I have an EC2 instance (in eu-west-1) which I've been SSH'ing into for almost a year, but recently the connection simply hangs (i.e. becomes fully unresponsive) when an executed command returns more than ~10 lines of output (i.e. htop or ls -la etc.).

So far I've tried -

1) Using the -vvvv switch against ssh

No debug info of any use is shown. If I leave the connection idle I can see keepalives being sent for as long as the ClientAlive param (360/10mins I believe). As soon as a big command is executed, there is no output.

2) The sshd logfile shows that the client sent a SIGCHLD signal to terminal the connection

Excerpt from logfile here - http://pastebin.com/EUwxFqC5

I have noticed that if I ssh into my other VPS (not in AWS) and then ssh into EC2, everything works fine. I can only assume there's something up with my works network, which is dropping the connection, but I'm not sure where to begin debugging this.

If I fire up a brand new instance in us-west-1 (N. Cali) and try all this again, exactly the same behavior is seen as with eu-west-1. This reasserts that my work network is at fault, but only for EC2 for some reason.

Traceroute from my work network to my EC2 instance hangs as soon as it hits the first public ipv6 address from amazon. This is observed from ~6 computers on the same network (all the same behaviour). If I try this from my macbook on an external network, everything works as intended and the traceroute hops through approx. 4 EC2 servers before hitting my instance.

Any ideas? Thanks!

  • Your work network, are you using some sort of 4to6 tunnels?
    – NickW
    Commented Feb 14, 2014 at 12:14
  • I'm not sure, but I'll ask our actual IT guys (external).
    – njt
    Commented Feb 14, 2014 at 12:39
  • ah. test-ipv6.com gives our network 0/10 for ipv6 readiness. it def used to work. someone must have broken/changed something...
    – njt
    Commented Feb 14, 2014 at 12:39
  • Yeah, in the meantime, you might want to try and connect to the IPv4 EC2 instances until they sort it out.
    – NickW
    Commented Feb 14, 2014 at 12:45
  • It appears our new ISP doesn't support IPv6 yet (I wasn't aware we changed ISP...). My EC2 instance is sat behind an IPv4 address, but with an IPv6 public DNS. I'm assuming this may be the root of my issue?
    – njt
    Commented Feb 14, 2014 at 13:14


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