[Users] Re: Hosts not responding, kinda urgent

[Michael H. Warfield]

On Fri, 2010-02-19 at 20:51 -0800, Gregor at HostGIS wrote: 
> Well, guys, here's a weird one. I fixed it, but you won't believe how.

> I used "vzctl enter" to enter the VE, then "route -n" to see its 
> gateway. Then ping the gateway, and it worked; skipped 1-2 pings, but 
> the pings came back and the VEs were once again visible on the Internet.

> Weird, huh?

Eh...  I don't know.  I've seen it before but MUCH more often with IPv6
in a bridging situation.

> Thing is, I did them one at a time (after the first one, which I was 
> surprised worked) and it's definitely causative here. I sit there 
> pinging from my PC and from our monitoring server, and nothing nothing 
> nothing; then the instant I send 1 ping to the gateway from within the 
> VPS, it comes up. Four VEs in a row did this.

> Any ideas as to what could have caused this "outage" in the first place, 
> and why sending a ping would have fixed it?

Are you using the veth or vnet drivers?  If it's vnet, I don't have a
clue.  I depend on IPv6 for a lot of things and vnet is not IPv6
compliant and generally a pain in my rear any time I've tried to use it
(personal opinion vnet = sucks).  OTOH, veth works very well with
bridging in the host but I have seen this very phenomena you describe,
only mostly with IPv6.  Often it's very transitive.  Bridges tend to
"stall out" as things get added to them and they relearn their MAC
deliveries, but that's usually only seconds.  But I've seen times were
v6 just doesn't work if I don't ping out first.  I THINK (not sure,
honestly) it mostly happens, in that case, were I don't allow the VM to
participate in stateless autoconf and depend on static addressing that
it fails the most often and have static IPv4 addresses as well.

Mike
-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 482 bytes
Desc: This is a digitally signed message part
Url : http://openvz.org/pipermail/users/attachments/20100220/449840c1/attachment.bin