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• CentOS - massive usage on loopback interface

  - by Matthew Iselin

  Hi, I have a CentOS installation which is running fairly smoothly. Today I ran ifconfig mainly to see what sort of usage has been coming across the ethernet interface, and to also check my link speed. This is what I ended up seeing for the loopback device: lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:10301085132061223274 errors:0 dropped:0 overruns:0 frame:0 TX packets:13981054163812689233 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:11783901785008000095 (0.6 EiB) TX bytes:10333501021200548281 (0.9 EiB) This just feels completely wrong - almost an EiB of data? Any assistance in tracking down the source of these statistics would be greatly appreciated.

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• multicast tcpdump and subscriptions

  - by Karoly Horvath

  From the multicast howto: IP_ADD_MEMBERSHIP. Recall that you need to tell the kernel which multicast groups you are interested in. If no process is interested in a group, packets destined to it that arrive to the host are discarded. If you don't do that, you won't see those packets with tcpdump. Is it possible to subscribe to all multicast traffic so I can do a tcpdump for all existing traffic? I would think IGMP doesn't allow this, so probably not.. but maybe you can configure a switch to still send all multicast traffic. Is that possible? Is it possible to do subscription (for a specific IP) with a command line tool? (note: I know how to do this in C.. but would prefer to use an existing tool and not compile a separate program for this)

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• Ping isn't acting accurate?

  - by Earlz

  I've been trying to diagnose some latency issues with my internet connection. I've been lagging out of online video games and such, which of course could be their server's fault. So, I've been running ping some. It doesn't indicate anything unusual, but it does act a bit strange. I can start it with something like ping internethost -i 0.1 so that it will send a ton of packets, and every 10-20 seconds it will appear to just freeze for 2 or 3 seconds. The packets are still being received in the right order though, and there is no packet loss. The weirdest thing is that after the little freeze up, it will usually just report a ping time that is about 10-30ms higher than the average. How does this happen? Is ping still being accurate? I'm using Arch Linux. The host I'm pinging is my website, which shouldn't be doing any kind of ping slowing or filtering.

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• Confusion about TCP packet analysis terms

  - by Berkay

  I'm analyzing our network and have some confusion about the terms: this is the 2-packet output from source to destination. from these i have to get some features as describe, pls make me clear... packets with at least a bytes of TCP data payload: it seems tcp.len0; The minimum segment size (confusion is headers are included or or not) The average segment size observed during the lifetime of the connection, the definition: is calculated as the value reported in the actual data bytes divided by the actual data pkts reported. Total bytes in IP packets, should be ip_len value. Total bytes in (Ethernet) The total number of bytes sent probably related to frame.len and frame.cap_len these two terms are describes as, also make me clear about these two terms. frame.cap_len: Frame length stored into the capture file frame.len: Frame length on the wire

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• Unable to connect to mysql through JDBC connector through Tomcat or externally.

  - by iftrue

  I've installed a stock mysql 5.5 installation, and while I can connect to the mysql service via the mysql command, and the service seems to be running, I cannot connect to it through spring+tomcat or from an external jdbc connector. I'm using the following URL: jdbc:mysql://myserver.com:myport/mydb with proper username/password, but I receive the following message: server.com: Communications link failure The last packet sent successfully to the server was 0 milliseconds ago. the driver has not received any packets from the server. and tomcat throws: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) Which seems to be the same issue as if I try to connect externally.

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• Using Linode as a proxy server wrapped in DNS to bypass paid internet services

  - by snihalani

  I have a linode server that I use for development. I was thinking of using that as a proxy server. I have noticed that most paid connections allow DNS queries but don't allow http until I pay them. I verified this by flushing my dns cache and nslookup some random websites. How do I create a proxy server that allows me to may be wrap my packets from my computer in DNS packets, relay to my linode server with ssh key authentication and act as a broker? Thanks.

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• On an unencrypted public wi-fi hotspot, what exactly is a packet sniffer doing to get another computer's packet?

  - by hal10001

  I get mixed results when reading information security articles, some of them stating that in order to do something similar you need to also setup some sort of honeypot with a running access point and local Web server to intercept traffic. Then other articles seem to indicate you don't need that, and you can just run Wireshark, and it will detect all packets being sent on the network. How could that be, and what exactly is a packet sniffer doing to get those packets? Does this involve intercepting wireless signals transmitted over the wireless protocol and frequency via the NIC on the computer running a program like Wireshark?

