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[Xen-users] arbitrary network unreachable problems

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] arbitrary network unreachable problems
From: samuel <samu60@xxxxxxxxx>
Date: Tue, 29 Sep 2009 13:41:53 +0200
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Hi all,

Recently I've faced a trouble about some networking problem in a Xen server.

debian lenny kernel 2.6.26-1-xen-686 #1 SMP
xen_caps               : xen-3.0-x86_32p

4 domU all the same
debian lenny kernel  2.6.26-1-xen-686 #1 SMP
with 256M memory

dom0 has access to 4 CPUs:
xm vcpu-list
Name                                ID  VCPU   CPU State   Time(s) CPU Affinity
Domain-0                             0     0     1   r--   47960.4 any cpu
Domain-0                             0     1     0   -b-    1531.2 any cpu
Domain-0                             0     2     1   -b-    1335.4 any cpu
Domain-0                             0     3     2   -b-    2513.8 any cpu
firstdomU                            6     0     3   -b-   39686.3 any cpu
seconddomU                          8     0     3   -b-   20195.7 any cpu
thriddomU                        7     0     3   -b-   19494.5 any cpu
fourthdomU                         9     0     3   -b-   20209.4 any cpu

The issue is that 3 out of the 4 domU, randomly appear Network is unreachable problems as if there were no routes to the destinations although there is. The dom0 is acting as a router for all the domains with next option:
(network-script network-multiple-bridge)

dom0 has 2 interfaces, one internal and an external

pings to the destination from domUs works after the Network is unreachable message appear.

ip_conntrack table is not full at dom0:
# cat /proc/net/ip_conntrack | wc -l
# cat /proc/sys/net/ipv4/netfilter/ip_conntrack_max

netperf checks looked ok, showing around 2G throughpout between domUs and between dom0

routes are ok in all the 4 nodes, pointing at dom0 "internal" address.

The most annoying thing is that one domU does not show the problem and the other 3 do....anyone can point any method to check where the problem may reside? I can provide more info because I've tried to make the e-mail not very long and I think I didn't succeed :(

Any hint will be higly appreciated,

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