Hi All, We have just finished building a new virtualised MT core network which is running very sweetly indeed. We have OSPF running in the core to handle redundancy between core routers, we will also run OSPF between core routers and edge routers as we do now, however in the new core we decided to use BFD to improve failover times should a problem occur. In the core network OSPF and BFD have been stable for some time, no problems, however we brought our first new site into the core last night and BFD just wouldn't come up on the link. The link comes in on a VLAN to the core, nothing fancy, just OSPF interface with BFD enabled, and OSPF Network definition. OSPF came up fine, just BFD wouldn't. BFD was still up on all other OSPF interfaces on the core router, however when we disabled BFD on the new interface to the site it took down OSPF on the entire router, same when you enable it on just that interface. We have checked MTU's and everything we can think of but BFD just won't come up on this link. We even upgraded ROS to latest bugfix on both ends of the link, no change. Firewall rules allowing OSPF protocol and BFD ports have been setup also. I'm just wondering if anybody has come across this issue before, firstly the BFD not working, but secondly the entire OSPF area going down on the router just by enabling or disabling BFD on one static OSPF interface. Thanks Paul