cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
928
Views
20
Helpful
4
Replies

OSPF Type 2 LSA

Ravi Pande
Beginner
Beginner

Hello,

I am studying about type2 Lsa in OSPF and many places have pseudonode mentioned. I am having hard time understanding about the pseudonode concept. Could anyone explain about this?
Also, second question, how does type2 Lsa help build the spf tree in OSPF?

Thanks in advance

4 Replies 4

Deepak Kumar
Advocate
Advocate

Hi,

What is type 2 LSA:

SLA Name: Network LSA

Generated by: DR router

Link-state ID: Interface IP of DR router.

Network SLAs are generated by the DR on the multi-access network. The segment that does not have DR such as point to point, will not have a network LSA. 

 

Regards,

Deepak Kumar

Regards,
Deepak Kumar,
Don't forget to vote and accept the solution if this comment will help you!

balaji.bandi
VIP Community Legend VIP Community Legend
VIP Community Legend

Type 2: network LSA -- For broadcast networks only; this LSA is flooded by the DR and lists OSPF-speaking routers on the network. 

 

spf tree in OSPF?

 

When the Link State database is synchronized within an area, the Dijkstra algorithm is run against it in two passes to form the shortest-path (SPF) tree. The first pass against the SPF database forms the branches, or router adjacencies within the area. The second pass adds all leaves or stub networks to the tree. When OSPF builds the tree, it determines the shortest path to each destination based on the sum cost to the destination. The lower the cost is, the more preferred the route is. The cost of a route is the sum of all costs of outgoing interfaces to that destination. Oddly enough, RFC 2328 offers no specific values for cost. Nortel Networks, for example, implements OSPF under RFC 2328 and uses the same formula to generate cost as Cisco Systems. In multivendor environments, take the extra time to see how cost is calculated because it will help OSPF have a consistent view of the entire internetwork.

Cisco routers calculate OSPF cost as (108/BW) rounded down, where BW is the configured or default bandwidth of the interface.

Cost will be changed based on the interface and speed.

BB

***** Rate All Helpful Responses *****

How to Ask The Cisco Community for Help

paul driver
VIP Expert VIP Expert
VIP Expert

Hello


@Ravi Pande wrote:

Hello,

I am studying about type2 Lsa in OSPF and many places have pseudonode mentioned. I am having hard time understanding about the pseudonode concept. Could anyone explain about this?


pseudonode =  think of it as a virtual router that the ospf physical routers interfaces in a broadcast/mulit-access network connect to.

 

 second question, how does type2 Lsa help build the spf tree in OSPF?

LSA type 2 ( network) are created from designated routers (DR) on multiaccess-links and lists all its routers connected to it (pseudonode ). The LSA is only advertised (flooded) in the area it was created.

This virtual router has no ospf cost associated with it and as such isn't included in any SPF calculation, Only the cost of the actual broadcast link of the routers interface is calculated meaning that two ospf neighbors on a broadcast/mulit-access link have their respective ospf cost calculated based on their ospf interface, so this virtual router (pseudonode) takes no part in any SPF process.


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul

Thanks for your reply.

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community:

Recognize Your Peers