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• network latency, TCP and UDP packets

  - by user115848

  Hello recently my network has started to cause me lots of problems. I have a cable modem, connected to a tp-link router (with some port forwarding). Everything was working fine then i started to get lots of udp (port 53) "UNREPLIED" logs in the router. Now there are tcp UNREPLIED logs too. This is causing lots of latency and failed connections when trying to connect to different internet sites. Also, we run an openfire server for spark connections, and I believe its causing connectivity issues for some users who are trying to connect using Spark (some people connect fine, others don't). Please see screen shot below for packet logs. It has to be something internally, as I connected straight to the comcast modem and i was able to connect to the internet and various sites as normal. I tried to swap out the router with a different and got the same issue. I scanned both my internal dns servers for viruses or malware and it came up empty. Another anomaly is that when i try to connect to www.cnn.com, i get redirected to the different site. I scanned my own machine for hijacks. Not sure if this is related to the networking issue. Please let me know if you have any ideas for troubleshooting.

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• How to fix massive lag on ZyXEL HomePlug AV powerline adapters?

  - by Tim Abell

  I have 3 ZyXEL Homeplug AV powerline adapters as per the one in the review below. I have two plugged in currently, one into my Be / Thompson wireless router, and one into my desktop pc (box1). every now and then the link indicator on the adapters (the mains link, not the ethernet link) goes nutty, and performance falls off a cliff (see below). http://www.gadgetspeak.com/gadget/article.rhtm/753/479266/ZyXEL_PowerLine_HomePlug_AV_PLA401.html 64 bytes from box1 (192.168.1.101): icmp_seq=1064 ttl=64 time=996 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1065 ttl=64 time=549 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1066 ttl=64 time=6.15 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1067 ttl=64 time=1400 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1068 ttl=64 time=812 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1069 ttl=64 time=11.1 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1070 ttl=64 time=1185 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1071 ttl=64 time=501 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1072 ttl=64 time=1975 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1073 ttl=64 time=970 ms ^C --- box1 ping statistics --- 1074 packets transmitted, 394 received, +487 errors, 63% packet loss, time 1082497ms rtt min/avg/max/mdev = 5.945/598.452/3526.454/639.768 ms, pipe 4 Any idea how to diagnose/fix? I'm on linux so installing the windoze software that came with them is not something I'm terribly keen to do.

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• Load balancing a Windows File Share using HA-Proxy

  - by NathanE

  After pulling my hair out over DFS I just had this weird and potentially dangerous idea come into my head whereby, just possibly, I might be able to use HA-Proxy to load balance a file share between servers. I've done some remedial packet traces and it does appear that TCP port 445 is the only thing involved in using Windows file sharing. I've always thought for many years that UDP 139, 135 etc were also involved in at least establishing the connection - but apparently not! So I setup a basic test: listen SMBTest *:445 mode tcp server Smb1 172.16.61.201:445 server Smb2 172.16.61.202:445 And you'll never guess what... it works??? (!) Now obviously there is the whole concern about synchronisation between the file servers (of course). That could easily be taken care of with a little bit of Robocopy script. And considering I only need a HA read-only file share there wouldn't be any issues with regard to file locking etc. Can anyone tell me if what I'm playing with here is fire? I really didn't think it would work at all and now I'm a little shocked. What would be the downsides? Could this be relied upon for a production environment?

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• Why can't I route to some sites from my MacBook Pro that I can see from my iPad? [closed]

  - by Robert Atkins

  I am on M1 Cable (residential) broadband in Singapore. I have an intermittent problem routing to some sites from my MacBook Pro—often Google-related sites (arduino.googlecode.com and ajax.googleapis.com right now, but sometimes even gmail.com.) This prevents StackExchange chat from working, for instance. Funny thing is, my iPad can route to those sites and they're on the same wireless network! I can ping the sites, but not traceroute to them which I find odd. That I can get through via the iPad implies the problem is with the MBP. In any case, calling M1 support is... not helpful. I get the same behaviour when I bypass the Airport Express entirely and plug the MBP directly into the cable modem. Can anybody explain a) how this is even possible and b) how to fix it? mella:~ ratkins$ ping ajax.googleapis.com PING googleapis.l.google.com (209.85.132.95): 56 data bytes 64 bytes from 209.85.132.95: icmp_seq=0 ttl=50 time=11.488 ms 64 bytes from 209.85.132.95: icmp_seq=1 ttl=53 time=13.012 ms 64 bytes from 209.85.132.95: icmp_seq=2 ttl=53 time=13.048 ms ^C --- googleapis.l.google.com ping statistics --- 3 packets transmitted, 3 packets received, 0.0% packet loss round-trip min/avg/max/stddev = 11.488/12.516/13.048/0.727 ms mella:~ ratkins$ traceroute ajax.googleapis.com traceroute to googleapis.l.google.com (209.85.132.95), 64 hops max, 52 byte packets traceroute: sendto: No route to host 1 traceroute: wrote googleapis.l.google.com 52 chars, ret=-1 *traceroute: sendto: No route to host traceroute: wrote googleapis.l.google.com 52 chars, ret=-1 ^C mella:~ ratkins$ The traceroute from the iPad goes (and I'm copying this by hand): 10.0.1.1 119.56.34.1 172.20.8.222 172.31.253.11 202.65.245.1 202.65.245.142 209.85.243.156 72.14.233.145 209.85.132.82 From the MBP, I can't traceroute to any of the IPs from 172.20.8.222 onwards. [For extra flavour, not being able to access the above appears to stop me logging in to Server Fault via OpenID and formatting the above traceroutes correctly. Anyone with sufficient rep here to do so, I'd be much obliged.]

