:0c:6d:82:c8:72 UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) Interrupt:20 Base address:0x2000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:3408 errors:0 dropped:0 overruns:0 frame:0 TX packets:3408 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:358445 (350.0 KiB) TX bytes:358445 (350.0 KiB) tun0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 inet addr:10.8.0.1 P-t-P:10.8.0.2 Mask:255.255.255.255 UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1 RX packets:2767779 errors:0 dropped:0 overruns:0 frame:0 TX packets:1569477 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:100 RX bytes:3609469393 (3.3 GiB) TX bytes:96113978 (91.6 MiB) # route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 10.8.0.2 0.0.0.0 255.255.255.255 UH 0 0 0 tun0 127.0.0.1 0.0.0.0 255.255.255.255 UH 0 0 0 lo 10.8.0.0 10.8.0.2 255.255.255.0 UG 0 0 0 tun0 192.168.1.0 0.0.0.0 255.255.255.0 U 1 0 0 eth2 10.1.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth2 # arp -n # Note: Here I have changed all the different MACs except the ones corresponding to the Ubuntu box (on 10.1.1.12 and 192.168.1.12) Address HWtype HWaddress Flags Mask Iface 192.168.1.118 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.72 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.94 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.102 ether NN:NN:NN:NN:NN:NN C eth2 10.1.1.12 ether 00:1e:67:15:2b:f0 C eth1 192.168.1.86 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.2 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.61 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.64 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.116 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.91 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.52 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.93 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.87 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.92 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.100 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.40 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.53 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.1 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.83 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.89 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.12 ether 00:1e:67:15:2b:f1 C eth2 192.168.1.77 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.66 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.90 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.65 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.41 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.78 ether NN:NN:NN:NN:NN:NN C eth2 192.168.1.123 ether NN:NN:NN:NN:NN:NN C eth2 # iptables -L -n Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination # iptables -L -n -t nat Chain PREROUTING (policy ACCEPT) target prot opt source destination Chain POSTROUTING (policy ACCEPT) target prot opt source destination MASQUERADE all -- 10.1.1.0/24 !10.1.1.0/24 MASQUERADE all -- !10.1.1.0/24 10.1.1.0/24 Chain OUTPUT (policy ACCEPT) target prot opt source destination And here's the Ubuntu box: # ifconfig eth0 Link encap:Ethernet HWaddr 00:1e:67:15:2b:f1 inet addr:192.168.1.12 Bcast:192.168.1.255 Mask:255.255.255.0 inet6 addr: fe80::21e:67ff:fe15:2bf1/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:28785139 errors:0 dropped:0 overruns:0 frame:0 TX packets:19050735 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:32068182803 (32.0 GB) TX bytes:6061333280 (6.0 GB) Interrupt:16 Memory:b1a00000-b1a20000 eth1 Link encap:Ethernet HWaddr 00:1e:67:15:2b:f0 inet addr:10.1.1.12 Bcast:10.1.1.255 Mask:255.255.255.0 inet6 addr: fe80::21e:67ff:fe15:2bf0/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:285086 errors:0 dropped:0 overruns:0 frame:0 TX packets:12719 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:30817249 (30.8 MB) TX bytes:2153228 (2.1 MB) Interrupt:16 Memory:b1900000-b1920000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:86048 errors:0 dropped:0 overruns:0 frame:0 TX packets:86048 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:11426538 (11.4 MB) TX bytes:11426538 (11.4 MB) # route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0 0.0.0.0 10.1.1.1 0.0.0.0 UG 100 0 0 eth1 10.1.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 10.8.0.0 192.168.1.10 255.255.255.0 UG 0 0 0 eth0 169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 eth0 192.168.1.0 0.0.0.0 255.255.255.0 U 1 0 0 eth0 # arp -n # Note: Here I have changed all the different MACs except the ones corresponding to the Debian box (on 10.1.1.1 and 192.168.1.10) Address HWtype HWaddress Flags Mask Iface 192.168.1.70 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.90 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.97 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.103 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.13 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.120 (incomplete) eth0 192.168.1.111 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.118 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.51 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.102 (incomplete) eth0 192.168.1.64 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.52 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.74 (incomplete) eth0 192.168.1.94 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.121 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.72 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.87 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.91 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.71 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.78 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.83 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.88 (incomplete) eth0 192.168.1.82 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.98 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.100 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.93 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.73 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.11 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.85 (incomplete) eth0 192.168.1.112 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.89 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.65 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.81 ether NN:NN:NN:NN:NN:NN C eth0 10.1.1.1 ether 94:0c:6d:82:0d:98 C eth1 192.168.1.53 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.116 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.61 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.10 ether 6c:f0:49:a4:47:38 C eth0 192.168.1.86 (incomplete) eth0 192.168.1.119 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.66 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.1 ether NN:NN:NN:NN:NN:NN C eth0 192.168.1.1 ether NN:NN:NN:NN:NN:NN C eth1 192.168.1.92 ether NN:NN:NN:NN:NN:NN C eth0 # iptables -L -n Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination # iptables -L -n -t nat Chain PREROUTING (policy ACCEPT) target prot opt source destination Chain INPUT (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination Chain POSTROUTING (policy ACCEPT) target prot opt source destination Edit: Following Patrick's suggestion, I did a tcpdump con the Ubuntu box and I see this: # tcpdump -i eth1 -qtln icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes IP 10.1.1.12 > X.X.X.X: ICMP echo request, id 21967, seq 1, length 64 IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 21967, seq 1, length 64 IP 10.1.1.12 > X.X.X.X: ICMP echo request, id 21967, seq 2, length 64 IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 21967, seq 2, length 64 IP 10.1.1.12 > X.X.X.X: ICMP echo request, id 21967, seq 3, length 64 IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 21967, seq 3, length 64 IP 10.1.1.12 > X.X.X.X: ICMP echo request, id 21967, seq 4, length 64 IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 21967, seq 4, length 64 IP 10.1.1.12 > X.X.X.X: ICMP echo request, id 21967, seq 5, length 64 IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 21967, seq 5, length 64 IP 10.1.1.12 > X.X.X.X: ICMP echo request, id 21967, seq 6, length 64 IP X.X.X.X > 10.1.1.12: ICMP echo reply, id 21967, seq 6, length 64 ^C 12 packets captured 12 packets received by filter 0 packets dropped by kernel So the question is: if all packets seem to be coming and going, why does ping report 100% packet loss?

