OSPF Flashcards
What is the Administrative distance for OSPF?
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Administrative distance is used in determining what route gets installed in the routing table when the route is learned from multiple sources.
How are OSPF routers identified?
Router IDs are used to uniquely identify an OSPF router.
How long are router ids (In bits)
Router IDs are 32 bits long in both IPv4 and IPv3
How can we determine a wildcard mask?
To determine the wildcard mask, subtract the normal mask from 255.255.255.255
• A wildcard mask bit of 0 – match the bit
• A wildcard mask bit of 1 – ignore the bit
• A wildcard mask is a series of 0s with the rest 1s (the 0s and 1s are not alternating like an IP address)
What is ABR?
Area Border Router (ABR) – A router that has interfaces attached to multiple areas.
ABR connects area 0 with another area/s
What happens if a router-id is not configured?
The highest configured loopback interface is used. If not → highest active IPv4 address used (not recommended)
What does a passive interface do?
Passive interface do not send OSPF messages. Best practice for interfaces that have users attached (security)
What types of OSPF routers do we have?
Internal Router → Router that has all of its interfaces in the same Area
Backbone router → Router in the backbone area. (area 0)
Area Border Router → Router with interfaces attached to multiple areas
What is LSA?
The LSAs (Link-State Advertisements) are used by routers running OSPF to exchange topology information.
How are OSPF route calculations calculated?
- All routers calculate the best path or paths to destinations within their area
(intra-area). These are the type 1 and type 2 LSAs – O. - All routers calculate the best path or paths to the other areas within the
internetwork. Type 3 LSAs - O IA. - All routers calculate the best path or paths to the external autonomous system
(type 5) destinations - O E1 or an O E2
