OSPF Notes

• OSPF cannot make adjacencies over secondary addresses.
• OSPF routes of secondary addresses must be in same area as the primary address to be advertised.
• There can be more than 1 DR per OSPF area, there is only 1 DR per broadcast segment.
• OSPF does NOT support unnumbered point-to-point links.
• Distribute-list IN prevents the OSPF routes from being installed in the routing table [they still come into the OSPF database].
• To stop routers from becoming OSPF neighbors on a particular interface, configure the passive-interface command ON the interface.
• The only time that OSPF will form adjacencies between neighbors that are not on the same subnet is when the neighbors are connected through point-to-point links.
• Always configure a loopback interface before configuring OSPF.
• IP OSPF NAME-LOOKUP to configure the DNS name.
• In OSPF, there is a route selection rule that an intra-area route is prefered over an IA route. This is prefered over an external route.
• Use NO PEER NEIGHBOR if using PPP. This will prevent the DC [demand circuit] from flapping [up/down] and this will also suppress the /32 routes.