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• ICMP - TTL - Trace Route

  - by dbasnett

  I asked this question at Stack Overflow and then thought this may be the better place to ask. Given the following situation: PC --- |aa RTR1 bb| --- |aa RTR2 bb| --- |aa RTR3 bb| etc Each of the |aa rtr bb| is meant to be a router with two ports aa and bb. My question is this. When you do a trace route from PC which router port address should respond with time to live exceeded in transit message? I seem to remember being taught to think of the router as being in as many parts as ports, so that in my scenario when aa is forwarding the packet to bb and decrements the ttl to 0, it will be the address of the aa port in the failure message. I am trying to find the definitive answer. Thanks.

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• Why do ICMP Redirct Host happen?

  - by El Barto

  I'm setting up a Debian box as a router for 4 subnets. For that I have defined 4 virtual interfaces on the NIC where the LAN is connected (eth1). eth1 Link encap:Ethernet HWaddr 94:0c:6d:82:0d:98 inet addr:10.1.1.1 Bcast:10.1.1.255 Mask:255.255.255.0 inet6 addr: fe80::960c:6dff:fe82:d98/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:6026521 errors:0 dropped:0 overruns:0 frame:0 TX packets:35331299 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:673201397 (642.0 MiB) TX bytes:177276932 (169.0 MiB) Interrupt:19 Base address:0x6000 eth1:0 Link encap:Ethernet HWaddr 94:0c:6d:82:0d:98 inet addr:10.1.2.1 Bcast:10.1.2.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Interrupt:19 Base address:0x6000 eth1:1 Link encap:Ethernet HWaddr 94:0c:6d:82:0d:98 inet addr:10.1.3.1 Bcast:10.1.3.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Interrupt:19 Base address:0x6000 eth1:2 Link encap:Ethernet HWaddr 94:0c:6d:82:0d:98 inet addr:10.1.4.1 Bcast:10.1.4.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Interrupt:19 Base address:0x6000 eth2 Link encap:Ethernet HWaddr 6c:f0:49:a4:47:38 inet addr:192.168.1.10 Bcast:192.168.1.255 Mask:255.255.255.0 inet6 addr: fe80::6ef0:49ff:fea4:4738/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:199809345 errors:0 dropped:0 overruns:0 frame:0 TX packets:158362936 errors:0 dropped:0 overruns:0 carrier:1 collisions:0 txqueuelen:1000 RX bytes:3656983762 (3.4 GiB) TX bytes:1715848473 (1.5 GiB) Interrupt:27 eth3 Link encap:Ethernet HWaddr 94:0c:6d:82:c8:72 inet addr:192.168.2.5 Bcast:192.168.2.255 Mask:255.255.255.0 inet6 addr: fe80::960c:6dff:fe82:c872/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:110814 errors:0 dropped:0 overruns:0 frame:0 TX packets:73386 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:16044901 (15.3 MiB) TX bytes:42125647 (40.1 MiB) Interrupt:20 Base address:0x2000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:22351 errors:0 dropped:0 overruns:0 frame:0 TX packets:22351 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:2625143 (2.5 MiB) TX bytes:2625143 (2.5 MiB) tun0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 inet addr:10.8.0.1 P-t-P:10.8.0.2 Mask:255.255.255.255 UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1 RX packets:41358924 errors:0 dropped:0 overruns:0 frame:0 TX packets:23116350 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:100 RX bytes:3065505744 (2.8 GiB) TX bytes:1324358330 (1.2 GiB) I have two other computers connected to this network. One has IP 10.1.1.12 (subnet mask 255.255.255.0) and the other one 10.1.2.20 (subnet mask 255.255.255.0). I want to be able to reach 10.1.1.12 from 10.1.2.20. Since packet forwarding is enabled in the router and the policy of the FORWARD chain is ACCEPT (and there are no other rules), I understand that there should be no problem to ping from 10.1.2.20 to 10.1.1.12 going through the router. However, this is what I get: $ ping -c15 10.1.1.12 PING 10.1.1.12 (10.1.1.12): 56 data bytes Request timeout for icmp_seq 0 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 81d4 0 0000 3f 01 e2b3 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 1 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 899b 0 0000 3f 01 daec 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 2 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 78fe 0 0000 3f 01 eb89 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 3 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 14b8 0 0000 3f 01 4fd0 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 4 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 8ef7 0 0000 3f 01 d590 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 5 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 ec9d 0 0000 3f 01 77ea 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 6 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 70e6 0 0000 3f 01 f3a1 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 7 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 b0d2 0 0000 3f 01 b3b5 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 8 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 f8b4 0 0000 3f 01 6bd3 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 9 Request timeout for icmp_seq 10 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 1c95 0 0000 3f 01 47f3 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 11 Request timeout for icmp_seq 12 Request timeout for icmp_seq 13 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 62bc 0 0000 3f 01 01cc 10.1.2.20 10.1.1.12 Why does this happen? From what I've read the Redirect Host response has something to do with the fact that the two hosts are in the same network and there being a shorter route (or so I understood). They are in fact in the same physical network, but why would there be a better route if they are not on the same subnet (they can't see each other)? What am I missing? Some extra info you might want to see: # route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 10.8.0.2 0.0.0.0 255.255.255.255 UH 0 0 0 tun0 127.0.0.1 0.0.0.0 255.255.255.255 UH 0 0 0 lo 192.168.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth3 10.8.0.0 10.8.0.2 255.255.255.0 UG 0 0 0 tun0 192.168.1.0 0.0.0.0 255.255.255.0 U 1 0 0 eth2 10.1.4.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 10.1.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 10.1.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 10.1.3.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth2 0.0.0.0 192.168.2.1 0.0.0.0 UG 100 0 0 eth3 # iptables -L -n Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination # iptables -L -n -t nat Chain PREROUTING (policy ACCEPT) target prot opt source destination Chain POSTROUTING (policy ACCEPT) target prot opt source destination MASQUERADE all -- !10.0.0.0/8 10.0.0.0/8 MASQUERADE all -- 10.0.0.0/8 !10.0.0.0/8 Chain OUTPUT (policy ACCEPT) target prot opt source destination

