Showing posts from April, 2022

NSX-T T0 BGP routing considerations regarding MTU size

     Recently I had serious NSX-T production issue with BGP involved and T0 routing instance on edge VMs cluster, in terms of not having routes inside routing table on T0 - which supposed to be received from ToR L3 device. NSX-T environment has several options regarding connections from fabric to the outside world. These type of connections goes over T0 instance, which can be configured to use static or dynamic routing (BGP, OSPF) for this purpose. MTU is important consideration inside NSX environment, because of GENEVE encapsulation inside overlay (should be minimum 1600bytes - 9k ideally). Routing protocols are also subject to MTU check (OSPF is out of scope for this article, but you know that MTU is checked during neighborship establishment). Different networking vendors are using various options for MTU path discovery - by default this mechanisms inside BGP should be enabled (but of course should be checked and confirmed). Problem arrives when you configure ToR as ie 9k MTU capable