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• Troubleshooting loss of network connectivity in Windows 2003 - What else to check?

  - by Benny

  We are facing a weird problem in our data center. Our Backup server (running EMC Networker) loses network connection every alternate day around 3:00 AM (Backup schedule starts at midnight). After 2 hours of outage, the network connectivity recovers automatically and back to normal. What we observed: It is unlikely to be network issue, since it is directly connected to server farm switch (layer 2 connection without any intermediate hops). Further, the server is connected to two different switches for Load balancing using Broadcomm Teaming. a) If it were a switch related issue it is unlikely that both the network ports go down, since they are connected to different switch. b) A possibility Vlan wide issue is also ruled out since other devices in the same Vlan are fine. c) Switch interface status is always up. But there are lot of packet drops during the outage period - Can be attributed to high interface utilization of the backup server (near 100%) d) Connectivity is restored without any change on network. Next suspect is resource utilization on Windows server. Both CPU and Memory have rarely exceeded 80%, but NIC card utilization is alarmingly high (near 100%) Not really sure how to investigate this?

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• How to route to a secondary interface on the same physical ethernet?

  - by sjose3612611

  INTERNET<->(wan)BRIDGED_DEVICE(lan)<->ETH_ROUTER<->LAN Problem: Need to access web server on BRIDGED_DEVICE's LAN from INTERNET via ROUTER (BRIDGED_DEVICE's web server cannot be accessed form INTERNET since it has no Public management IP). Cannot configure bridged device. It has a static IP on its LAN to which its web server binds. Attempt: Create a secondary/alias WAN Interface on ETH_ROUTER (e.g Primary: eth0.1 (for internet access) and Secondary: eth0.2 (for accessing web server on BRIDGED_DEVICE), (No VLANs). eth0.1 has a public IP; eth0.2 has a static private IP in the BRIDGED_DEVICE's subnet (e.g 10.0.X.Y). Iptables on ETH_ROUTER: Added a port forward (DNAT) from eth0.1 to eth0.2: iptables -t nat -I PREROUTING -i eth0.1 -p tcp --dport 80 -j DNAT --to-destination 10.0.X.Y iptables -t nat -I POSTROUTING -o eth0.2 -s 10.0.X.0/24 -j MASQUERADE Stateful firewall w/ overall drop policy on FORWARD chain, hence: iptables -I FORWARD -i eth0.1 -d 10.0.X.Y -p tcp --dport 80 -j ACCEPT Can ping from ETH_ROUTER to BRIDGED_DEVICE but unable to reach the web server from Internet. I see packet cont increasing for the DNAT rule but not sure where it disappears in the ETH_ROUTER after that. ETH_ROUTER is the only device that can be configured to achieve this. If familiar with this scenario, please suggest what I may be missing or doing wrong here or suggest techniques to debug?

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• Event Log "Wake Source" when system wakes from sleep

  - by Doltknuckle

  So I've been troubleshooting sleep timers for our systems and have run across an interesting issue. I need a way to report how long a system was awake after a number of different inputs. Now, I've discovered that the System Log tracks wake and sleep events and even tells you the times that everything happens at. The thing is doesn't tell you is what triggered the wake event. It does give you a numerical code however. Here are some examples of what I am finding. Index : 2901 EntryType : Information InstanceId : 1 Message : The system has resumed from sleep. Sleep Time: 2010-10-01T23:20:06.097488100Z Wake Time: 2010-10-03T17:41:12.796400500Z Wake Source: 0 Category : (0) CategoryNumber : 0 Source : Microsoft-Windows-Power-Troubleshooter -- Index : 2841 EntryType : Information InstanceId : 1 Message : The system has resumed from sleep. Sleep Time: 2010-10-01T19:19:37.239789600Z Wake Time: 2010-10-01T21:28:48.921200800Z Wake Source: 4HID Keyboard Device Category : (0) CategoryNumber : 0 Source : Microsoft-Windows-Power-Troubleshooter So here's my question: Does anyone know what the different numerical codes for the "Wake Source" mean? I think "0" is a magic packet and "4" is a USB device. Does anyone have any idea if there is any documentation out there on this for Windows 7? Thanks in advance

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• publickey authentication only works with existing ssh session