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• Why do ICMP Redirect Host happen?

  - by El Barto

  I'm setting up a Debian box as a router for 4 subnets. For that I have defined 4 virtual interfaces on the NIC where the LAN is connected (eth1). eth1 Link encap:Ethernet HWaddr 94:0c:6d:82:0d:98 inet addr:10.1.1.1 Bcast:10.1.1.255 Mask:255.255.255.0 inet6 addr: fe80::960c:6dff:fe82:d98/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:6026521 errors:0 dropped:0 overruns:0 frame:0 TX packets:35331299 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:673201397 (642.0 MiB) TX bytes:177276932 (169.0 MiB) Interrupt:19 Base address:0x6000 eth1:0 Link encap:Ethernet HWaddr 94:0c:6d:82:0d:98 inet addr:10.1.2.1 Bcast:10.1.2.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Interrupt:19 Base address:0x6000 eth1:1 Link encap:Ethernet HWaddr 94:0c:6d:82:0d:98 inet addr:10.1.3.1 Bcast:10.1.3.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Interrupt:19 Base address:0x6000 eth1:2 Link encap:Ethernet HWaddr 94:0c:6d:82:0d:98 inet addr:10.1.4.1 Bcast:10.1.4.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Interrupt:19 Base address:0x6000 eth2 Link encap:Ethernet HWaddr 6c:f0:49:a4:47:38 inet addr:192.168.1.10 Bcast:192.168.1.255 Mask:255.255.255.0 inet6 addr: fe80::6ef0:49ff:fea4:4738/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:199809345 errors:0 dropped:0 overruns:0 frame:0 TX packets:158362936 errors:0 dropped:0 overruns:0 carrier:1 collisions:0 txqueuelen:1000 RX bytes:3656983762 (3.4 GiB) TX bytes:1715848473 (1.5 GiB) Interrupt:27 eth3 Link encap:Ethernet HWaddr 94:0c:6d:82:c8:72 inet addr:192.168.2.5 Bcast:192.168.2.255 Mask:255.255.255.0 inet6 addr: fe80::960c:6dff:fe82:c872/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:110814 errors:0 dropped:0 overruns:0 frame:0 TX packets:73386 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:16044901 (15.3 MiB) TX bytes:42125647 (40.1 MiB) Interrupt:20 Base address:0x2000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:22351 errors:0 dropped:0 overruns:0 frame:0 TX packets:22351 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:2625143 (2.5 MiB) TX bytes:2625143 (2.5 MiB) tun0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 inet addr:10.8.0.1 P-t-P:10.8.0.2 Mask:255.255.255.255 UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1 RX packets:41358924 errors:0 dropped:0 overruns:0 frame:0 TX packets:23116350 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:100 RX bytes:3065505744 (2.8 GiB) TX bytes:1324358330 (1.2 GiB) I have two other computers connected to this network. One has IP 10.1.1.12 (subnet mask 255.255.255.0) and the other one 10.1.2.20 (subnet mask 255.255.255.0). I want to be able to reach 10.1.1.12 from 10.1.2.20. Since packet forwarding is enabled in the router and the policy of the FORWARD chain is ACCEPT (and there are no other rules), I understand that there should be no problem to ping from 10.1.2.20 to 10.1.1.12 going through the router. However, this is what I get: $ ping -c15 10.1.1.12 PING 10.1.1.12 (10.1.1.12): 56 data bytes Request timeout for icmp_seq 0 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 81d4 0 0000 3f 01 e2b3 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 1 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 899b 0 0000 3f 01 daec 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 2 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 78fe 0 0000 3f 01 eb89 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 3 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 14b8 0 0000 3f 01 4fd0 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 4 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 8ef7 0 0000 3f 01 d590 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 5 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 ec9d 0 0000 3f 01 77ea 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 6 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 70e6 0 0000 3f 01 f3a1 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 7 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 b0d2 0 0000 3f 01 b3b5 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 8 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 f8b4 0 0000 3f 01 6bd3 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 9 Request timeout for icmp_seq 10 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 1c95 0 0000 3f 01 47f3 10.1.2.20 10.1.1.12 Request timeout for icmp_seq 11 Request timeout for icmp_seq 12 Request timeout for icmp_seq 13 92 bytes from router2.mydomain.com (10.1.2.1): Redirect Host(New addr: 10.1.1.12) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 62bc 0 0000 3f 01 01cc 10.1.2.20 10.1.1.12 Why does this happen? From what I've read the Redirect Host response has something to do with the fact that the two hosts are in the same network and there being a shorter route (or so I understood). They are in fact in the same physical network, but why would there be a better route if they are not on the same subnet (they can't see each other)? What am I missing? Some extra info you might want to see: # route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 10.8.0.2 0.0.0.0 255.255.255.255 UH 0 0 0 tun0 127.0.0.1 0.0.0.0 255.255.255.255 UH 0 0 0 lo 192.168.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth3 10.8.0.0 10.8.0.2 255.255.255.0 UG 0 0 0 tun0 192.168.1.0 0.0.0.0 255.255.255.0 U 1 0 0 eth2 10.1.4.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 10.1.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 10.1.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 10.1.3.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth2 0.0.0.0 192.168.2.1 0.0.0.0 UG 100 0 0 eth3 # iptables -L -n Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination # iptables -L -n -t nat Chain PREROUTING (policy ACCEPT) target prot opt source destination Chain POSTROUTING (policy ACCEPT) target prot opt source destination MASQUERADE all -- !10.0.0.0/8 10.0.0.0/8 MASQUERADE all -- 10.0.0.0/8 !10.0.0.0/8 Chain OUTPUT (policy ACCEPT) target prot opt source destination

