[Xen-users] Strange network issue; Guest/DomU outgoing traffic

[eric van blokland <ericvanblokland@xxxxxxxxx>]

Hello all,

I've recently observed some strange behaviour on several DomU (spread
over several xen setups). While I've found a few reports on similar
issues, the discussions were fairly old and discontinued without
providing a cause or solution.

Every once in a while (sometimes with an interval of several months) I
get a "host down" alert for a guest host. The host is actually very
responsive and working fine in every aspect but for the network. Due
to lack of time I reboot those guests and everything is fine again.
(Read on, ofcourse I did some checks to identify the issue but
production servers have to come back up.)

Today a development guest is having exactly the same problem and I
started to investigate. Tcpdump on the guest shows incomming traffic,
however, no outgoing traffic is to be observed:

Arp requests (who-has) are being received, but we never reply.

After manually adding addresses to arp:

ICMP ping/TCP testpackets/UDP testpackets are being received, never replied to.

Trying to ping from the specific guest or sending anything through the
network interface doesn't show up in tcpdump. (writing to the socket
does not give an error)

Things I tried but did nothing:

- Restarting the network (interface).
- Changing the interface hw address.
- Bringing the Dom0 virtual interface down and up again. (As suggested
as temporary fix in an old discussion).

Nothing of interest can be found in any log (for either the guest or Dom0).

This particalur setup is Xen 3.1.? running CentOS5 as Dom0 and DomU
using a network-bridge setup. Other guest(s) running simultaneous on
the same hypervisor continue to work without any (networking) issue.

Does anyone have an idea about the cause or a solution to this problem?

Kind regards and thanks in advance,

Eric

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