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LSA 1 – Router LSA

Router LSA is generated by every router in the OSFP domain. This LSA contains all the information about the LINKS a router has. Since this router contains all the links information, this LSA is enough for making the OSPF database (Then why do we need other LSAs?).

A Router LSA describes a router and its links. So Number of Router LSA = Number of Routers in the area.

A router LSA will have below information :-
1. Connected links
2. Links Type – There are 4 types of links in OSPF
— P2P > This link is used to describe the P2P links such as serial links or manual configured P2P ethernet links
–Transit > This link is for transit networks and these links have Full adjacency with other OSPF speaking neighbor router.
–Loopback | Stub > This link is in OSPF domain but does not have any full adjacency with other OSPF neighbor. E.g. such as
Loopback interface.
–Virtual Link > This link is for giving information about the OSPF virtual links.

Router LSA Link Types with example

3. Metric – Router LSA also carries the link metric which is used for shortest path computation.
NOTE :: ROUTER LSA NEVER CROSSES AN AREA, THEY ARE LIMITED TO INTRA AREA ONLY AND USED BY SPF ALGORITHUM.
Now lets capture the router LSA in our LAB.

OSPF LAB USED FOR THE EXAMPLE – KEEP this Topology handy as it will be used in all LSA explanations

So we have enabled the OSPF between R1 and R2 and adjacency between R1 and R2 is Full.


Lets see if these two routers shared any LSA 1 or Router LSA


So as we can see above there are two Router LSA, one by R1 and one by R2. Lets examine the LSA 1 shared by R1 :-

Router LSA fields and their significance

So this was all about the LSA 1 and its field with detailed description. Drop a comment or contact us if you have any further queries.

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