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• Multicast accross the subnets

  - by Hasan Khan

  My application sends some UDP packets on a multicast address. In our office we have 3 subnets connected via routers. Sitting in my subnet I'm able to ping the IP of the other subnet. Will multicast packets cross my subnet and reach the machines of other subnets? Or router will need some configuration? Or do I have to program a bridge for it? Please note that I do not know anything about Networking. Kindly tell me something that I can ask my network admin to do.

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• Can't send emails through sendmail, error occured

  - by skomak

  Hi, I have sendmail MTA and i use pear:Mail class to send mails through remote sendmail server. Everything was fine till yesterday. Probably nothing changes was made in configs. At maillog i can see: May 6 12:58:55 xxx sendmail[25903]: STARTTLS=server, relay=hostxxxx.static.xx.xx.pl [85.x.x.x], version=TLSv1/SSLv3, verify=NO, cipher=DHE-RSA-AES256-SHA, bits=256/256 May 6 12:58:56 xxx sendmail[25903]: o46AwtqE025903: hostxxxx.static.xx.xx.pl [85.x.x.x] did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA2 and in /var/log/messages: May 6 13:00:17 lilia sendmail[27193]: realm changed: authentication aborted I use ldap to authenticate users but i used the same script to check mailing on another server and it works there good, only this server behave weird. Packets are deliverd to sendmail server i can see it in tcpdump, but there is smaller packets than on other server which sends emails. Could you tell me how can i check what is wrong with that? D.S.

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• Local Area Connection in Slacware 13

  - by asdasd

  I have windows xp and slackware 13 on one computer, and the ISP provided me a new modem. There was manual how to configure it, so i start the web browser and typed it's ip address 192.168.1.1 and the web interface of the modem appeared so i logged in, that was easy. But under slackware, i don't know how to enter in the modem config / web interface. I type in 192.168.1.1 but it's not working. Here's the output of ifconfig eth0 : eth0 Link encap:Ethernet HWaddr 00:a1:b0:01:18:28 inet addr:169.254.73.8 Bcast:169.254.255.255 Mask:255.255.0.0 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:17 Memory:febff400-febff4ff How can i log in into the modem from linux, i.e. find it's assigned ip under slackware ? Thank you.

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• External routing for local interfaces in a virtualized network

  - by Arkaitz Jimenez

  Current setup: br0| |-- tun10 -pipe-tun0(192.240.240.1) |-- tun11 -pipe-tun1(192.240.240.2) |-- tun12 -pipe-tun2(192.240.240.3) The pipe program is a custom program that forwards data back2back between two tun interfaces. The idea is puting 2 programs in .2 and .3 while keeping .1 as the local interface in the current machine. The main problem is that I want to route packets to .2 and to .3 through .1 and br0, but as they are local interfaces, the kernel ignores any routing instruction, it just delivers the packet to the proper interface. Tried iptables, but the nat table doesn't even see ping packets to those ifaces. A "ping 192.240.240.2" delivers a icmp packet with source and dest .2 to tun1, ideally it should deliver a source .1 dest .2 at tun1 through tun0-br0-tun1 Any hint? Here the output of some commands: Output

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• iptables blocking ssh communication

