[Xen-users] VLANs and Networking between DomU and Dom0

[Reinhard Brandstädter <reinhard.brandstaedter@xxxxxx>]

Hello,

I've configured multiple bridges on my Dom0 for VLAN tagged and untagged 
traffic. On the Dom0 I have two physical interfaces and one VLAN interface:
eth0 (untagged)
eth1 (untagged) (network config 192.168.3.10/24)
eth1.1002 (VLAN 1002) (network config 192.168.3.104/24)

Xen creates three bridges in the networking script:
dir=$(dirname "$0")
"$dir/network-bridge" "$@" vifnum=0 netdev=eth0 bridge=xenbr0
"$dir/network-bridge" "$@" vifnum=1 netdev=eth1 bridge=xenbr1
"$dir/network-bridge" "$@" vifnum=2 netdev=eth1.1002 bridge=xenbr1V2

resulting in the bridges:
xenbr0
xenbr1
xenbr1V2

Now I can create two virtual machines that use the 'xenbr1V2' as network 
device (network config 192.168.3.0/24, assigned IP .101 and .103) and those 
machines can see (and communicate/ping) with eachother.
Another virtual machine uses 'xenbr1' as network device (network config 
192.168.3.0/24, assigned IP .102).
As expected it is not possible to ping between the machines on the VLAN bridge 
and the one on the untagged bridge.

However I can't ping the Dom0 from the VLAN tagged machines but I can from the 
untagged machines (and vice versa).
I assumed that this might have something to do with routing (since i use the 
same network/mask on both nets (tagged and untagged).
So I checked with the routing table.

with this table i can ping the untagged VM:
Kernel IP routing table
Destination  Gateway     Genmask         Flags Metric Ref    Use Iface
xxx.xx.x.x   0.0.0.0     255.255.255.0   U     0      0        0 eth0
192.168.3.0  0.0.0.0     255.255.255.0   U     0      0        0 eth1
0.0.0.0      xxx.xx.x.x  0.0.0.0         UG    0      0        0 eth0

With this table I expected to be able to ping the tagged VM but couldn't:
Kernel IP routing table
Destination  Gateway     Genmask         Flags Metric Ref    Use Iface
xxx.xx.x.x   0.0.0.0     255.255.255.0   U     0      0        0 eth0
192.168.3.0  0.0.0.0     255.255.255.0   U     0      0        0 eth1.1002
0.0.0.0      xxx.xx.x.x  0.0.0.0         UG    0      0        0 eth0

This might not even be a Xen specific issue but maybe anyone here has/had a 
similar configuration and might point me in the right direction.

Thanks,
Reinhard

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