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

["Fischer, Anna" <anna.fischer@xxxxxx>]

> -----Original Message-----
> From: Luke S Crawford [mailto:lsc@xxxxxxxxx]
> Sent: 25 March 2009 17:08
> To: Fischer, Anna
> Cc: eric van blokland; xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Strange network issue; Guest/DomU outgoing
> traffic
> 
> "Fischer, Anna" <anna.fischer@xxxxxx> writes:
> 
> > If you are tracing within DomU, assuming you are doing a simple Linux
> "ping x.x.x.x" command where x.x.x.x is on the same network as your
> DomU, then the only reason that you would not see an ICMP packet would
> be that you do not have an ARP table entry for x.x.x.x on DomU. What
> does your ARP table show? If there is no entry, then you should see an
> ARP packet in the trace. If you do not see an ARP packet, then it could
> be that your routing is not set up properly. What does ip route show?
> 
> ip route (well, I used netstat -rn)  showed the correct things.   my
> default
> gateway was on the same network as the netmask of eth0, and netstat -rn
> showed
> that.   the arp table had an unresolved entry for the default gateway
> and
> nothing else.  deleting that entry and trying again would not
> incerement
> the tx packet count even by 1.
> 
> I even tried arping the default gateway.  

I guess you mean you do "arp -d x.x.x.x", and then "ping x.x.x.x", or "arping 
x.x.x.x" where x.x.x.x is configured as your default gateway? That should 
definitely cause an ARP request to go out. You do not have any weird 
arpd/kernel configuration enabled?

Also, you do not have any weird network setup within your DomU? Like a bridge, 
VLAN bonding, or IP forwarding, or IP aliases, or whatever else?

And, you only have a single interface assigned (and configured!) per virtual 
machine? And you have /proc/sys/net/ipv4/conf/all/arp_filter set to 0?


> the packet counters still
> would not
> increment (and I didn't see any outgoing arp packets)   the syntax was
> right,
> as I try it after reboot (rebooting the DomU not the Dom0)  and I see
> arp
> packets as I would expect.
> 
> when this is happening I ususally leave an inbound ping going from
> another
> host.  I see the packets heading in, nothing (not even an arp who-has)
> going out.

I guess you capture at the interface level with tcpdump, but for incoming 
packets it could also be that they are not received on the higher level, e.g. 
if you have packet filtering enabled or something similar. I guess you are not 
running a firewall or something?
 
> > Do your interface counters / netstat values show any TX errors at
> all?
> 
> None.

Then this would be a failure somewhere in the IP stack, or possibly in the ARP 
kernel code... If you are sure that you have not misconfigured anything, then I 
would probably go for a kernel upgrade... 

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