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@redhat.com> To: "Devin Acosta" <devin@pabstatencio.com> Cc: "users" <Users@ovirt.org>, "Lance Richardson" <lrichard@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@pabstatencio.com> To: "Marcin Mirecki" <mmirecki@redhat.com>, "users" <Users@ovirt.org>, "Lance Richardson" <lrichard@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@pabstatencio.com> Date: Fri, Dec 9, 2016 at 2:02 PM Subject: oVirt / OVN / MTU To: users <Users@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?
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Devin Acosta Red Hat Certified Architect, LinuxStack 602-354-1220 || devin@linuxguru.co
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Devin Acosta Red Hat Certified Architect, LinuxStack 602-354-1220 || devin@linuxguru.co