Em 22 de nov de 2017 3:53 PM, "Aaron Gould" <aaron1@gvtc.com> escreveu: This is a *single area* ospf environment, that has been stable for years.. But now suddenly is having issues with new ospf neightbor adjacencies , which are riding a 3rd party transport network Anyone ever experienced anything strange with underlying transport network mtu possibly causing ospf neighbor adjacency to be broken ? Yes, the neighbor state will loop between init/Exchange and it will never become Full. As others said, you need to test the MTU size without fragmentation and adjust in your L3 interface (ping with DF-bit). I'm asking if the underlying 3rd party transport layer 2 network has a smaller mtu than the endpoint ospf ip interface have, could this cause those ospf neighbors to not fully establish ? IMHO, Your transport network must support your Full 1500 bytes MTU. No one want to deal with fragmentation. They need to activate jumbo frames to sell L2 circuits. .and I'm also asking this if the single ospf area has grown large enough to cause some sort of initial database packet to be larger than that underlying 3rd party mtu is providing Its normal to have a LSADB bigger than MTU could support, and with correct MTU this is not a problem. Regards, Rafael