Did some OSPF labbing yesterday. Ran into some interesting
stuff. Imagine that you are running a frame-relay network which
is hub and spoke. All routers are using their main interface for
communication. The hub router has the static frame relay mapping
with the broadcast keyword but the spokes don’t. They are all
running OSPF network type point-to-multipoint. What will happen
if we only have broadcast capability in one direction? The hub
router sends multicast out its main interface reaching all the
spokes. The surprising part is that spokes reply with unicast
packet using immediate hello. The adjacency forms and everything
is fine and dandy. However after a while the hub declares the
spokes as dead, why? Since the spokes don’t have multicast
capability the hub never receives their hello packets. Remember
the hello packets are used as keepalive mechanism so after 120
seconds they are declared dead. Quite an interesting scenario
and would be interesting to put as trouble ticket at the CCIE
lab If you as I neve