[ovirt-users] oVirt / OVN / MTU

[Lance Richardson]

Hi Devin,

This blog posting does a good job of explaining how to configure OVN
DHCP support:

    http://blog.spinhirne.com/2016/09/an-introduction-to-ovn-routing.html

The ovn-nb man page lists the DHCP options that can be provided, including
mtu:

    http://openvswitch.org/support/dist-docs/ovn-nb.5.html

And the ovn-nbctl man page has details about the command-line interface
for setting DHCP options:

    http://openvswitch.org/support/dist-docs/ovn-nbctl.8.html

I have very little experience using OVN's DHCP support, I've copied Numan
in case I've left anything out.

    Lance
----- Original Message -----
> From: "Marcin Mirecki" <mmirecki at redhat.com>
> To: "Devin Acosta" <devin at pabstatencio.com>
> Cc: "users" <Users at ovirt.org>, "Lance Richardson" <lrichard at redhat.com>
> Sent: Monday, December 12, 2016 4:35:51 AM
> Subject: Re: oVirt / OVN / MTU
> 
> 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
> > 
>