  - by aaron

  publickey authentication only works for me if I've already got one ssh session open. I am trying to log into a host running Ubuntu 10.10 desktop with publickey authentication, and it fails when I first log in: [me@my-laptop:~]$ ssh -vv host ... debug1: Next authentication method: publickey debug1: Offering public key: /Users/me/.ssh/id_rsa ... debug2: we did not send a packet, disable method debug1: Next authentication method: password me@hosts's password: And the /var/log/auth.log output: Jan 16 09:57:11 host sshd[1957]: reverse mapping checking getaddrinfo for cpe-70-114-155-20.austin.res.rr.com [70.114.155.20] failed - POSSIBLE BREAK-IN ATTEMPT! Jan 16 09:57:13 host sshd[1957]: pam_sm_authenticate: Called Jan 16 09:57:13 host sshd[1957]: pam_sm_authenticate: username = [astacy] Jan 16 09:57:13 host sshd[1959]: Passphrase file wrapped Jan 16 09:57:15 host sshd[1959]: Error attempting to add filename encryption key to user session keyring; rc = [1] Jan 16 09:57:15 host sshd[1957]: Accepted password for astacy from 70.114.155.20 port 42481 ssh2 Jan 16 09:57:15 host sshd[1957]: pam_unix(sshd:session): session opened for user astacy by (uid=0) Jan 16 09:57:20 host sudo: astacy : TTY=pts/0 ; PWD=/home/astacy ; USER=root ; COMMAND=/usr/bin/tail -f /var/log/auth.log The strange thing is that once I've got this first login session, I run the exact same ssh command, and publickey authentication works: [me@my-laptop:~]$ ssh -vv host ... debug1: Server accepts key: pkalg ssh-rsa blen 277 ... [me@host:~]$ And the /var/log/auth.log output is: Jan 16 09:59:11 host sshd[2061]: reverse mapping checking getaddrinfo for cpe-70-114-155-20.austin.res.rr.com [70.114.155.20] failed - POSSIBLE BREAK-IN ATTEMPT! Jan 16 09:59:11 host sshd[2061]: Accepted publickey for astacy from 70.114.155.20 port 39982 ssh2 Jan 16 09:59:11 host sshd[2061]: pam_unix(sshd:session): session opened for user astacy by (uid=0) What do I need to do to make publickey authentication work on the first login? NOTE: When I installed Ubuntu 10.10, I checked the 'encrypt home folder' option. I'm wondering if this has something to do with the log message "Error attempting to add filename encryption key to user session keyring"

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• Per connection bandwidth limit

  - by Kyr

  Apparently, our server box running Windows Server 2008 R2 has a per connection bandwidth limit of 0.2 MB/s. Meaning, while one TCP connection can pull at max 0.2 MB/s, 60 parallel connections can pull 12 MB/s. We first noticed this when trying to checkout large SVN repository from this server. I used a simple Java application to test this, transferring data from server to workstation using variable number of threads (one connection per thread). Server part of the application simply writes 1 MB memory buffer to socket 100 times, so there is no disk involvement. Each connection topped at 0.2 MB/s. Same per connection limit was for only one as was for 60 parallel connections. The problem is that I have no idea from where this limit comes from. I have very little experience administrating Windows Server, so I was mostly trying to find something by googling. I have checked the following: Local Computer Policy QoS Packet Scheduler Limit reservable bandwidth: it's Not configured; Group Policy Management Console: we have two GOPs, but neiher has any Policy-based QoS defined; There isn't any bandwidth limiter program installed, as far as I can tell. We're using standard Windows Firewall. I can update this question with any additional information if needed.

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• How does Windows 7 DNS client work?