  - by Michal Sapsa

  I'm using this script for iptables: #!/bin/sh echo "1" > /proc/sys/net/ipv4/ip_forward iptables -F iptables -X iptables -F -t nat iptables -X -t nat iptables -F -t filter iptables -X -t filter iptables -t filter -P FORWARD DROP iptables -t filter -A FORWARD -s 192.168.0.0/255.255.0.0 -d 0/0 -j ACCEPT iptables -t filter -A FORWARD -s 0/0 -d 192.168.0.0/255.255.0.0 -j ACCEPT iptables -t nat -A POSTROUTING -s 10.8.0.1/255.255.255.0 -j MASQUERADE iptables -A FORWARD -s 10.8.0.1/255.255.255.0 -j ACCEPT iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -d 0/0 -j MASQUERADE iptables -I FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu iptables -t nat -A PREROUTING -i eth1 -p udp --dport 16161 -j DNAT --to 192.168.0.251:16161 iptables -t nat -A PREROUTING -i eth1 -p udp --sport 16161 -j DNAT --to 192.168.0.251:16161 #openvpn iptables -I INPUT -p tcp --dport 1194 -j ACCEPT iptables -I INPUT -p udp --dport 1194 -j ACCEPT I end up with some iptables rules that should work but don't work - probably because of me. # Generated by iptables-save v1.4.12 on Mon May 26 13:15:43 2014 *raw :PREROUTING ACCEPT [1657523:1357257330] :OUTPUT ACCEPT [36804:34834370] -A PREROUTING -p icmp -j TRACE -A PREROUTING -p tcp -j TRACE -A OUTPUT -p icmp -j TRACE -A OUTPUT -p tcp -j TRACE COMMIT # Completed on Mon May 26 13:15:43 2014 # Generated by iptables-save v1.4.12 on Mon May 26 13:15:43 2014 *nat :PREROUTING ACCEPT [5033:345623] :INPUT ACCEPT [154:34662] :OUTPUT ACCEPT [6:1968] :POSTROUTING ACCEPT [2:120] -A PREROUTING -i eth0 -p tcp -m tcp --dport 16161 -j DNAT --to-destination 192.168.0.251:22 -A PREROUTING -i eth1 -p tcp -m tcp --dport 16161 -j DNAT --to-destination 192.168.0.251:22 -A POSTROUTING -s 10.8.0.0/24 -j MASQUERADE -A POSTROUTING -s 192.168.0.0/24 -j MASQUERADE COMMIT # Completed on Mon May 26 13:15:44 2014 # Generated by iptables-save v1.4.12 on Mon May 26 13:15:44 2014 *filter :INPUT ACCEPT [548:69692] :FORWARD DROP [8:384] :OUTPUT ACCEPT [2120:1097479] -A INPUT -p udp -m udp --dport 1194 -j ACCEPT -A INPUT -p tcp -m tcp --dport 1194 -j ACCEPT -A FORWARD -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu -A FORWARD -s 192.168.0.0/16 -j ACCEPT -A FORWARD -d 192.168.0.0/16 -j ACCEPT -A FORWARD -s 10.8.0.0/24 -j ACCEPT -A FORWARD -i eth0 -o eth1 -p tcp -m tcp --dport 22 -j ACCEPT -A FORWARD -i eth1 -o eth0 -p tcp -m tcp --dport 22 -j ACCEPT COMMIT TRACE at PREROUTEING AND OUTPUT are only for debuging this thing. When I ssh at public ip with port 16161 I don't get any message, only TimeOut so it looks like I don't get communication back to remote server. ETH0 is the world, ETH1 is LAN Any IPTABLES Masters willing to give a hand ? iptables -vL Chain INPUT (policy ACCEPT 20548 packets, 3198K bytes) pkts bytes target prot opt in out source destination 38822 7014K ACCEPT udp -- any any anywhere anywhere udp dpt:openvpn 0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:openvpn Chain FORWARD (policy DROP 1129 packets, 64390 bytes) pkts bytes target prot opt in out source destination 214K 11M TCPMSS tcp -- any any anywhere anywhere tcpflags: SYN,RST/SYN TCPMSS clamp to PMTU 4565K 1090M ACCEPT all -- any any 192.168.0.0/16 anywhere 5916K 7315M ACCEPT all -- any any anywhere 192.168.0.0/16 0 0 ACCEPT all -- any any 10.8.0.0/24 anywhere 0 0 ACCEPT tcp -- any any anywhere 192.168.0.251 tcp dpt:16161 Chain OUTPUT (policy ACCEPT 59462 packets, 19M bytes) pkts bytes target prot opt in out source destination

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• Allow VMWare client to connect only via VPN

  - by Frank Meulenaar

  I have a VMWare (currently using Workstation on Vista, but thinking about switching to ESX) client with Windows XP. I've installed OpenVPN in the client and it connects to the corporate VPN server. I want to make sure that all traffic from the Windows XP machine goes trough this VPN tunnel, but I can't change any settings on the corporate VPN server. Is it possible to restrict the internet connectivity of the Windows XP client in such a way that it can only send packets to the IP of the corporate VPN server? In that way it'd be impossible for packets to bypass the tunnel. I've looked at NAT configurations but couldn't see how I could make this setup.

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• The ping response time doesn't reflect the real network response time

