[Xen-users] arbitrary network unreachable problems

samuel
Tue, 29 Sep 2009 11:41:53 -0000

Hi all,

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

dom0
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
1744
# cat /proc/sys/net/ipv4/netfilter/ip_conntrack_max
65536

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,
Samuel.


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