I was trying to configure ospf router, I have a router connected to FW in G1/0/10 and mpls router connected g1/0/1, when i typed passive interface default in the ospf router i lost all connectivity and the neighbor between the mpls and core switch, so my question is this command take the internet down?
A passive interface in OSPF does not send hello packets, so it will never form a neighbor relationship nor exchange routes with another OSPF router.
By setting the
passive interface default command, you make all OSPF interfaces passive. The router will lose all its neighbors and with them, routing information.
It is often good practice to use the
passive interface default on devices, especially ones with lots of interfaces, then issue the
no passive interface command just for interfaces that actually have OSPF neighbors.
By setting an interface to passive, you will never form a neighbor on that interface. Unless you use the
no passive interface command on at least one interface, you will have no neighbors and get no routes from any other router. Basically, you could just disable OSPF and get the same result.
If you have many interfaces where there will be no neighbors, then the
passive interface default command is useful, but you then need to use the
no passive interface <interface> command for those interfaces where you do want neighbors.