  - by yangchenyun

  I encountered a weird problem that the response time returned by ping is almost fixed at 98ms. Either I ping the gateway, or I ping a local host or a internet host. The response time is always around 98ms although the actual delay is obvious. However, the reverse ping (from a local machine to this host) works properly. The following is my route table and the result: 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 100 0 0 eth1 60.194.136.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 eth1 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 # ping the gateway ping 192.168.1.1 PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data. 64 bytes from 192.168.1.1: icmp_req=1 ttl=64 time=98.7 ms 64 bytes from 192.168.1.1: icmp_req=2 ttl=64 time=97.0 ms 64 bytes from 192.168.1.1: icmp_req=3 ttl=64 time=96.0 ms 64 bytes from 192.168.1.1: icmp_req=4 ttl=64 time=94.9 ms 64 bytes from 192.168.1.1: icmp_req=5 ttl=64 time=94.0 ms ^C --- 192.168.1.1 ping statistics --- 5 packets transmitted, 5 received, 0% packet loss, time 4004ms rtt min/avg/max/mdev = 94.030/96.149/98.744/1.673 ms #ping a local machine ping 192.168.1.88 PING 192.168.1.88 (192.168.1.88) 56(84) bytes of data. 64 bytes from 192.168.1.88: icmp_req=1 ttl=64 time=98.7 ms 64 bytes from 192.168.1.88: icmp_req=2 ttl=64 time=96.9 ms 64 bytes from 192.168.1.88: icmp_req=3 ttl=64 time=96.0 ms 64 bytes from 192.168.1.88: icmp_req=4 ttl=64 time=95.0 ms ^C --- 192.168.1.88 ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3003ms rtt min/avg/max/mdev = 95.003/96.696/98.786/1.428 ms #ping a internet host ping google.com PING google.com (74.125.128.139) 56(84) bytes of data. 64 bytes from hg-in-f139.1e100.net (74.125.128.139): icmp_req=1 ttl=42 time=99.8 ms 64 bytes from hg-in-f139.1e100.net (74.125.128.139): icmp_req=2 ttl=42 time=99.9 ms 64 bytes from hg-in-f139.1e100.net (74.125.128.139): icmp_req=3 ttl=42 time=99.9 ms 64 bytes from hg-in-f139.1e100.net (74.125.128.139): icmp_req=4 ttl=42 time=99.9 ms ^C64 bytes from hg-in-f139.1e100.net (74.125.128.139): icmp_req=5 ttl=42 time=99.9 ms --- google.com ping statistics --- 5 packets transmitted, 5 received, 0% packet loss, time 32799ms rtt min/avg/max/mdev = 99.862/99.925/99.944/0.284 ms I am running iperf to test the bandwidth, the rate is quite low for a LAN connection. iperf -c 192.168.1.87 -t 50 -i 10 -f M ------------------------------------------------------------ Client connecting to 192.168.1.87, TCP port 5001 TCP window size: 0.06 MByte (default) ------------------------------------------------------------ [ 4] local 192.168.1.139 port 54697 connected with 192.168.1.87 port 5001 [ ID] Interval Transfer Bandwidth [ 4] 0.0-10.0 sec 6.12 MBytes 0.61 MBytes/sec [ 4] 10.0-20.0 sec 6.38 MBytes 0.64 MBytes/sec [ 4] 20.0-30.0 sec 6.38 MBytes 0.64 MBytes/sec [ 4] 30.0-40.0 sec 6.25 MBytes 0.62 MBytes/sec [ 4] 40.0-50.0 sec 6.38 MBytes 0.64 MBytes/sec [ 4] 0.0-50.1 sec 31.6 MBytes 0.63 MBytes/sec

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• CentOS: eth0 not starting on boot

  - by Cameron Aziz

  Whenever I reboot a CentOS Hyper-V VM, eth0 does not start automatically. All I need to do is perform ifup eth0 and all is fixed, but that isn't feasible from ssh! I am starting in runlevel 3. After I perform ifup eth0 on the console: [root@localhost ~]# ifconfig eth0 Link encap:Ethernet HWaddr 00:15:5D:2B:2B:07 inet addr:10.10.0.3 Bcast:10.10.0.255 Mask:255.255.255.0 inet6 addr: fe80::215:5dff:fe2b:2b07/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:34 errors:0 dropped:0 overruns:0 frame:0 TX packets:49 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:4656 (4.5 KiB) TX bytes:6399 (6.2 KiB) Interrupt:9 Base address:0xa000 [root@localhost ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0 DEVICE=eth0 BOOTPROTO=none IPADDR=10.10.0.3 NETMASK=255.255.255.0 GATEWAY=10.10.0.1 USERCTL=no ONBOOT=yes [root@localhost ~]# chkconfig --list | grep network network 0:off 1:off 2:on 3:on 4:on 5:on 6:off

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• The best software for users internet usage

  - by nikospkrk

  Hi, We are a small business using a Vigor 2820 as the internet router, and we'd like to install a software that could report any internet usage from our users. I already tried the "official" software made by Draytek called "SmartMonitor", but is reliability is a real issue as it doesn't seem to keep capturing packets after working 3 to 6hours (randomly), whereas Wireshark keeps capturing packets after that amount of time. As I'm really fed up with this tool, I'm looking for other solutions but I still want the same features: users statistics, websites ranking, users traffic, ... I already enabled the port mirroring feature, so it would be perfect if you could suggest me a port mirroring-based software (ideally freeware). I thought I had found the good one with Etherscout, but it just doesn't launch. I am even open to a tool that would "just" make some reports based on Wireshark captured files (*.pcap). Thank you for any of your suggestion, Nicolas.

