[CentOS-virt] kvm: centos 7 guest on centos 6 host network problems

Mon May 23 10:50:01 UTC 2016
Matthias Leopold <matthias at leopold.priv.at>


i'm rather new to kvm. now i set up a centos 7 guest on a centos 6 kvm 

when i try to use bridged networking in the centos7 guest this works for 
the interface that uses eth1/br1 on the host. when i try to use a second 
interface in the guest with eth0/br0 on the host this brings the host 
interface down as soon as i do ip configuration in the guest (so it 
seems). eth0 shall have the default route in host and guest. three other 
centos 6 guests (not set up by me) use both interfaces in bridged mode 
with no problems.

both interfaces on the host are intel cards (e1000e). driver in the kvm 
guest configuration is "virtio".

dmesg on the kvm host (centos 6) says:

device vnet9 entered promiscuous mode
br0: port 5(vnet9) entering forwarding state
device vnet10 entered promiscuous mode
br1: port 5(vnet10) entering forwarding state
vnet10: no IPv6 routers present
vnet9: no IPv6 routers present
kvm: 17778: cpu0 disabled perfctr wrmsr: 0xc2 data 0xffff
e1000e: eth0 NIC Link is Down

ethtool -k output differs in "rx-vlan-filter" (off for eth0)
centos 6 kernel is 2.6.32-573.22.1.el6.x86_64

what could be wrong?