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OSPF: Router-LSA

Hi,

How Router-LSAs are transmitted all through the area.Consider in the following diag:

R1---R2---R3, where R1 has point-to-point connection with R2, and R2 has point-to-point connection with R3.

In this case, how Router-LSA of R1 reaches R3.

Thanks,

Vijay

1 ACCEPTED SOLUTION

Accepted Solutions
Purple

Re: OSPF: Router-LSA

Hi Vijay,

It seems as if you are confused between the concepts of Link State Updates and Link State Advertisements. LSAs contain discrete pieces of link information - these are not packets by themselves. When an OSPF router conducts flooding, it includes one or more LSAs within an LS Update packet. Check out RFC2328 section A.3.5 for what a LS update packet looks like. In a nutshell, the LS Update encapsulates one or more LSAs within it.

Now, relating this to your question: when R2 receives R1's LSA, it will flood it to R2 within a LS update packet.

Hope that helps,

Paresh

6 REPLIES

Re: OSPF: Router-LSA

Hi,

R2 will send it with it´s source IP of the serial to 224.0.0.5 on the serial to R3 (assuming no DR is involved).

The content of this OSPF LS update (packet type 4) is the router LSA of R1. So it will contain the source router ID R1 and all the info R1 has to tell.

Hope this helps

Martin

New Member

Re: OSPF: Router-LSA

Hi,

I am not clear.What type of LSA is used by R2 to tranmit R1's Router-LSA ? I think it can't send as Router-LSA, since Router-LSA's are self originated describing its own links.Could you pls clear me on this.

Thanks,

Vijay

Purple

Re: OSPF: Router-LSA

Hi Vijay,

It seems as if you are confused between the concepts of Link State Updates and Link State Advertisements. LSAs contain discrete pieces of link information - these are not packets by themselves. When an OSPF router conducts flooding, it includes one or more LSAs within an LS Update packet. Check out RFC2328 section A.3.5 for what a LS update packet looks like. In a nutshell, the LS Update encapsulates one or more LSAs within it.

Now, relating this to your question: when R2 receives R1's LSA, it will flood it to R2 within a LS update packet.

Hope that helps,

Paresh

New Member

Re: OSPF: Router-LSA

Hi,

In that case, R2 packs self-orginated Router-LSA and also R1's Router-LSA in the LS Update packet.Then,why is it mentioned that'LSAs are send just one hop further' ? Correct me if I am wrong.

Thanks,

Vijay

Re: OSPF: Router-LSA

Hi,

LS update packets are just sent one hop. The content (LSA) is examined and sent further on in case it is new information.

So LSAs are flooded throughout an area within LS packets hop by hop.

Hope this helps

Martin

New Member

Re: OSPF: Router-LSA

Hi,

Thanks for all your reply.

Vijay

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