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• IP Tables won't save the rule.

  - by ArchUser

  Hello, I'm using ArchLinux and I have an IP tables rule that I know works (from my other server), and it's in /etc/iptables/iptables.rules, it's the only rule set in that directory. I run, /etc/rc.d/iptables save, then /etc/rc.d/iptables/restart, but when I do "iptables --list", I get ACCEPTs on INPUT,FORWARD & OUTPUT. # Generated by iptables-save v1.4.8 on Sat Jan 8 18:42:50 2011 *filter :INPUT DROP [0:0] :FORWARD DROP [0:0] :OUTPUT ACCEPT [216:14865] :BRUTEGUARD - [0:0] :interfaces - [0:0] :open - [0:0] -A INPUT -p icmp -m icmp --icmp-type 18 -j DROP -A INPUT -p icmp -m icmp --icmp-type 17 -j DROP -A INPUT -p icmp -m icmp --icmp-type 10 -j DROP -A INPUT -p icmp -m icmp --icmp-type 9 -j DROP -A INPUT -p icmp -m icmp --icmp-type 5 -j DROP -A INPUT -p icmp -j ACCEPT -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT -A INPUT -j interfaces -A INPUT -j open -A INPUT -p tcp -j REJECT --reject-with tcp-reset -A INPUT -p udp -j REJECT --reject-with icmp-port-unreachable -A INPUT -p tcp -m tcp ! --tcp-flags FIN,SYN,RST,ACK SYN -m state --state NEW -j DROP -A INPUT -f -j DROP -A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,SYN,RST,PSH,ACK,URG -j DROP -A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP -A INPUT -i eth+ -p icmp -m icmp --icmp-type 8 -j DROP -A BRUTEGUARD -m recent --set --name BF --rsource -A BRUTEGUARD -m recent --update --seconds 600 --hitcount 20 --name BF --rsource -j LOG --log-prefix "[BRUTEFORCE ATTEMPT] " --log-level 6 -A BRUTEGUARD -m recent --update --seconds 600 --hitcount 20 --name BF --rsource -j DROP -A interfaces -i lo -j ACCEPT -A open -p tcp -m tcp --dport 80 -j ACCEPT -A open -p tcp -m tcp --dport 10011 -j ACCEPT -A open -p udp -m udp --dport 9987 -j ACCEPT -A open -p tcp -m tcp --dport 30033 -j ACCEPT -A open -p tcp -m tcp --dport 8000 -j ACCEPT -A open -p tcp -m tcp --dport 8001 -j ACCEPT -A open -s 76.119.125.61 -p tcp -m tcp --dport 21 -j ACCEPT -A open -s 76.119.125.61 -p tcp -m tcp --dport 3306 -j ACCEPT -A open -p tcp -m tcp --dport 22 -j BRUTEGUARD -A open -s 76.119.125.61 -p tcp -m tcp --dport 22 -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT COMMIT # Completed on Sat Jan 8 18:42:50 2011

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• Blocking ICMP outgoing requests only in eth1

  - by Raj

  I am creating a NAT with iptables: Computer A: eth0 (dhcp) + eth1 (static ip 192.168.0.1 - gateway) Computer B: eth1 (static ip 192.168.0.2, using Computer A as gateway) I know how to block ICMP outgoing requests (-A OUTPUT -p icmp --icmp-type echo-request -j DROP), but that would block ICMP requests from Computer A, but not from Computer B (in fact, only for Computer A - Computer B can keep doing those). I tried with the same command, but adding -o eth1, but that does not block at all. Any idea?