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• Resolve Wrong IP from Domain Name only on certain networks

  - by Godric Seer

  I host a personal website on an old desktop that is LAMP based. There are several strange things about this problem so I will break it down into steps. Since I have a dynamic IP, I use no-ip to make sure I have a working domain name at all times. I use the automatic update client, but logged in and checked and my no-ip domain has the proper IP tied to it. Here is a link to the homepage through the no-ip domain for reference. Also, I do a ping and a traceroute on the no-ip domain and get: [eckertzs@localhost ~]$ ping -c 1 endradil.noip.me PING endradil.noip.me (65.24.215.99) 56(84) bytes of data. 64 bytes from endradil.noip.me (65.24.215.99): icmp_seq=1 ttl=64 time=2.23 ms --- endradil.noip.me ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 104ms rtt min/avg/max/mdev = 2.233/2.233/2.233/0.000 ms [eckertzs@localhost ~]$ traceroute endradil.noip.me traceroute to endradil.noip.me (65.24.215.99), 30 hops max, 60 byte packets 1 . (192.168.2.1) 1.755 ms 5.409 ms 5.380 ms 2 endradil.noip.me (65.24.215.99) 6.297 ms 9.543 ms 10.324 ms Using this domain, I can connect to my webserver without issue or interruption(the https is required to avoid a redirect serverside, but it works). I also have a domain I have bought on GoDaddy where I have a CNAME record forwarding the www subdomain to my no-ip domain. CNAME Record Host: www Points to: endradil.noip.me TTL: 1 hour For the past several weeks, I never had an issue using the GoDaddy domain to connect (ssh or https). As of the past few days, however, the GoDaddy domain has only worked intermittently, for a few minutes at a time and then will go down for hours at a time. I get server not found errors most of the time. Also, if I happen to be using the GoDaddy domain for an ssh connection, the connection will freeze. I have run online tests of the DNS and have seen that the website is visible by external servers and resolved to the correct IP. I also contacted GoDaddy support but they had no issues connecting to the website, and therefore did not see any issues. My personal computers (Windows desktop, linux laptop, android phone) all fail to connect when on my personal wifi. If I disconnect my phone from the wifi and use my AT&T wireless data, it can connect with both domains without issue. When I attempt to use Google webmaster tools to crawl the site using the GoDaddy domain, Google can not find the site. From my linux laptop, I have found some interesting results when I ping or traceroute the domain. The results from these: [eckertzs@localhost ~]$ ping -c 1 www.endradil.com PING www.endradil.com.Belkin (198.105.244.228) 56(84) bytes of data. --- www.endradil.com.Belkin ping statistics --- 1 packets transmitted, 0 received, 100% packet loss, time 10000ms [eckertzs@localhost ~]$ traceroute www.endradil.com traceroute to www.endradil.com (198.105.244.228), 30 hops max, 60 byte packets 1 . (192.168.2.1) 1.918 ms 2.806 ms 2.772 ms 2 cpe-65-24-208-1.insight.res.rr.com (65.24.208.1) 29.247 ms 29.654 ms 30.094 ms 3 cpe-69-23-24-117.new.res.rr.com (69.23.24.117) 15.597 ms 23.218 ms 23.581 ms 4 agg24.clmcohib01r.midwest.rr.com (65.29.1.52) 30.581 ms 30.556 ms 31.192 ms 5 be27.clevohek01r.midwest.rr.com (65.29.1.38) 30.580 ms 31.062 ms 31.038 ms 6 bu-ether25.atlngamq47w-bcr01.tbone.rr.com (107.14.19.38) 37.863 ms 68.844 ms 43.773 ms 7 107.14.17.178 (107.14.17.178) 51.866 ms 51.019 ms 50.989 ms 8 ae0.pr1.dca10.tbone.rr.com (107.14.17.200) 48.467 ms ae-4-0.a0.lax91.tbone.rr.com (66.109.1.113) 49.912 ms * 9 v413.core1.ash1.he.net (209.51.175.33) 60.270 ms 50.842 ms 50.819 ms 10 100ge5-1.core1.nyc4.he.net (184.105.223.166) 55.597 ms 56.045 ms 56.020 ms 11 xerocole-inc.10gigabitethernet12-4.core1.nyc4.he.net (216.66.41.242) 56.001 ms 55.969 ms 55.992 ms 12 * * * both show the incorrect IP. Also, the traceroute timesout on hops 12 through 255 (output truncated above). The traceroute using site24x7 works and shows reasonable results when run from their california server. From another linux box on a different network but in the same city as me (10 miles away), I still get timeout for traceroute, however the IP resolves correctly for the domain. From this I believe that the DNS result is incorrectly cached in either my router/modem or perhaps even at my ISP level. My question is, first, how do I find out exactly what is wrong, and second, how do I resolve it.

