[Users] oVirt 3.4 - MTU Override not honoured by virtual NICs

[Mike Kolesnik]

----- Original Message -----
> 
> > This sounds like a reasonable behaviour since there is a clear separation
> > between the host networking configuration to the vms networking
> > configuration.
> > What you're attempting to achieve is guest-os level network configuration
> > which
> > isn't controlled by the ovirt-engine.
> If I understand this correctly the the VMs NIC is mapped to a Virtual
> Nic in the Host with a similar MAC, created when the VM starts.
> 
> # VM internal NIC
> eth1      Link encap:Ethernet  HWaddr 00:1A:4A:2F:D2:A8
>            inet addr:192.168.43.15  Bcast:192.168.43.255 Mask:255.255.255.0
>            inet6 addr: fe80::21a:4aff:fe2f:d2a8/64 Scope:Link
>            UP BROADCAST RUNNING MULTICAST  MTU:9000  Metric:1
>            RX packets:6 errors:0 dropped:0 overruns:0 frame:0
>            TX packets:7 errors:0 dropped:0 overruns:0 carrier:0
>            collisions:0 txqueuelen:1000
>            RX bytes:468 (468.0 b)  TX bytes:578 (578.0 b)
> 
> # Host Virtual Nic
> vnet26    Link encap:Ethernet  HWaddr FE:1A:4A:2F:D2:A8
>            inet6 addr: fe80::fc1a:4aff:fe2f:d2a8/64 Scope:Link
>            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>            RX packets:8 errors:0 dropped:0 overruns:0 frame:0
>            TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
>            collisions:0 txqueuelen:500
>            RX bytes:648 (648.0 b)  TX bytes:468 (468.0 b)

Tap should definitely have the same MTU as the bridge it's started on.

> 
> 
> As you can see the MTU differs between the two. If setting the MTU of
> vnet26 to match the VM;s internal nic (and the host physical NIC for
> that matter), everything is back to normal.
> 
> I'm quite sure that nic (vnet26) must match what is set on the host
> physical NIC, I cant see how it would work otherwise.

You are correct, can you please open a bug for it?
Also please specify libvirt/vdsm/kernel versions that you're using (maybe it was already fixed in updated version?)

> 
> Rgds Jonas
>