  - by Mark Allison

  I am using a local DHCP and DNS server on my home network on a linux machine. It is running CentOS 6.3 with dnsmasq 2.48. It's all working fine except for local DNS lookups for Windows machines only. I have a mix of Ubuntu, CentOS and Windows machines on the network, some virtual, some physical. I have a machine called boron and the domain is called localdomain If I ping boron from any linux machine, I get [root@lithium lists]# ping -c3 boron PING boron.localdomain (10.0.0.5) 56(84) bytes of data. 64 bytes from boron.localdomain (10.0.0.5): icmp_seq=1 ttl=64 time=0.740 ms 64 bytes from boron.localdomain (10.0.0.5): icmp_seq=2 ttl=64 time=0.478 ms 64 bytes from boron.localdomain (10.0.0.5): icmp_seq=3 ttl=64 time=0.458 ms --- boron.localdomain ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2000ms rtt min/avg/max/mdev = 0.458/0.558/0.740/0.131 ms If I do it from my Windows 7 machine, I get: Ping request could not find host boron. Please check the name and try again. If I try ping boron.localdomain I get: Pinging boron.localdomain [67.215.65.132] with 32 bytes of data: Reply from 67.215.65.132: bytes=32 time=16ms TTL=57 Reply from 67.215.65.132: bytes=32 time=188ms TTL=57 Reply from 67.215.65.132: bytes=32 time=15ms TTL=57 Reply from 67.215.65.132: bytes=32 time=14ms TTL=57 Ping statistics for 67.215.65.132: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 14ms, Maximum = 188ms, Average = 58ms which is clearly wrong. Why is it going out to the internet? Why can't my windows machine resolve the boron hostname to a FQDN? My Windows machines and linux machines get their network config from DHCP. UPDATE If I do ipconfig /all in Windows, it looks as I would expect: Windows IP Configuration Host Name . . . . . . . . . . . . : lanthanum Primary Dns Suffix . . . . . . . : Node Type . . . . . . . . . . . . : Hybrid IP Routing Enabled. . . . . . . . : No WINS Proxy Enabled. . . . . . . . : No DNS Suffix Search List. . . . . . : .localdomain Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : .localdomain Description . . . . . . . . . . . : Realtek PCIe GBE Family Controller Physical Address. . . . . . . . . : 50-E5-49-38-FC-A2 DHCP Enabled. . . . . . . . . . . : Yes Autoconfiguration Enabled . . . . : Yes IPv4 Address. . . . . . . . . . . : 10.0.0.57(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.255.0 Lease Obtained. . . . . . . . . . : 23 August 2012 13:58:45 Lease Expires . . . . . . . . . . : 24 August 2012 07:58:48 Default Gateway . . . . . . . . . : 10.0.0.6 DHCP Server . . . . . . . . . . . : 10.0.0.6 DNS Servers . . . . . . . . . . . : 10.0.0.6 208.67.222.222 208.67.220.220 NetBIOS over Tcpip. . . . . . . . : Enabled When I do an nslookup I get: Server: carbon.localdomain Address: 10.0.0.6 *** carbon.localdomain can't find boron: Unspecified error However if I do ifconfig -a in Linux I get: [root@nitrogen ~]# ifconfig -a eth0 Link encap:Ethernet HWaddr 00:0C:29:AF:EC:2A inet addr:10.0.0.7 Bcast:10.0.0.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:187687 errors:0 dropped:0 overruns:0 frame:0 TX packets:5857 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:23910700 (22.8 MiB) TX bytes:712964 (696.2 KiB) 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:329894 errors:0 dropped:0 overruns:0 frame:0 TX packets:329894 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:67153143 (64.0 MiB) TX bytes:67153143 (64.0 MiB) and nslookup: [root@nitrogen ~]# nslookup boron Server: 10.0.0.6 Address: 10.0.0.6#53 Name: boron Address: 10.0.0.5 Both machines are on the same network using the same DHCP server. UPDATE 2 I thought the issue was resolved but I am getting intermittent DNS resolving issues but only on my Windows 7 machine. All my linux boxes are fine. This is what happens when I ping and nslookup from Windows to a Windows 2008 Server: C:\Users\mark>nslookup magnesium Server: carbon.localdomain Address: 10.0.0.6 Name: magnesium.localdomain Address: 10.0.0.12 C:\Users\mark>ping magnesium Pinging magnesium.localdomain [67.215.65.132] with 32 bytes of data: Reply from 67.215.65.132: bytes=32 time=267ms TTL=57 Reply from 67.215.65.132: bytes=32 time=162ms TTL=57 Reply from 67.215.65.132: bytes=32 time=510ms TTL=57 Reply from 67.215.65.132: bytes=32 time=146ms TTL=57 Ping statistics for 67.215.65.132: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 146ms, Maximum = 510ms, Average = 271ms And from Linux: [root@beryllium ~]# ping -c4 magnesium PING magnesium.localdomain (10.0.0.12) 56(84) bytes of data. 64 bytes from magnesium.localdomain (10.0.0.12): icmp_seq=1 ttl=128 time=0.176 ms 64 bytes from magnesium.localdomain (10.0.0.12): icmp_seq=2 ttl=128 time=0.634 ms 64 bytes from magnesium.localdomain (10.0.0.12): icmp_seq=3 ttl=128 time=0.685 ms 64 bytes from magnesium.localdomain (10.0.0.12): icmp_seq=4 ttl=128 time=0.263 ms --- magnesium.localdomain ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3002ms rtt min/avg/max/mdev = 0.176/0.439/0.685/0.223 ms [root@beryllium ~]# nslookup magnesium Server: 10.0.0.6 Address: 10.0.0.6#53 Name: magnesium.localdomain Address: 10.0.0.12 UPDATE 3 I stopped the Windows DNS client on my Windows 7 machine with net stop dnscache and it is now working fine. It would be nice to get DNS working with the DNS client on, but I might be OK without it, what do you think?

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• FreeRADIUS Default Answer

  - by jinanwow

  We are using FreeRADIUS with a MySQL database, authenticating users. We ran into an issue where are MySQL database was slow causing the max number of threads to be reached. The issue with this is, when the server couldn't answer the requests as there were no threads avaiable, it sent the response of Access-Reject to the clients. Our devices cache client connections and periodically checks with the server to see if they should still be allowed or to remove them. The equipment is designed that if there is no response from the server and a client is connected it will remain connected. The issue is, when the radius server is at its max threads, its default answer is to send access-reject (verified via packet capture), however we would like to change the default behavior to just ignore the request (keeping the clients connected). We have fixed the MySQL database issue for now, but I would like to change the default from Access-Reject, to just ignore the client altogeather. I have done research, but not able to find an answer to the question. Thanks in Advance.

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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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• Guest can't access host windows network share

  - by Asteroza

  HI folks, I've recently run into a strange problem after upgrading to VMware player 3. Certain virtual machines (currently an XP and a VIsta VM) seem to have lost the ability to access the host (XP) network shared folders (SMB). Both VM machines are bridged networking, firewall is up. Host firewall is up. Host and guests use DHCP. All OS are workgroup connected. The Vista VM I am not completely sure, but the XP VM did have access to the host's network shared folders after the player upgrade. Then today it wouldn't work, network path can't be found. Now here's the wierd part. The host's network shared folders can be accessed properly by other PC's on the network (and as far as I know, no settings have been changed). The host is pingable from the guests, and name resolution works. The guests can access network shares on other PC's in the network, and access the internet. My Network Places shows the host PC, but double clicking on it takes a long time before it finally times out with an error. Doing a wireshark packet capture, the guest is sending out the protocol negotiation, and the host is sending a response, but after that the guest behaves like it didn't receive anything and is doing TCP retransmissions. Anybody have any idea what could be wrong? Yes I know I can drag and drop files or setup the special VMware shared folders, but I want to access the host just like any other network accessible shared folder. It just seems really odd when any other computer works, just not between the guest and host.

