OSPF Basics Flashcards
What is an AS ?
An AS consists of a collection of networks under a common administration that share a common routing strategy. An AS, which is sometimes called a domain, can be logically subdivided into multiple areas.
What is an Area ?
An area is a grouping of contiguous networks. Areas are logical subdivisions of the AS.
Within an AS, what area must be defined ?
Backbone Area (Area 0) . Non area backbones are connected to the backbone area.
How are called routers in the backbone area ?
Backbone routers
How are called routers in non-backbone areas ?
Internal routeurs
What is an ABR (Area border router) ?
A router that connects Area 0 to non backbones Areas
Which information ABRs contains ?
LSDB information for each area
What is an ASBR router ?
AS boundary router. It’s a router that has at least one of its interface connected to an OSPF area and at least one of its interface connected to an external non-OSPF domain.
What is the general recommandation regarding the number of routers per area ?
No more than 50 routers per area.
In a single OSPF area, what happens when there is a change in topology ?
- New LSAs are created and sent throughout the area.
- All routers change their LSDB when they receive the LSA.
- SPF algorithm is run again on the updated LSDB to verify new paths destination within the area.
What does the OSPF dynamic protocol do ?
- Create Neighbor relationship by exchanging Hello Packets
- Propagate LSAs instead of routing table updates. LSA are composed of Link (router interface) and State (description of an interface and its relationship to neighboring routers)
- Flood LSAs to all OSPF routers in the area
- Pieces together all the LSAs that OSPF routers generate to create the OSPF LSDB
- Uses the SPF algorithm to calculate the shortest path to each destination and places it in the routing table
How often a router sends LSAs ?
Immediatly if there is a change in topology or every 30 minutes.