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• How can I log all traffic with its exact length?

  - by Legate

  I want to process all packets with their size going through our gateway server (running Debian 4.0). My idea is to use tcpdump, but I have two questions. The command I'm currently thinking of is tcpdump -i iface -n -t -q. Is it guaranteed that tcpdump will process all packets? What happens if the CPU is working to full capacity? The format of the output lines is IP ddd.ddd.ddd.ddd.port > ddd.ddd.ddd.ddd.port: tcp 1260. What exactly is 1260? I have the suspicion that it is the payload in bytes of the packet, which would be exactly what I need, but I'm not sure. It might be the TCP Window Size. Or perhaps there is an even better way of doing this? I thought about a LOG rule in iptables, but tcpdump seems easier and I don't know whether iptables can log the packet lengths.

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• Correct way of bringing network interface down in linux

  - by Karolis T.

  For example: $ ifconfig dummy0 up $ ifconfig dummy0 "192.168.1.190 netmask 255.255.255.0" Calling ifconfig with no parameters shows the interface dummy0 Link encap:Ethernet HWaddr b6:1f:f3:92:6d:20 inet addr:192.168.1.190 Bcast:192.168.1.255 Mask:255.255.255.0 inet6 addr: fe80::b41f:f3ff:fe92:6d20/64 Scope:Link UP BROADCAST RUNNING NOARP MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:15 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 B) TX bytes:1050 (1.0 KiB) How can I bring the interface down so that it doesn't show up in ifconfig ifconfig -a ifconfig dummy0 without rmmod dummy because dummy is used just for example purposes. If there is no way to do that, what "throw-away" IP could I set to it and be safe from any trouble? like $ ifconfig dummy0 down $ ifconfig dummy0 0.0.0.0

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• Unable to PPTP through NAT on Cisco 881

