Re: [Users] oVirt 3.4 - MTU Override not honoured by virtual NICs
----- Original Message -----
From: "Jonas Israelsson" <jonas(a)israelsson.com>
To: users(a)ovirt.org
Sent: Saturday, March 1, 2014 3:28:15 PM
Subject: [Users] oVirt 3.4 - MTU Override not honoured by virtual NICs
I have a SAN Network defined in oVirt where I have enabled Jumbo frames
(by setting the MTU to 9000).
Still I see now VM Nic;s attached to this network get MTU 1500 and are
therefore basically not working.
I have created several VMs before all (still) have Jumbo Frames on the
their san-interface, but newly created VMs get 1500.
Currently on 3.4 Beta2 (upgraded from alpha --> beta1 --->) and this
behaviour have started somewhere along the way..
The host physical interface
em2 Link encap:Ethernet HWaddr D0:67:E5:F9:2E:1C
inet6 addr: fe80::d267:e5ff:fef9:2e1c/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:9000 Metric:1
RX packets:503209263 errors:0 dropped:0 overruns:0 frame:0
TX packets:483040537 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2395173035170 (2.1 TiB) TX bytes:408352341106
(380.3 GiB)
And on a VM
vnet25 Link encap:Ethernet HWaddr FE:1A:4A:2F:D2:A3
inet6 addr: fe80::fc1a:4aff:fe2f:d2a8/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:167 errors:0 dropped:0 overruns:0 frame:0
TX packets:137 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:500
RX bytes:17662 (17.2 KiB) TX bytes:26684 (26.0 KiB)
If manully setting the MTU everything work as expected.. (Until you
reboot the machine)
Anyone else seen this ?
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.
The current method to control guest network internals is by using the
cloud-init-integration
however MTU is not part of its api [1].
You can add it to the 3.5 planning thread as a requested item.
[1] http://www.ovirt.org/Features/Cloud-Init_Integration
Rgds Jonas
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