[ovirt-users] oVirt / OVN / MTU

[Marcin Mirecki]

Devin,

oVirt does not currently support changing external network mtu from within ovirt (it rather relies on the provider handling this internally).

If you are using OVN DHCP (have subnets defined for a network), you can modify the OVN DHCP options directly in the OVN database.
I have never actually tested this myself, but looking at the OVN documentation, it should do the job on the ports.

The standard OVN way to do so is to use the "ovn-vsctl set DHCP_Options ..." command.
(Unfortunately as I am trying it now it tells me that modifying DHCP_Options is not supported)
Alternatively, you can use the OVS python API (let me know if you need any help on this).

Lance,
Would changing the dhcp:options:mtu suffice?
Could you please comment on how to modify the DHCP MTU using the OVN cmd line?

Thanks,
Marcin



----- Original Message -----
> From: "Devin Acosta" <devin at pabstatencio.com>
> To: "Marcin Mirecki" <mmirecki at redhat.com>, "users" <Users at ovirt.org>, "Lance Richardson" <lrichard at redhat.com>
> Sent: Monday, December 12, 2016 1:20:59 AM
> Subject: Fwd: oVirt / OVN / MTU
> 
> Marcin / Lance,
> 
> Not sure if the list was working correctly, I couldn't see that my message
> below made it to the list. If I need to change the MTU settings for OVN /
> OpenVSwitch to something lower than 1500, what is the best way to do this?
> We noticed that some instances (ie: Windows 2012R2) are having issues with
> the default MTU of 1500, I think there is an issue at the upper layers, and
> we can get it to work if we manually set the MTU on the instance to say
> 1400. Is there an easy way to do this so that any VM's that come up
> automatically get MTU of 1400?
> 
> Devin
> 
> ---------- Forwarded message ----------
> From: Devin Acosta <devin at pabstatencio.com>
> Date: Fri, Dec 9, 2016 at 2:02 PM
> Subject: oVirt / OVN / MTU
> To: users <Users at ovirt.org>
> 
> 
> 
> We are running oVirt 4.0.5 and we have OVN working to provide a Virtual
> Layer 2 network. We are noticing that because the OVN is using Geneve and
> between all the firewalls and networks it crosses we are running into an
> MTU issue. What is the best suggested way to lower say the entire OVN
> network to say MTU of 1400, and also allow for fragmenting packets?
> 
> 
> --
> 
> Devin Acosta
> Red Hat Certified Architect, LinuxStack
> 602-354-1220 || devin at linuxguru.co
> 
> 
> 
> --
> 
> Devin Acosta
> Red Hat Certified Architect, LinuxStack
> 602-354-1220 || devin at linuxguru.co
>