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• iptables forwarding to a dummy interface

  - by madinc

  Hi, I'm trying to accomplish the following: I have a box with a service listening on a dummy interface (say 172.16.0.1), udp port 5555. Now what I'd like to do is to take packets that arrive on interfaces eth0 (1.1.1.1:5555) and eth1 (2.2.2.2:5555) and forward them to the service on the dummy interface, and have replies go back to clients out the same physical interface they came in. Clients must think they're talking to 1.1.1.1:5555 or 2.2.2.2:5555. I think I need a mix of iptables rules and packet marking, plus some iproute rules (if it's possible at all). What I tried is to catch packets coming in from eth0 and eth1, udp port 5555, and mark them with 1 and 2 respectively, and --save-mark in the connmark. Then I used a DNAT to 172.16.0.1. The service seems to be getting the packets. Now I'm not sure how to do the reverse. It seems that for packets originating from the box, you can't do anything before the routing decision, but that would be the place to restore the marks, and thus make a routing decision based on those. Here's what I have so far: iptables -t mangle -A PREROUTING -d 1.1.1.1 -p udp --port 5555 -j MARK --set-mark 1 iptables -t mangle -A PREROUTING -d 2.2.2.2 -p udp --port 5555 -j MARK --set-mark 2 iptables -t mangle -A PREROUTING -d 1.1.1.1 -p udp --port 5555 -j CONNMARK --save-mark iptables -t mangle -A PREROUTING -d 2.2.2.2 -p udp --port 5555 -j CONNMARK --save-mark iptables -t nat -A PREROUTING -m mark --mark 1 -j DNAT --to-destination 172.16.0.1 iptables -t nat -A PREROUTING -m mark --mark 2 -j DNAT --to-destination 172.16.0.1 # What next? As I said, I'm not even sure it can be done. To give a bit of background, it's an old OpenVPN installation that cannot be upgraded (otherwise I'd install a recent version that supports multihoming natively). Thanks for any help.

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• Windows 2008 R2 Servers Sending Arp Requests for IPs outside Subnet

  - by Kyle Brandt

  By running a packet capture on my my routers I see some of my servers sending ARP requests for IPs that exist outside of its network. For example if my network is: Network: 8.8.8.0/24 Gateway: 8.8.8.1 (MAC: 00:21:9b:aa:aa:aa) Example Server: 8.8.8.20 (MAC: 00:21:9b:bb:bb:bb) By running a capture on the interface that has 8.8.8.1 I see requests like: Sender Mac: 00:21:9b:bb:bb:bb Sender IP: 8.8.8.20 Target MAC: 00:21:9b:aa:aa:aa Target IP: 69.63.181.58 Anyone seen this behavior before? My understanding of ARP is that requests should only go out for IPs within the subnet... Am I confused in my understanding of ARP? If I am not confused, anyone seen this behavior? Also, these seem to happen in bursts and it doesn't happen when I do something like ping an IP outside of the network. Update: In response to Ian's questions. I am not running anything like Hyper-V. I have multiple interfaces but only one is active (Using BACS failover teaming). The subnet mask is 255.255.255.0 (Even if it were something different it wouldn't explain an IP like 69.63.181.58). When I run MS Network Monitor or wireshark I do not see these ARP requests. What happens is that on the router capturing I see a burst of about 10 requests for IPs outside of the network from the host machine. On the machine itself using wireshark or NetMon I see a flood of ARP responses for all the machines on the network. However, I don't see any requests in the capture asking for those responses. So it seems like maybe it is maybe refreshing the arp cache but including IPs that outside of the network. Also when it does this NetMon doesn't show the ARP requests?

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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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• DNS issue on Fedora 12? wget wordpress.org fails where wget www.google.com works

  - by Tom Auger

  I'm administering a Fedora 12 box, but am quite new to networking specifics. Recently one of our WordPress apps hosted on our server has stopped being able to perform its auto-update or auto-download of plugins. Investigating further, I have tried the following: $ wget wordpress.org --2010-12-17 11:26:50-- http://wordpress.org/ Resolving wordpress.org... failed: Temporary failure in name resolution. wget: unable to resolve host address âwordpress.orgâ Whereas: $ wget www.google.com --2010-12-17 11:27:26-- http://www.google.com/ Resolving www.google.com... 74.125.226.82, 74.125.226.84, 74.125.226.80, ... Connecting to www.google.com|74.125.226.82|:80... connected. HTTP request sent, awaiting response... 302 Found Location: http://www.google.ca/ [following] --2010-12-17 11:27:26-- http://www.google.ca/ Resolving www.google.ca... 173.194.32.104 Connecting to www.google.ca|173.194.32.104|:80... connected. HTTP request sent, awaiting response... 200 OK Length: unspecified [text/html] Saving to: âindex.html.4â [ <=> ] 9,079 --.-K/s in 0.02s 2010-12-17 11:27:26 (462 KB/s) - âindex.html.4â Interestingly: $ ping wordpress.org PING wordpress.org (72.233.56.138) 56(84) bytes of data. 64 bytes from wordpress.org (72.233.56.138): icmp_seq=1 ttl=50 time=81.5 ms 64 bytes from wordpress.org (72.233.56.138): icmp_seq=2 ttl=50 time=67.3 ms ^C --- wordpress.org ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1783ms rtt min/avg/max/mdev = 67.361/74.448/81.536/7.092 ms and $ nslookup wordpress.org Server: 192.168.2.1 Address: 192.168.2.1#53 Non-authoritative answer: Name: wordpress.org Address: 72.233.56.138 Name: wordpress.org Address: 72.233.56.139 nscd has been stopped and flushed. iptables appear to be clean. At this point I have exhausted my limited abilities to diagnose the issue. Can anyone suggest a resolution path?

