[Pkg-xen-devel] Bug#429789: Bug#429789: peth0: received packet with own address as source address

Ralph Passgang rp at trust-it.de
Mon Apr 28 09:33:17 UTC 2008

Zitat von martin f krafft <madduck at debian.org>:

> also sprach Adriaan Peeters <apeeters at lashout.net> [2008.04.25.1648 +0400]:
>> > And we have a virtual interface, called eth0, which should be used if
>> > xen's domain0 wants to communicate via network. eth0 is also part of
>> > this bridge. eth0 should have the mac adress of you real network
>> > interface.
>> This is how I understood the Xen documentation indeed.
> Are you sure that eth0 (a bridge) has to have the actual MAC address
> and not peth0?

eth0 is not "the bridge". the bridge is normally called xenbr0. eth0  
is a virtual interface, connected to xenbr0. peth0 is the physical  
device (eth0 on a non-xen system) and also connected to this bridge.

peth0 has FE:FF:FF:FF:FF:FF as MAC address
xenbr0 also uses FE:FF:FF:FF:FF as MAC address
eth0 has the MAC address of the real interface

> If a bridge br0 has interfaces eth0 and eth1, which MAC address is
> used to communicate on network 0? Which one on network 1? Is it
> br0's or is it eth0/1's?

In our case br0 (on a xen system it's xenbr0) has no ip address. A  
interface without an ip adress cannot be used for generating packets.

Your question for eth0/eth1 is quite easy. It will use the routing  
table for a decission. If there is a routing entry for the  
destination, then it will use this routing information. If there is no  
direct routing info in the routing table, then it will use the default  
route generating new packets.

The bridiging is not relevant at all for layer 3 stuff like routing.  
Linux will use the same logic as on a normal multi-homed system.

This might get more obvious if you think about what a bridge actually  
is. A multiport-bridge (which we have in xen) is like a simple layer 2  
switch. So there is no routing involved, just port switching logic  
which is build on arp/mac.

So, if "fe:ff:ff:ff:ff:ff" can really be observed on the wire, then  
the routing information must be wrong and seems to use peth0 or xenbr0  
instead of eth0. Or eth0 is not configured correctly and has a wrong  
arp adress.

That's why I asked for all the "ip route" information. I guess there  
is something wrong in Adriaan's configuration.

There is also some infos available in the xen wiki:



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