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• Why do some web servers not respond to icmp requests?

  - by John Himmelman

  What is the purpose of blocking/dropping inbound ICMP traffic on a public web server? Is it common for it be blocked? I had to test if a server was accessible from various locations (tested on various servers located in different states/countries). I'd rely on ping as a quick & reliable method of determining if a server was online/network-accessible. After not receiving a response on a couple boxes, I tried using lynx to load the site, and it worked.

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• Linux - Only first virtual interface can ping external gateway

  - by husvar

  I created 3 virtual interfaces with different mac addresses all linked to the same physical interface. I see that they successfully arp for the gw and they can ping (the request is coming in the packet capture in wireshark). However the ping utility does not count the responses. Does anyone knows the issue? I am running Ubuntu 14.04 in a VmWare. root@ubuntu:~# ip link sh 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000 link/ether 00:0c:29:bc:fc:8b brd ff:ff:ff:ff:ff:ff root@ubuntu:~# ip addr sh 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 link/ether 00:0c:29:bc:fc:8b brd ff:ff:ff:ff:ff:ff inet6 fe80::20c:29ff:febc:fc8b/64 scope link valid_lft forever preferred_lft forever root@ubuntu:~# ip route sh root@ubuntu:~# ip link add link eth0 eth0.1 addr 00:00:00:00:00:11 type macvlan root@ubuntu:~# ip link add link eth0 eth0.2 addr 00:00:00:00:00:22 type macvlan root@ubuntu:~# ip link add link eth0 eth0.3 addr 00:00:00:00:00:33 type macvlan root@ubuntu:~# ip -4 link sh 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000 link/ether 00:0c:29:bc:fc:8b brd ff:ff:ff:ff:ff:ff 18: eth0.1@eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default link/ether 00:00:00:00:00:11 brd ff:ff:ff:ff:ff:ff 19: eth0.2@eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default link/ether 00:00:00:00:00:22 brd ff:ff:ff:ff:ff:ff 20: eth0.3@eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default link/ether 00:00:00:00:00:33 brd ff:ff:ff:ff:ff:ff root@ubuntu:~# ip -4 addr sh 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever root@ubuntu:~# ip -4 route sh root@ubuntu:~# dhclient -v eth0.1 Internet Systems Consortium DHCP Client 4.2.4 Copyright 2004-2012 Internet Systems Consortium. All rights reserved. For info, please visit https://www.isc.org/software/dhcp/ Listening on LPF/eth0.1/00:00:00:00:00:11 Sending on LPF/eth0.1/00:00:00:00:00:11 Sending on Socket/fallback DHCPDISCOVER on eth0.1 to 255.255.255.255 port 67 interval 3 (xid=0x568eac05) DHCPREQUEST of 192.168.1.145 on eth0.1 to 255.255.255.255 port 67 (xid=0x568eac05) DHCPOFFER of 192.168.1.145 from 192.168.1.254 DHCPACK of 192.168.1.145 from 192.168.1.254 bound to 192.168.1.145 -- renewal in 1473 seconds. root@ubuntu:~# dhclient -v eth0.2 Internet Systems Consortium DHCP Client 4.2.4 Copyright 2004-2012 Internet Systems Consortium. All rights reserved. For info, please visit https://www.isc.org/software/dhcp/ Listening on LPF/eth0.2/00:00:00:00:00:22 Sending on LPF/eth0.2/00:00:00:00:00:22 Sending on Socket/fallback DHCPDISCOVER on eth0.2 to 255.255.255.255 port 67 interval 3 (xid=0x21e3114e) DHCPREQUEST of 192.168.1.146 on eth0.2 to 255.255.255.255 port 67 (xid=0x21e3114e) DHCPOFFER of 192.168.1.146 from 192.168.1.254 DHCPACK of 192.168.1.146 from 192.168.1.254 bound to 192.168.1.146 -- renewal in 1366 seconds. root@ubuntu:~# dhclient -v eth0.3 Internet Systems Consortium DHCP Client 4.2.4 Copyright 2004-2012 Internet Systems Consortium. All rights reserved. For info, please visit https://www.isc.org/software/dhcp/ Listening on LPF/eth0.3/00:00:00:00:00:33 Sending on LPF/eth0.3/00:00:00:00:00:33 Sending on Socket/fallback DHCPDISCOVER on eth0.3 to 255.255.255.255 port 67 interval 3 (xid=0x11dc5f03) DHCPREQUEST of 192.168.1.147 on eth0.3 to 255.255.255.255 port 67 (xid=0x11dc5f03) DHCPOFFER of 192.168.1.147 from 192.168.1.254 DHCPACK of 192.168.1.147 from 192.168.1.254 bound to 192.168.1.147 -- renewal in 1657 seconds. root@ubuntu:~# ip -4 link sh 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000 link/ether 00:0c:29:bc:fc:8b brd ff:ff:ff:ff:ff:ff 18: eth0.1@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default link/ether 00:00:00:00:00:11 brd ff:ff:ff:ff:ff:ff 19: eth0.2@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default link/ether 00:00:00:00:00:22 brd ff:ff:ff:ff:ff:ff 20: eth0.3@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default link/ether 00:00:00:00:00:33 brd ff:ff:ff:ff:ff:ff root@ubuntu:~# ip -4 addr sh 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever 18: eth0.1@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default inet 192.168.1.145/24 brd 192.168.1.255 scope global eth0.1 valid_lft forever preferred_lft forever 19: eth0.2@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default inet 192.168.1.146/24 brd 192.168.1.255 scope global eth0.2 valid_lft forever preferred_lft forever 20: eth0.3@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default inet 192.168.1.147/24 brd 192.168.1.255 scope global eth0.3 