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• iptables advanced routing

  - by Shamanu4

  I have a Centos server acting as a NAT in my network. This server has one external (later ext1) interface and three internal (later int1, int2 and int3). Egress traffic comes from users via int1 and after MASQUERADE goes via ext1. Ingress traffic comes from ext1, MASQUERADE, and goes via int2 or int3 according to static routes. | ext1 | x.x.x.x/24 +---------|----------------------+ | | | Centos server (NAT) | | | +---|------|---------------|-----+ | | | int1 | | int2 | int3 10.30.1.10/24 | | 10.30.2.10/24 | 10.30.3.10/24 ^ v v 10.30.1.1/24 | | 10.30.2.1/24 | 10.30.3.1/24 +---|------|---------------|-----+ | | | | | | | v v | | ^ -Traffic policer- | | |_____________ | | | | | +------------------|-------------+ | 192.168.0.1/16 | | Clients 192.168.0.0/16 The problem: Egress traffic seems to be dropped after PREROUTING table. Packet counters are not changing on MASQUERADE rule in POSTROUTING. If I change the routes to clients causing the traffic go back via int1 - everything works perfectly. current iptable configuration is very simple: # cat /etc/sysconfig/iptables *filter :INPUT ACCEPT [0:0] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [0:0] -I INPUT 1 -i int1 -j ACCEPT -A FORWARD -j ACCEPT COMMIT *nat -A POSTROUTING -o ext1 -j MASQUERADE # COMMIT Can anyone point me what I'm missing? Thanks. UPDATE: 192.168.100.60 via 10.30.2.1 dev int2 proto zebra # routes to clients ... 192.168.100.61 via 10.30.3.1 dev int3 proto zebra # ... I have a lot of them x.x.x.0/24 dev ext1 proto kernel scope link src x.x.x.x 10.30.1.0/24 dev int1 proto kernel scope link src 10.30.1.10 10.30.2.0/24 dev int2 proto kernel scope link src 10.30.2.10 10.30.3.0/24 dev int3 proto kernel scope link src 10.30.3.10 169.254.0.0/16 dev ext1 scope link metric 1003 169.254.0.0/16 dev int1 scope link metric 1004 169.254.0.0/16 dev int2 scope link metric 1005 169.254.0.0/16 dev int3 scope link metric 1006 blackhole 192.168.0.0/16 default via x.x.x.y dev ext1 Clients have 192.168.0.1 as gateway, which is redirecting them to 10.30.1.1

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• What is the replacement of the floppy

  - by alexanderpas

  While CD (and to an lesser extend DVD) disks have reached the price-point of the floppy, they have one significant downside, it is WORM (Write-Once Read-Many) media, allowing it to be used only one single time, and you need to be explicit in writing the data to the actual media (you need to burn it.) While CD-RW solves the "use only once" problem, it is still EWORM (Erasable Write-Once Read-Many) media, which still means you need to be explicit in writing the data to the actual media (you still need to burn it.), and also, you still need to be very explicit in erasing it. (simple delete is not possible.) Okay, we can use a CD-RW in Packet Writing mode, however the downside to that, is that this mode is not very universal, and also, not the native mode of the media. Now, while USB-sticks and SD-cards may not have the poblems of the CD, they have a whole other kind of problem: their PRICE! USB-sticks and SD cards are generally 10 to 100 times as expensive as diskettes per piece. SD-cards, in addition have an added problem, because they need a reader to operate. While it is a very standard thing, it is not default equipment on the computer like the CD drive or USB port (or historically the diskette drive). You wouldn't give out an USB stick or SD card with a 100 kB text file, not caring weither you would get it back or not. So, to recap: CD & DVD are basically WORM media. SD cards and USB sticks are relatively expensive. SD cards also needs special readers. Diskettes have a very low data-rate Diskettes have a very low storage capacity. Now, is there a media out there that solves all these problems, or is there a way to get (very) small USB sticks or SD cards for a very low price (as they're the closest thing to diskette).

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• Transparent proxying leaves sockets with SYN_RCVD in MacOS X 10.6 Snow Leopard (and maybe FreeBSD)

  - by apenwarr

  I'm trying to create a transparent proxy on my MacOS machine in order to port the sshuttle ssh-based transproxy VPN from Linux. I think I almost have it working, but sadly, almost is not 100%. Short version is this. In one window, start something that listens on port 12300: $ while :; do nc -l 12300; done Now enable proxying: # sysctl -w net.inet.ip.forwarding=1 # sysctl -w net.inet.ip.fw.enable=1 # ipfw add 1000 fwd 127.0.0.1,12300 log tcp from any to any And now test it out: $ telnet localhost 9999 # any port number will do # this works; type stuff and you'll see it in the nc window $ telnet google.com 80 # any host/port will do # this *doesn't* work! After the latter experiment, I see lines like this in netstat: $ netstat -tn | grep ^tcp4 tcp4 0 0 66.249.91.104.80 192.168.1.130.61072 SYN_RCVD tcp4 0 0 192.168.1.130.61072 66.249.91.104.80 SYN_SENT The second socket belongs to my telnet program; the first is more suspicious. SYN_RCVD implies that my SYN packet was correctly captured by the firewall and taken in by the kernel, but apparently the SYNACK was never sent back to telnet, because it's still in SYN_SENT. On the other hand, if I kill the nc server, I get this: $ telnet google.com 80 Trying 66.249.81.104... telnet: connect to address 66.249.81.104: Connection refused telnet: Unable to connect to remote host ...which is as expected: my proxy server isn't running, so ipfw redirects my connection to port 12300, which has nobody listening on it, ie. connection refused. My uname says this: $ uname -a Darwin mean.local 10.2.0 Darwin Kernel Version 10.2.0: Tue Nov 3 10:37:10 PST 2009; root:xnu-1486.2.11~1/RELEASE_I386 i386 Does anybody see any different results? (I'm especially interested in Snow Leopard vs Leopard results, as there seem to be some internet rumours that transproxy is broken in Snow Leopard version) Any advice for how to fix?

