Re: jails bring down network interface

• Previous message: David Adam: "Re: Multiple consumers of /dev/dsp"
• In reply to: Benjamin Lutz: "jails bring down network interface"
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Date: Thu, 21 Jul 2005 14:59:23 +0100 (BST)
To: Benjamin Lutz <benlutz@datacomm.ch>

On Thu, 21 Jul 2005, Benjamin Lutz wrote:

> While tracking an issue with a jail I run, the interface to which the
> jail aliases it's IP to suddenly became unresponsive.
>
> My script starts the jail, then runs ifconfig alias. After starting and
> stopping the jail about 20 times, the interface basically froze.
> Ifconfig reported it as up and running, but it would no longer pass any
> packets. Bringing it down then back up made it work again.
>
> Since this is a production machine, I'm afraid I can't give more
> specific details, I don't wish to run into the problem again.
>
> I'm running FreeBSD 5.4-p5, the interface in question is a VIA VT6105
> Rhine III using the vr(4) driver.

Should this occur again, the starting point to investigate is to determine
whether it's "sending" that's broken, "receiving" that's broken, or both.
I would investigate them by:

- Using ping on the system to ping a remote host, see if the other system
   receives the ping packets using tcpdump.

- Use ping on another host to ping the local host, and see if tcpdump on
   the local host sees the ping packets.

As an FYI, ideally you'll do it using a pair of machines that already have
each other in the ARP cache, or otherwise you'll need to look for ARP
requests on the local area network instead of ICMP requests. Beware
switches and routers that mask traffic from third parties (hence
suggesting using those two machines).

Also, it would be good to know if the if_vr interface receives interrupts
or not when it's "wedged" -- you can check this using vmstat -i or systat
-vmstat 1 and see what the interrupt count for the interface is. I prefer
systat to vmstat, FYI.

Finally, if you sit there and ping for a while, do you start getting
ENOBUFS back from the interface?

Finally, the dmesg probe output would be helpful.

Thanks,

Robert N M Watson
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• Previous message: David Adam: "Re: Multiple consumers of /dev/dsp"
• In reply to: Benjamin Lutz: "jails bring down network interface"
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