valid_lft forever preferred_lft forever root@ubuntu:~# ip -4 route sh default via 192.168.1.254 dev eth0.1 192.168.1.0/24 dev eth0.1 proto kernel scope link src 192.168.1.145 192.168.1.0/24 dev eth0.2 proto kernel scope link src 192.168.1.146 192.168.1.0/24 dev eth0.3 proto kernel scope link src 192.168.1.147 root@ubuntu:~# arping -c 5 -I eth0.1 192.168.1.254 ARPING 192.168.1.254 from 192.168.1.145 eth0.1 Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 6.936ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 2.986ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 0.654ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 5.137ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 2.426ms Sent 5 probes (1 broadcast(s)) Received 5 response(s) root@ubuntu:~# arping -c 5 -I eth0.2 192.168.1.254 ARPING 192.168.1.254 from 192.168.1.146 eth0.2 Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 5.665ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 3.753ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 16.500ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 3.287ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 32.438ms Sent 5 probes (1 broadcast(s)) Received 5 response(s) root@ubuntu:~# arping -c 5 -I eth0.3 192.168.1.254 ARPING 192.168.1.254 from 192.168.1.147 eth0.3 Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 4.422ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 2.429ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 2.321ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 40.423ms Unicast reply from 192.168.1.254 [58:98:35:57:a0:70] 2.268ms Sent 5 probes (1 broadcast(s)) Received 5 response(s) root@ubuntu:~# tcpdump -n -i eth0.1 -v & [1] 5317 root@ubuntu:~# ping -c5 -q -I eth0.1 192.168.1.254 PING 192.168.1.254 (192.168.1.254) from 192.168.1.145 eth0.1: 56(84) bytes of data. tcpdump: listening on eth0.1, link-type EN10MB (Ethernet), capture size 65535 bytes 13:18:37.612558 IP (tos 0x0, ttl 64, id 2595, offset 0, flags [DF], proto ICMP (1), length 84) 192.168.1.145 > 192.168.1.254: ICMP echo request, id 5318, seq 2, length 64 13:18:37.618864 IP (tos 0x68, ttl 64, id 14493, offset 0, flags [none], proto ICMP (1), length 84) 192.168.1.254 > 192.168.1.145: ICMP echo reply, id 5318, seq 2, length 64 13:18:37.743650 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.1.87 tell 192.168.1.86, length 46 13:18:38.134997 IP (tos 0x0, ttl 128, id 23547, offset 0, flags [none], proto UDP (17), length 229) 192.168.1.86.138 > 192.168.1.255.138: NBT UDP PACKET(138) 13:18:38.614580 IP (tos 0x0, ttl 64, id 2596, offset 0, flags [DF], proto ICMP (1), length 84) 192.168.1.145 > 192.168.1.254: ICMP echo request, id 5318, seq 3, length 64 13:18:38.793479 IP (tos 0x68, ttl 64, id 14495, offset 0, flags [none], proto ICMP (1), length 84) 192.168.1.254 > 192.168.1.145: ICMP echo reply, id 5318, seq 3, length 64 13:18:39.151282 IP6 (class 0x68, hlim 255, next-header ICMPv6 (58) payload length: 32) fe80::5a98:35ff:fe57:e070 > ff02::1:ff6b:e9b4: [icmp6 sum ok] ICMP6, neighbor solicitation, length 32, who has 2001:818:d812:da00:8ae3:abff:fe6b:e9b4 source link-address option (1), length 8 (1): 58:98:35:57:a0:70 13:18:39.615612 IP (tos 0x0, ttl 64, id 2597, offset 0, flags [DF], proto ICMP (1), length 84) 192.168.1.145 > 192.168.1.254: ICMP echo request, id 5318, seq 4, length 64 13:18:39.746981 IP (tos 0x68, ttl 64, id 14496, offset 0, flags [none], proto ICMP (1), length 84) 192.168.1.254 > 192.168.1.145: ICMP echo reply, id 5318, seq 4, length 64 --- 192.168.1.254 ping statistics --- 5 packets transmitted, 5 received, 0% packet loss, time 4008ms rtt min/avg/max/mdev = 2.793/67.810/178.934/73.108 ms root@ubuntu:~# killall tcpdump >> /dev/null 2>&1 9 packets captured 12 packets received by filter 0 packets dropped by kernel [1]+ Done tcpdump -n -i eth0.1 -v root@ubuntu:~# tcpdump -n -i eth0.2 -v & [1] 5320 root@ubuntu:~# ping -c5 -q -I eth0.2 192.168.1.254 PING 192.168.1.254 (192.168.1.254) from 192.168.1.146 eth0.2: 56(84) bytes of data. tcpdump: listening on eth0.2, link-type EN10MB (Ethernet), capture size 65535 bytes 13:18:41.536874 ARP, Ethernet (len 6), IPv4 (len 4), Reply 192.168.1.254 is-at 58:98:35:57:a0:70, length 46 13:18:41.536933 IP (tos 0x0, ttl 64, id 2599, offset 0, flags [DF], proto ICMP (1), length 84) 192.168.1.146 > 192.168.1.254: ICMP echo request, id 5321, seq 1, length 64 13:18:41.539255 IP (tos 0x68, ttl 64, id 14507, offset 0, flags [none], proto ICMP (1), length 84) 192.168.1.254 > 192.168.1.146: ICMP echo reply, id 5321, seq 1, length 64 13:18:42.127715 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.1.87 tell 192.168.1.86, length 46 13:18:42.511725 IP (tos 0x0, ttl 64, id 2600, offset 0, flags [DF], proto ICMP (1), length 84) 192.168.1.146 > 192.168.1.254: ICMP echo request, id 5321, seq 2, length 64 13:18:42.514385 IP (tos 0x68, ttl 64, id 14527, offset 0, flags [none], proto ICMP (1), length 84) 192.168.1.254 > 192.168.1.146: ICMP echo reply, id 5321, seq 2, length 64 13:18:42.743856 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.1.87 tell 192.168.1.86, length 46 13:18:43.511727 IP (tos 0x0, ttl 64, id 2601, offset 0, flags [DF], proto ICMP (1), length 84) 192.168.1.146 > 192.168.1.254: ICMP echo request, id 5321, seq 3, length 64 13:18:43.513768 IP (tos 0x68, ttl 64, id 14528, offset 0, flags [none], proto ICMP (1), length 84) 192.168.1.254 > 192.168.1.146: ICMP echo reply, id 5321, seq 3, length 64 13:18:43.637598 IP (tos 0x0, ttl 128, id 23551, offset 0, flags [none], proto UDP (17), length 225) 192.168.1.86.17500 > 255.255.255.255.17500: UDP, length 197 13:18:43.641185 IP (tos 0x0, ttl 128, id 23552, offset 0, flags [none], proto UDP (17), length 225) 192.168.1.86.17500 > 192.168.1.255.17500: UDP, length 197 13:18:43.641201 IP (tos 0x0, ttl 128, id 23553, offset 0, flags [none], proto UDP (17), length 225) 192.168.1.86.17500 > 255.255.255.255.17500: UDP, length 197 13:18:43.743890 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.1.87 tell 192.168.1.86, length 46 13:18:44.510758 IP (tos 0x0, ttl 64, id 2602, offset 0, flags [DF], proto ICMP (1), length 84) 192.168.1.146 > 192.168.1.254: ICMP echo request, id 5321, seq 4, length 64 13:18:44.512892 IP (tos 0x68, ttl 64, id 14538, offset 0, flags [none], proto ICMP (1), length 84) 192.168.1.254 > 192.168.1.146: ICMP echo reply, id 5321, seq 4, length 64 13:18:45.510794 IP (tos 0x0, ttl 64, id 2603, offset 0, flags [DF], proto ICMP (1), length 84) 192.168.1.146 > 192.168.1.254: ICMP echo request, id 5321, seq 5, length 64 13:18:45.519701 IP (tos 0x68, ttl 64, id 14539, offset 0, flags [none], proto ICMP (1), length 84) 192.168.1.254 > 192.168.1.146: ICMP echo reply, id 5321, seq 5, length 64 13:18:49.287554 IP6 (class 0x68, hlim 255, next-header ICMPv6 (58) payload length: 32) fe80::5a98:35ff:fe57:e070 > ff02::1:ff6b:e9b4: [icmp6 sum ok] ICMP6, neighbor solicitation, length 32, who has 2001:818:d812:da00:8ae3:abff:fe6b:e9b4 source link-address option (1), length 8 (1): 58:98:35:57:a0:70 13:18:50.013463 IP (tos 0x0, ttl 255, id 50737, offset 0, flags [DF], proto UDP (17), length 73) 192.168.1.146.5353 > 224.0.0.251.5353: 0 [2q] PTR (QM)? _ipps._tcp.local. PTR (QM)? _ipp._tcp.local. (45) 13:18:50.218874 IP6 (class 0x68, hlim 255, next-header ICMPv6 (58) payload length: 32) fe80::5a98:35ff:fe57:e070 > ff02::1:ff6b:e9b4: [icmp6 sum ok] ICMP6, neighbor solicitation, length 32, who has 2001:818:d812:da00:8ae3:abff:fe6b:e9b4 source link-address option (1), length 8 (1): 58:98:35:57:a0:70 13:18:51.129961 IP6 (class 0x68, hlim 255, next-header ICMPv6 (58) payload length: 32) fe80::5a98:35ff:fe57:e070 > ff02::1:ff6b:e9b4: [icmp6 sum ok] ICMP6, neighbor solicitation, length 32, who has 2001:818:d812:da00:8ae3:abff:fe6b:e9b4 source link-address option (1), length 8 (1): 58:98:35:57:a0:70 13:18:52.197074 IP6 (hlim 255, next-header UDP (17) payload length: 53) 2001:818:d812:da00:200:ff:fe00:22.5353 > ff02::fb.5353: [udp sum ok] 0 [2q] PTR (QM)? _ipps._tcp.local. PTR (QM)? _ipp._tcp.local. (45) 13:18:54.128240 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.1.87 tell 192.168.1.86, length 46 --- 192.168.1.254 ping statistics --- 5 packets transmitted, 0 received, 100% packet loss, time 4000ms root@ubuntu:~# killall tcpdump >> /dev/null 2>&1 13:18:54.657731 IP6 (class 0x68, hlim 255, next-header ICMPv6 (58) payload length: 32) fe80::5a98:35ff:fe57:e070 > ff02::1:ff6b:e9b4: [icmp6 sum ok] ICMP6, neighbor solicitation, length 32, who has 2001:818:d812:da00:8ae3:abff:fe6b:e9b4 source link-address option (1), length 8 (1): 58:98:35:57:a0:70 13:18:54.743174 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.1.87 tell 192.168.1.86, length 46 25 packets captured 26 packets received by filter 0 packets dropped by kernel [1]+ Done tcpdump -n -i eth0.2 -v root@ubuntu:~# tcpdump -n -i eth0.3 icmp & [1] 5324 root@ubuntu:~# ping -c5 -q -I eth0.3 192.168.1.254 PING 192.168.1.254 (192.168.1.254) from 192.168.1.147 eth0.3: 56(84) bytes of data. tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0.3, link-type EN10MB (Ethernet), capture size 65535 bytes 13:18:56.373434 IP 192.168.1.147 > 192.168.1.254: ICMP echo request, id 5325, seq 1, length 64 13:18:57.372116 IP 192.168.1.147 > 192.168.1.254: ICMP echo request, id 5325, seq 2, length 64 13:18:57.381263 IP 192.168.1.254 > 192.168.1.147: ICMP echo reply, id 5325, seq 2, length 64 13:18:58.371141 IP 192.168.1.147 > 192.168.1.254: ICMP echo request, id 5325, seq 3, length 64 13:18:58.373275 IP 192.168.1.254 > 192.168.1.147: ICMP echo reply, id 5325, seq 3, length 64 13:18:59.371165 IP 192.168.1.147 > 192.168.1.254: ICMP echo request, id 5325, seq 4, length 64 13:18:59.373259 IP 192.168.1.254 > 192.168.1.147: ICMP echo reply, id 5325, seq 4, length 64 13:19:00.371211 IP 192.168.1.147 > 192.168.1.254: ICMP echo request, id 5325, seq 5, length 64 13:19:00.373278 IP 192.168.1.254 > 192.168.1.147: ICMP echo reply, id 5325, seq 5, length 64 --- 192.168.1.254 ping statistics --- 5 packets transmitted, 1 received, 80% packet loss, time 4001ms rtt min/avg/max/mdev = 13.666/13.666/13.666/0.000 ms root@ubuntu:~# killall tcpdump >> /dev/null 2>&1 9 packets captured 10 packets received by filter 0 packets dropped by kernel [1]+ Done tcpdump -n -i eth0.3 icmp root@ubuntu:~# arp -n Address HWtype HWaddress Flags Mask Iface 192.168.1.254 ether 58:98:35:57:a0:70 C eth0.1 192.168.1.254 ether 58:98:35:57:a0:70 C eth0.2 192.168.1.254 ether 58:98:35:57:a0:70 C eth0.3