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• Is timeout in tracertoutput an indication of an error?

  - by nitramk

  TCP/IP packages sent from my computer to a remote server does not always reach destination and ends up being retransmitted sometimes several times before they succeed. To troubleshoot this, I'm running a tracert to the server: Tracing route to <site> [<address>] Over a maximum of 30 hops: 1 <1 ms <1 ms <1 ms mymachine 2 <1 ms <1 ms <1 ms gw.levonline.com [217.70.32.30] 3 <1 ms <1 ms <1 ms 81.201.213.218 4 <1 ms <1 ms <1 ms bmf1-hmf1.driften.net [81.201.213.12] 5 <1 ms <1 ms <1 ms 10ge-2-4-cr2.a1.sth.ownit.se [84.246.88.157] 6 <1 ms * <1 ms netnod-ix-ge-b-sth-4470.microsoft.com [195.69.11.181] 7 26 ms * * ge-3-0-0-0.ams-64cb-1a.ntwk.msn.net [207.46.42.1] 8 48 ms 57 ms 56 ms ten9-1.lts-76e-1.ntwk.msn.net [207.46.42.133] 9 * * * Request timed out. In step 6 and 7, I'm seeing timeouts while waiting for the reply from the server (as seen above). Running the same tracert many times gives varying output, sometimes the response is fine, but sometimes I get this timeout 1, 2 and sometimes for all 3 packets. The timeout always starts at the same server, netnod-ix-ge-b-sth-4470.microsoft.com. I've tried setting the tracert timeout to 10 seconds, but am still getting the timeout. Running tracert towards other servers does not give me the same timeout. Microsoft network technicians tells me that the problem is not on "their" side. Are these timeouts an indicator of a lost packet on the specific node which did not respond? Are the timeouts an indication of there being a problem, or is it normal?

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• Window 7 Host does not answer to ping

  - by gencha

  Today I tried printing on a shared printer on one of our homegroup members. Sadly it did not work (printer marked as offline). Shortly after, I noticed I can't even ping the machine that owns the printer (I also can not remotely access it in any other way I've tried). Currently I'm trying to ping the machine from the router both computers are connected to (and my machine in question doesn't answer). I do receive the echo requests (as verified with WireShark). I also added a rule in the Windows Firewall to specifically allow ICMP echo requests, but that didn't change anything. I also tried netsh firewall set icmpsetting 8 enable, but that didn't change anything either. Completely disabling the Windows Firewall has no effect on the issue either. One has to wonder, where does Windows log when and why it ignored any incoming packets? How can I get to the bottom of this? Here are some ways I found to dig deeper into the issue: Enabling logging on the Windows Firewall Enabling Windows Filtering Platform Auditing Both methods at least give more insight into the issue. The plain log file is full of entries like this: 2011-11-11 14:35:27 DROP ICMP 192.168.133.1 192.168.133.128 - - 84 - - - - 8 0 - RECEIVE So the ICMP packets are being dropped as if that was intended. The Event Viewer now gives a little bit more details: The Windows Filtering Platform has blocked a packet. Application Information: Process ID: 4 Application Name: System Network Information: Direction: Inbound Source Address: 192.168.133.1 Source Port: 0 Destination Address: 192.168.133.128 Destination Port: 8 Protocol: 1 Filter Information: Filter Run-Time ID: 214517 Layer Name: Receive/Accept Layer Run-Time ID: 44 This same entry is always repeated with 2 points of information changing: Process ID: 420 Application Name: \device\harddiskvolume2\windows\system32\svchost.exe The service host with the PID 420 is the host for the following services: Windows Audio DHCP Client Windows Event Log HomeGroup Provider TCP/IP NetBIOS Helper Security Center Additionally, there is currently this problem with the same machine: Even though my network is set to be a "Home network", I am unable to create a new homegroup.

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• Bridging my laptop's wireless and wired adaptors