  - by MasterRoot24

  I'm trying to connect to a PPTP server which is sat behind a Cisco 881 NAT router. The server is running Ubuntu Server 12.04 and is running Poptop pptpd as the PPTP daemon listening for connections. As discussed in my other question, I'm trying to setup a Cisco 881 router to replace my old Linksys WAG320N. This same server and WAN connection worked fine with the WAG320N with no special configuration, other than allowing 1723 in through the firewall. On the Cisco 881, I'm using the newer ip nat enable or NAT NVI to setup static routes in through the firewall for the services running behind the router. My reason being that I can't run another copy of my live DNS domains internally with local IP addresses in. For the purposes of this question, though, I have rebuilt the router with ip nat inside/outside style NAT'ing, but this issue is still apparent. HTTP/SMTP/IMAP etc. all work ok from both the WAN and LAN interfaces of the router. I'm only having issues with SIP (see other question) and PPTP. My issue is that the GRE doesn't appear to be passing through NAT correctly and one end of the connection is not receiving GRE traffic when it should be, so the server hangs up the connection. Here's an example of /var/log/syslog with debug enabled in /etc/pptpd.conf: Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: MGR: Launching /usr/sbin/pptpctrl to handle client Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: local address = 192.168.1.50 Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: remote address = 192.168.1.51 Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: pppd options file = /etc/ppp/pptpd-options Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: Client 82.132.248.216 control connection started Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: Received PPTP Control Message (type: 1) Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: Made a START CTRL CONN RPLY packet Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: I wrote 156 bytes to the client. Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: Sent packet to client Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: Received PPTP Control Message (type: 7) Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: Set parameters to 100000000 maxbps, 64 window size Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: Made a OUT CALL RPLY packet Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: Starting call (launching pppd, opening GRE) Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: pty_fd = 6 Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: tty_fd = 7 Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: I wrote 32 bytes to the client. Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: CTRL: Sent packet to client Dec 11 21:06:30 <HOSTNAME> pptpd[22627]: CTRL (PPPD Launcher): program binary = /usr/sbin/pppd Dec 11 21:06:30 <HOSTNAME> pptpd[22627]: CTRL (PPPD Launcher): local address = 192.168.1.50 Dec 11 21:06:30 <HOSTNAME> pptpd[22627]: CTRL (PPPD Launcher): remote address = 192.168.1.51 Dec 11 21:06:30 <HOSTNAME> pppd[22627]: Plugin /usr/lib/pptpd/pptpd-logwtmp.so loaded. Dec 11 21:06:30 <HOSTNAME> pppd[22627]: pppd 2.4.5 started by root, uid 0 Dec 11 21:06:30 <HOSTNAME> pppd[22627]: Using interface ppp0 Dec 11 21:06:30 <HOSTNAME> pppd[22627]: Connect: ppp0 <--> /dev/pts/3 Dec 11 21:06:30 <HOSTNAME> pptpd[22626]: GRE: Bad checksum from pppd. Dec 11 21:06:31 <HOSTNAME> pptpd[22626]: CTRL: Received PPTP Control Message (type: 15) Dec 11 21:06:31 <HOSTNAME> pptpd[22626]: CTRL: Got a SET LINK INFO packet with standard ACCMs Dec 11 21:07:00 <HOSTNAME> pppd[22627]: LCP: timeout sending Config-Requests Dec 11 21:07:00 <HOSTNAME> pppd[22627]: Connection terminated. Dec 11 21:07:00 <HOSTNAME> avahi-daemon[1042]: Withdrawing workstation service for ppp0. Dec 11 21:07:00 <HOSTNAME> pppd[22627]: Modem hangup Dec 11 21:07:00 <HOSTNAME> pppd[22627]: Exit. Dec 11 21:07:00 <HOSTNAME> pptpd[22626]: GRE: read(fd=6,buffer=6075a0,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs Dec 11 21:07:00 <HOSTNAME> pptpd[22626]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7) Dec 11 21:07:00 <HOSTNAME> pptpd[22626]: CTRL: Reaping child PPP[22627] Dec 11 21:07:00 <HOSTNAME> pptpd[22626]: CTRL: Client 82.132.248.216 control connection finished Dec 11 21:07:00 <HOSTNAME> pptpd[22626]: CTRL: Exiting now Dec 11 21:07:00 <HOSTNAME> pptpd[5803]: MGR: Reaped child 22626 As far as Cisco are concerned, all I need is ip nat source static tcp <SERVER LAN IP> 1723 interface FastEthernet4 1723 but of course this doesn't seem to the be helping the GRE traffic through as it should. Trying the connection to the LAN IP of the server from the same LAN as the server (behind the router), the PPTP connection works fine, so I'm confident that the server's config is ok. Furthermore, all I needed on my WAG320N was to open 1723 in the firewall. Here's my current router config: ! ! Last configuration change at 20:20:15 UTC Tue Dec 11 2012 by xxx version 15.2 no service pad service timestamps debug datetime msec service timestamps log datetime msec service password-encryption ! hostname xxx ! boot-start-marker boot-end-marker ! ! enable secret 4 xxxx ! aaa new-model ! ! aaa authentication login local_auth local ! ! ! ! ! aaa session-id common ! memory-size iomem 10 ! crypto pki trustpoint TP-self-signed-xxx enrollment selfsigned subject-name cn=IOS-Self-Signed-Certificate-xxx revocation-check none rsakeypair TP-self-signed-xxx ! ! crypto pki certificate chain TP-self-signed-xxx certificate self-signed 01 xxx quit ip gratuitous-arps ip auth-proxy max-login-attempts 5 ip admission max-login-attempts 5 ! ! ! ! ! ip domain list dmz.xxx.local ip domain list xxx.local ip domain name dmz.xxx.local ip name-server 192.168.1.x ip cef login block-for 3 attempts 3 within 3 no ipv6 cef ! ! multilink bundle-name authenticated license udi pid CISCO881-SEC-K9 sn xxx ! ! username admin privilege 15 secret 4 xxx username joe secret 4 xxx ! ! ! ! ! ip ssh time-out 60 ! ! ! ! ! ! ! ! ! interface FastEthernet0 no ip address ! interface FastEthernet1 no ip address ! interface FastEthernet2 no ip address ! interface FastEthernet3 switchport access vlan 2 no ip address ! interface FastEthernet4 ip address dhcp ip nat enable duplex auto speed auto ! interface Vlan1 ip address 192.168.1.x 255.255.255.0 no ip redirects no ip unreachables no ip proxy-arp ip nat enable ! interface Vlan2 ip address 192.168.0.x 255.255.255.0 ! ip forward-protocol nd ip http server ip http access-class 1 ip http authentication local ip http secure-server ! ! ip nat source list 1 interface FastEthernet4 overload ip nat source list 2 interface FastEthernet4 overload ip nat source static tcp 192.168.1.x 1723 interface FastEthernet4 1723 ! ! access-list 1 permit 192.168.0.0 0.0.0.255 access-list 2 permit 192.168.1.0 0.0.0.255 ! ! ! ! control-plane ! ! banner motd Authorized Access only ! line con 0 exec-timeout 15 0 login authentication local_auth line aux 0 exec-timeout 15 0 login authentication local_auth line vty 0 4 access-class 2 in login authentication local_auth length 0 transport input all ! ! end UPDATE 16/12/2012: The only progress that I have been able to make on this issue is that I'm confident that the issue is caused by the GRE tunnels (which are required for the PPTP connection to complete) are being blocked. When attempting a connection, I can see in show ip nat nvi translations that both a TCP translation on 1723 is setup and also a GRE translation is setup also. I appear to be able to see GRE related packets on the LAN that the server is on, so I am lead to believe that the server is sending(?) GRE packets, however running Wireshark on a client PC when attempting a connection shows absolutely no GRE packets. Whilst there are no configuration directives in my config posted above (that I can pin point) which would specifically block them, it would appear that the GRE packets are not being allowed in/out of the router's firewall, even though a NAT translation entry is setup to the server's LAN address. Would anyone be able to provide me with some help to ensure that GRE packets are not blocked by the router's firewall, so that this can be ruled out as a possible issue please?

