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

[Jonas Israelsson]

> 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)


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.

Rgds Jonas