Hello All, I would like to learn more about OVN and especially the maximum MTU that I can use in my environment. Current Setup 4.3.10 Network was created via UI -> MTU Custom -> 8976 -> Create on External Provider -> Connect to Physical Network So my physical connection is MTU 9000 and I have read that Geneve uses 24 bits (maybe that's wrong ?) , thus I have reduced the MTU to 8976.

I did some testing on the VMs and ping with payload of '8914' was the maximum I could pass without fragmenting and thus the MTU on the VMs was set to 8942. Did I correctly configure the test network's MTU and am I understanding it correctly that we need extra 34 bits inside the network for encapsulation ? I have checked https://www.ovirt.org/develop/release-management/features/network/managed... but I don't see any refference how to calculate the max MTU. Best Regards, Strahil Nikolov _______________________________________________ Users mailing list -- users(a)ovirt.org To unsubscribe send an email to users-leave(a)ovirt.org Privacy Statement: https://www.ovirt.org/privacy-policy.html oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ List Archives: https://lists.ovirt.org/archives/list/users@ovirt.org/message/CKNS5T5KE2W...

On Tue, Oct 27, 2020, 02:49 Strahil Nikolov via Users <users(a)ovirt.org&gt; wrote: > Hello All, > > I would like to learn more about OVN and especially the maximum MTU that I can use in my environment. > > Current Setup 4.3.10 > Network was created via UI -> MTU Custom -> 8976 -> Create on External Provider -> Connect to Physical Network > > So my physical connection is MTU 9000 and I have read that Geneve uses 24 bits (maybe that's wrong ?) , thus I have reduced the MTU to 8976. From the internet draft it seems that the tunnel header + reserved bits comprise 64 bits. A common practice for Geneve implementations  is to use 8900 mtu for VMs when having 9000 mtu physical network.

The draft: https://tools.ietf.org/html/draft-ietf-nvo3-geneve-08 >   > I did some testing on the VMs and ping with payload of '8914' was the maximum I could pass without fragmenting and thus the MTU on the VMs was set to 8942. > > Did I correctly configure the test network's MTU and am I understanding it correctly that we need extra 34 bits inside the network for encapsulation ? >

>  I have checked https://www.ovirt.org/develop/release-management/features/network... but I don't see any refference how to calculate the max MTU. > > > Best Regards, > Strahil Nikolov > _______________________________________________ > Users mailing list -- users(a)ovirt.org > To unsubscribe send an email to users-leave(a)ovirt.org > Privacy Statement: https://www.ovirt.org/privacy-policy.html > oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ > List Archives: https://lists.ovirt.org/archives/list/users@ovirt.org/message/CKNS5T5KE2W... > >   _______________________________________________ Users mailing list -- users(a)ovirt.org To unsubscribe send an email to users-leave(a)ovirt.org Privacy Statement: https://www.ovirt.org/privacy-policy.html oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ List Archives: https://lists.ovirt.org/archives/list/users@ovirt.org/message/VIDP3MLYHWG...

in 4.3.10's UI it shows 1500 :)

If you mean "Administration" -> "Providers" -> "Ovirt-provider-ovn" -> it is enabled.

Best Regards, Strahil Nikolov В петък, 30 октомври 2020 г., 21:10:02 Гринуич+2, Strahil Nikolov < hunter86_bg(a)yahoo.com&gt; написа: Any hint for the location of "Automatic Synchronization" in UI ? Best Regards, Strahil Nikolov В петък, 30 октомври 2020 г., 20:16:13 Гринуич+2, Dominik Holler < dholler(a)redhat.com&gt; написа: On Fri, Oct 30, 2020 at 7:03 PM Strahil Nikolov <hunter86_bg(a)yahoo.com&gt; wrote: > in 4.3.10's UI it shows 1500 :) > This might be just a misleading representation of the default value or an unknown value. If "Automatic Synchronization" is enabled for the ovirt-provider-ovn in oVirt Engine, the value should be updated in Engine to the correct after the next synchronization in the background. > > > > > > В петък, 30 октомври 2020 г., 13:25:05 Гринуич+2, Dominik Holler < dholler(a)redhat.com&gt; написа: > > > > > > > > On Thu, Oct 29, 2020 at 9:36 PM Alex K <rightkicktech(a)gmail.com&gt; wrote: >> >> >> On Tue, Oct 27, 2020, 02:49 Strahil Nikolov via Users <users(a)ovirt.org&gt; wrote: >>> Hello All, >>> >>> I would like to learn more about OVN and especially the maximum MTU that I can use in my environment. >>> >>> Current Setup 4.3.10 >>> Network was created via UI -> MTU Custom -> 8976 -> Create on External Provider -> Connect to Physical Network >>> >>> So my physical connection is MTU 9000 and I have read that Geneve uses 24 bits (maybe that's wrong ?) , thus I have reduced the MTU to 8976. >> From the internet draft it seems that the tunnel header + reserved bits comprise 64 bits. A common practice for Geneve implementations is to use 8900 mtu for VMs when having 9000 mtu physical network. >> > > Ack, this is a safe choice. > In oVirt's default configuration, an overhead of 58 bytes > ( = 20 IPv4 header + 8 UDP header + 16 GENEVE Ethernet header (including 8 bytes options) + 14 bytes inner Ethernet header) > is added. > This is why the default MTU for OVN networks in oVirt is 1442 bytes, which assumes 1500 bytes MTU in the physical network. > > > >> >> The draft: >> https://tools.ietf.org/html/draft-ietf-nvo3-geneve-08 >>> >>> I did some testing on the VMs and ping with payload of '8914' was the maximum I could pass without fragmenting and thus the MTU on the VMs was set to 8942. >>> >>> Did I correctly configure the test network's MTU and am I understanding it correctly that we need extra 34 bits inside the network for encapsulation ? >>> > > You could check with packet analyzers like tcpdump and wireshark. > >>> I have checked https://www.ovirt.org/develop/release-management/features/network/managed... but I don't see any refference how to calculate the max MTU. >>> >>> >>> Best Regards, >>> Strahil Nikolov >>> _______________________________________________ >>> Users mailing list -- users(a)ovirt.org >>> To unsubscribe send an email to users-leave(a)ovirt.org >>> Privacy Statement: https://www.ovirt.org/privacy-policy.html >>> oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ >>> List Archives: https://lists.ovirt.org/archives/list/users@ovirt.org/message/CKNS5T5KE2W... >>> >>> >> _______________________________________________ >> Users mailing list -- users(a)ovirt.org >> To unsubscribe send an email to users-leave(a)ovirt.org >> Privacy Statement: https://www.ovirt.org/privacy-policy.html >> oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ >> List Archives: >> https://lists.ovirt.org/archives/list/users@ovirt.org/message/VIDP3MLYHWG... >> >> > _______________________________________________ > Users mailing list -- users(a)ovirt.org > To unsubscribe send an email to users-leave(a)ovirt.org > Privacy Statement: https://www.ovirt.org/privacy-policy.html > oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ > List Archives: > https://lists.ovirt.org/archives/list/users@ovirt.org/message/7UN5DXXKXN3... > >