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• Unable to connect to mysql through JDBC connector through Tomcat or externally

  - by Stefan Kendall

  I've installed a stock mysql 5.5 installation, and while I can connect to the mysql service via the mysql command, and the service seems to be running, I cannot connect to it through spring+tomcat or from an external jdbc connector. I'm using the following URL: jdbc:mysql://myserver.com:myport/mydb with proper username/password, but I receive the following message: server.com: Communications link failure The last packet sent successfully to the server was 0 milliseconds ago. the driver has not received any packets from the server. and tomcat throws: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) Which seems to be the same issue as if I try to connect externally.

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• AWS EC2: How to determine whether my EC2/scalr AMI was hacked? What to do to secure it?

  - by Niro

  I received notification from Amazon that my instance tried to hack another server. there was no additional information besides log dump: Original report: Destination IPs: Destination Ports: Destination URLs: Abuse Time: Sun May 16 10:13:00 UTC 2010 NTP: N Log Extract: External 184.xxx.yyy.zzz, 11.842.000 packets/300s (39.473 packets/s), 5 flows/300s (0 flows/s), 0,320 GByte/300s (8 MBit/s) (184.xxx.yyy.zzz is my instance ip) How can I tell whether someone has penetrated my instance? What are the steps I should take to make sure my instance is clean and safe to use? Is there some intrusion detection techinque or log that I can use? Any information is highly appreciated.

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• How to block own rpcap traffic where tshark is running?

  - by Pankaj Goyal

  Platform :- Fedora 13 32-bit machine RemoteMachine$ ./rpcapd -n ClientMachine$ tshark -w "filename" -i "any interface name" As soon as capture starts without any capture filter, thousands of packets get captured. Rpcapd binds to 2002 port by default and while establishing the connection it sends a randomly chosen port number to the client for further communication. Both client and server machines exchange tcp packets through randomly chosen ports. So, I cannot even specify the capture filter to block this rpcap related tcp traffic. Wireshark & tshark for Windows have an option "Do not capture own Rpcap Traffic" in Remote Settings in Edit Interface Dialog box. But there is no such option in tshark for linux. It will be also better if anyone can tell me how wireshark blocks rpcap traffic....

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• hung up troubleshooting packet discards

  - by Chris Satola

  I realize my question is generic, but hopefully someone may have some guidance for me. My network consists of Cisco switches. I am seeing a significant amount (upwards of millions of packets per day) transmit drops between two switches. One being a 3750 and the other a 3560. The peak throughput of this link is only upper 400Mbps, so it shouldn't be a bandwidth issue. At this point, I am sort of clueless where to look or what tools I can use to determine what packets are dropping and why. I can setup a SPAN port on that link and wireshark it, but I don't know if that could tell me anything. Does anyone have any suggestions? Thanks in advance.

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• A Linux DHCP server that will listen on an non-broadcast (tap) interface?

  - by TomOnTime

  Are there any Linux DHCP servers that will listen to what Cisco calls an "unnumbered" interface, or what others might call a "NBMA" (non-broadcast) interface. I have a Linux system that connects to a number of others using GRE tunnels. The machines on the other end send DHCP requests to this machine, I can see them with tcpdump. However, ISC DHCP 3.0.3 refuses to listen to the interface because it is non-broadcast. The interface I'd like DHCP to listen to is: tap2 Link encap:Ethernet HWaddr removed-for-privacy inet6 addr: removed-for-privacy/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:518 errors:0 dropped:0 overruns:0 frame:0 TX packets:510 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:500 RX bytes:196242 (191.6 KiB) TX bytes:52425 (51.1 KiB)

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