# BookRiff

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## What is intra area in OSPF?

Intra Area routes are the “O” routes that you see in the routing table. These routes are routes that are in the same area. Inter-area routes are the “O IA” routes that are learned in different areas.

What does OSPF use to calculate the best route?

OSPF uses a cost metric that represents the status of the link and the bandwidth of the interface in an algorithm to determine the best route to a destination. The algorithm used is called the SPF (shortest path first) or Dijkstra algorithm.

Is OSPF inter or intra?

Both Intra and Inter-Area routes are also called OSPF Internal routes, as they are generated by OSPF itself, when an interface is covered with the OSPF network command. A Type-1 route is always preferred over a Type-2 route for the same destination.

### What is a NSSA area?

NSSA (Not so stubby area) is an OSPF area type that allows the injection of external routes into the stub area by using a special LSA type called LSA type 7. This LSA type 7 is converted into an LSA type 5 when it leaves the NSSA area.

How OSPF will calculate the metrics for external routes?

OSPF External E1 vs E2

• R2 will calculate the metric or cost between R2 and R3 and add to the seed cost advertised by R3. Hence, in this case, E1 cost for R2 shall be = Cost from R2 to R3 + Seed cost = 1 + 20 = 21.
• R2 will calculate the metric or cost to reach network 10.1.
• For E1 Route cost = 1+1+20 = 22.

What is OSPF cost preferred?

Routes with the better metric are preferred. Open Shortest Path First (OSPF) uses cost as the metric calculated, based on the bandwidth of the link. The cost of a link is calculated by dividing the reference bandwidth (100 Mbps by default) by the interface bandwidth.

#### What is the ad value of OSPF?

By default, OSPF has a default administrative distance of 110 and RIP has a default administrative distance of 120. Administrative distance values can, however, usually be adjusted manually by a network administrator.

How are intra area routes affected in OSPF?

Because OSPF is link state, there is no chance to use a concept like an offset-list to selectively modify the cost of a few of intra area routes: link state database must be identical in all routers that belong to the same area, so any change to the cost between routers would impact all routes.

How are routes redistributed in the OSPF model?

Hi Nguyenvancan110, Routes are redistributed in OSPF as either type 1 (E1) routes or type 2 (E2) routes, with type 2 being the default. A type 1 route has a metric that is the sum of the internal OSPF cost and the external redistributed cost. A type 2 route has a metric equal only to the redistributed cost.

## Which is the Order of preference for OSPF?

The order of preference for OSPF as per RFC 2328 is : intra-area routes, O interarea routes, O IA external routes type 1, O E1 external routes type 2, O E2 This rule of preference cannot be changed. I hope this helps.

How to set the default cost in OSPF?

To explicitly specify the cost of sending a packet on an interface, use the ip ospf cost command in interface configuration mode. To reset the path cost to the default value, use the no form of this command. ip ospf cost cost. no ip ospf cost Syntax Description Defaults No default cost is predefined.