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• Some process does ICMP port scan on my OSX box and I am afraid my Mac got a virus

  - by Jamgold

  I noticed that my 10.6.6 box has some process send out ICMP messages to "random" hosts, which concerns me a lot. when doing a tcpdump icmp I see a lot of the following 15:41:14.738328 IP macpro > bzq-109-66-184-49.red.bezeqint.net: ICMP macpro udp port websm unreachable, length 36 15:41:15.110381 IP macpro > 99-110-211-191.lightspeed.sntcca.sbcglobal.net: ICMP macpro udp port 54045 unreachable, length 36 15:41:23.458831 IP macpro > 188.122.242.115: ICMP macpro udp port websm unreachable, length 36 15:41:23.638731 IP macpro > 61.85-200-21.bkkb.no: ICMP macpro udp port websm unreachable, length 36 15:41:27.329981 IP macpro > c-98-234-88-192.hsd1.ca.comcast.net: ICMP macpro udp port 54045 unreachable, length 36 15:41:29.349586 IP macpro > c-98-234-88-192.hsd1.ca.comcast.net: ICMP macpro udp port 54045 unreachable, length 36 I got suspicious when my router notified me about a lot of ICMP messages that don't get a response [INFO] Mon Jan 10 16:31:47 2011 Blocked outgoing ICMP packet (ICMP type 3) from 192.168.1.189 to 212.25.57.90 Does anyone know how to trace which process (or worse kernel module) might be responsible for this? I rebooted and logged in with a virgin user account and tcpdump showed the same results. Any dtrace magic welcome. Thanks in advance

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• how do I get the IP of incoming ICMP due to UDP-send to dead client in Ruby?

  - by banister

  so.. I'm doing a small multiplayer game with blocking UDP and IO.select. To my problem.. (In the server) reading from a UDP socket (packet, sender = @socket.recvfrom(1000)) which have just sent a packet to a dead client results in a ICMP unreachable (and exception Errno::ECONNRESET in ruby). The problem is that I can't find any way whatsoever to extract the IP of that ICMP.. so I can clean out that dead client. Anyone know how to achieve this? thanks

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