  - by stacey.richards

  I would like to be able to connect a desktop computer that does not have a wireless adapter to my wireless network. I could just run a network cable from my ADSL/wireless router to the desktop computer but sometimes this is not practical. What I would really like to do is bridge my laptop's wireless and wired adapters in such a way that I can run a network cable from my laptop to a switch and another network cable from the switch to a desktop computer so that the desktop computer can access the Internet through my ADSL/wireless router via my latop: +--------------------+ |ADSL/wireless router| +--------------------+ | +-------------------------+ |laptop's wireless adaptor| | | |laptop's wired adaptor | +-------------------------+ | +------+ |switch| +------+ | +-----------------------+ |desktop's wired adapter| +-----------------------+ A bit of Googling suggests that I can do this by bridging my laptop's wireless and wired adapters. In Windows XP's Network Connections I select both the Local Area Connection and the Wireless Network Connection, right click and select Bridge Connections. From what I gather, this (layer 2?) bridge will examine the MAC address of traffic coming from the wireless network and pass it through to the wired network if it suspects that a network adapter with that MAC address may be on the wired side, and vice-versa. If this is the case, I would assume that when the desktop computer attempts to get an IP address from a DHCP server (which is running on the ADSL/wireless router), it would send a DHCP broadcast packet which would pass through the laptop's bridge to the router and the reply would return through the laptop's bridge back to the desktop. This doesn't happen. With some more Googling I find some instruction how this can be done with Linux. I reboot to Ubuntu 9.10 and type the following: sudo apt-get install bridge-utils sudo brctl addbr br0 sudo brctl addif br0 wlan0 sudo brctl addif br0 eth0 sudo ipconfig wlan0 0.0.0.0 sudo ipconfig eth0 0.0.0.0 Once again, the desktop cannot reach the ADSL/wireless router. I suspect that I'm missing some simple important step. Can anyone shed some light on this for me?

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• Is ffmpeg incorrectly interpreting .aif files?

  - by marue

  Being on an Ubuntu 10.04 server i installed the ffmpeg packages with apt. ffmpeg is working afterwards, and doing as it should. Almost. For testing purposes i uploaded a few audiofiles. One of them, an aif file, is not being correctly interpreted. While on my workhorse (Mac SnowLeopard) ffmpeg tells the format as Stream #0.0: Audio: pcm_s24be, 44100 Hz, 2 channels, s32, 2116 kb/s my Ubuntu server says it is: Stream #0.0: Audio: pcm_s24be, 44100 Hz, stereo, s16, 2116 kb/s which is the wrong bitdepth. Ubuntu then fails to convert the file with the error message [pcm_s24be @ 0xcd4b580]invalid PCM packet Error while decoding stream #0.0 which certainly is not true. The file is perfectly valid. Are there any know issues for ffmpeg interpreting the aif format? How can i find out which version of the aif-codec ffmpeg is using? Any ideas how to approach this issue? ffprobe output: FFprobe version SVN-r20090707, Copyright (c) 2007-2009 Stefano Sabatini libavutil 49.15. 0 / 49.15. 0 libavcodec 52.20. 0 / 52.20. 1 libavformat 52.31. 0 / 52.31. 0 built on Jan 20 2010 00:13:01, gcc: 4.4.3 20100116 (prerelease) Input #0, aiff, from 'testfile.aif': Duration: 00:00:04.00, start: 0.000000, bitrate: 2117 kb/s Stream #0.0: Audio: pcm_s24be, 44100 Hz, stereo, s16, 2116 kb/s update 2: Forcing the conversion with -sample_fmt s32 doesn't change anything. Strange thing is: Even without using -sample_fmt s32 i just realized that the conversion is working and creates valid audiofiles. There just is the error message from above.

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• Preventing DDOS/SYN attacks (as far as possible)

  - by Godius

  Recently my CENTOS machine has been under many attacks. I run MRTG and the TCP connections graph shoots up like crazy when an attack is going on. It results in the machine becoming inaccessible. My MRTG graph: mrtg graph This is my current /etc/sysctl.conf config # Kernel sysctl configuration file for Red Hat Linux # # For binary values, 0 is disabled, 1 is enabled. See sysctl(8) and # sysctl.conf(5) for more details. # Controls IP packet forwarding net.ipv4.ip_forward = 0 # Controls source route verification net.ipv4.conf.default.rp_filter = 1 # Do not accept source routing net.ipv4.conf.default.accept_source_route = 0 # Controls the System Request debugging functionality of the kernel kernel.sysrq = 1 # Controls whether core dumps will append the PID to the core filename # Useful for debugging multi-threaded applications kernel.core_uses_pid = 1 # Controls the use of TCP syncookies net.ipv4.tcp_syncookies = 1 # Controls the maximum size of a message, in bytes kernel.msgmnb = 65536 # Controls the default maxmimum size of a mesage queue kernel.msgmax = 65536 # Controls the maximum shared segment size, in bytes kernel.shmmax = 68719476736 # Controls the maximum number of shared memory segments, in pages kernel.shmall = 4294967296 net.ipv4.conf.all.rp_filter = 1 net.ipv4.tcp_syncookies = 1 net.ipv4.icmp_echo_ignore_broadcasts = 1 net.ipv4.conf.all.accept_redirects = 0 net.ipv6.conf.all.accept_redirects = 0 net.ipv4.conf.all.send_redirects = 0 net.ipv4.conf.all.accept_source_route = 0 net.ipv4.conf.all.rp_filter = 1 net.ipv4.tcp_max_syn_backlog = 1280 Futher more in my Iptables file (/etc/sysconfig/iptables ) I only have this setup # Generated by iptables-save v1.3.5 on Mon Feb 14 07:07:31 2011 *filter :INPUT ACCEPT [1139630:287215872] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [1222418:555508541] Together with the settings above, there are about 800 IP's blocked via the iptables file by lines like: -A INPUT -s 82.77.119.47 -j DROP These have all been added by my hoster, when Ive emailed them in the past about attacks. Im no expert, but im not sure if this is ideal. My question is, what are some good things to add to the iptables file and possibly other files which would make it harder for the attackers to attack my machine without closing out any non-attacking users. Thanks in advance!

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