OSPF Theory Flashcards
What is OSPF?
Open Shortest Path First - a non-proprietary link-state routing protocol
What is an LSA?
Link State Advertisement - information about an individual routers links aka networks.
What is an ABR?
Area Border Router - a router that has interfaces on networks that are in different OSPF areas.
What is an ASBR?
Autonomous System Border Router - a router that is running OSPF and also redistributing non-OSPF routes.
Describe a Type 1 LSA
Router Link - lists the router’s neighboring routers and the cost to each; flooded within an area.
Describe a Type 2 LSA
Network Link - Only sent by the DR. Lists all routers on an adjacent segment; flooded within an area.
Describe a Type 3 LSA
Network Summary (OSPFv3: Inter-Area Prefix)- only sent by the ABR. Advertises network prefixes that originated from another OSPF area.
Describe a Type 4 LSA
ASBR Summary (OSPFv3: Inter-Area Router) - Sent by ABR into the backbone. Advertises the presence of an ASBR within an area.
Describe a Type 5 LSA
External Link - Generated by ASBR and flooded throughout the area to advertise a route that is External to OSPF.
Describe a Type 7 LSA
NSSA External Link - Sent by ASBR in a Not-So-Stubby-Area; Converted to a type 5 LSA by the ABR when it leaves the area.
Describe a Type 8 LSA
OSPFv3 Link - IPv6 only. These are for IPv6 Intra-Area link local addresses.
Describe a Type 9 LSA
IPv6 Network Link - IPv6 prefix advertisements that are only flooded within that area.
When do routers exchange their entire Link State DB with each other?
When those neighbors are fully adjacent.
What is effectively happening when you issue the ‘network’ command within OSPF config mode?
You are telling the router to enable all interfaces within the specified network range for OSPF and to advertise their networks.
What is a stub network?
A network where this is only one router. In other words, there are no other networks beyond that network.
What is a stub area?
An OSPF area that does not accept redistributed routes from an ASBR.
What is the formula for the number of neighbor adjacencies formed in an OSPF broadcast segment?
Where N is the number of OSPF routers: N(N-1)/2
What is a DR in OSPF?
Designated Router - The router that is responsible for advertising route updates. Only the DR forms full OSPF adjacencies with the other routers in the segment.
How is a DR elected in a network segment?
1.) First to come online
2.) Highest OSPF priority
3.) Highest Router ID (RID)
- Highest IP on Loopback
- Highest IP on Non-loopback
What is the BDR?
Backup Designated Router - takes over if the DR goes offline