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I segmented a large subnet into smaller VLANs. Running VMware vCenter 5.1 / ESXi 5.1 on the hosts. I run a number of guest VMs, Win28k, Cent, RHEL, and Ubuntu. All hosts except the Ubuntu hosts work without issue. The ubuntu hosts can ping and be pinged over my WAN connection but accessing them remotely via SSH or HTTP hang. Windows hosts on same VLAN vSwitch do not have this problem. vSwitch is not currently tagging, physical switch is dual-mode tagging for the VMs.

I'm out of ideas.

Thanks!

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  • Did you reboot?
    – ewwhite
    Sep 9, 2014 at 14:54
  • Everything, repeatedly.
    – user218983
    Sep 9, 2014 at 15:01
  • Running tcpdump on one of the erring guests while you try to connect (you'll have to use the console obviously) is probably going to show you the issue. Also assuming that you do actually have sshd installed. It isn't by default on Ubuntu :-)
    – Ian Macintosh
    Sep 9, 2014 at 15:07
  • I have a dump of the communication, and it shows tcp retransmissions. I'm not entirely sure how to read it though. SSH is installed. Everything was working before the VLAN migration. Link to my tcpdump: cloud.rs-us.net/…
    – user218983
    Sep 9, 2014 at 15:22

1 Answer 1

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So I found the solution. The problem was MTU size of the upstream router. It was incorrectly configured and the Ubuntu Linux servers were not fragmenting the packets as requested. This command:

tracepath -n $ip_address

shows you the MTU responses from the routers. Once I manually reconfigured my interface with the slowest MTU size data was flowing.

ifconfig $interface mtu $number from tracepath

This is only a work around, these routers must be corrected.

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