LSA Exclusion in OSPF Routing Calculation

[salmanrozik]

Hello, I have two questions and need clarification on some aspects of OSPF. I would greatly appreciate any help in this regard.

1 : Router XR in an OSPF network area receives an LSA concerning link L1 from router YR but excludes this information from its shortest path route calculations despite storing it in its database. Why does this exclusion occur, excluding 'link cost' as a factor?

2: Designers of OSPF had choices regarding its placement in the protocol stack:

• Option 1: Above Layer 4 (transport layer) using TCP or UDP.
• Option 2: Directly above Layer 3 (IP layer).
• Option 3: Above Layer 2 (data link layer). Which option did they select and why? What are potential drawbacks of the other two options that were not chosen?

[MHM Cisco World]

If the link between two router then always router select it self originate lsa than one receive from neighbor and hence it use itself link cost 

For second Q can you more elaborate' there is no l4 for ospf 

MHM

[salmanrozik]

Q2: When designing the OSPF routing protocol, the designers had the
following choices regarding its placement within the protocol stack:
▪ Option 1: Place the OSPF protocol above the Layer 4 transport layer,
with OSPF packets transported over either TCP (Transmission Control
Protocol) or UDP (User Datagram Protocol) segments.
▪ Option 2: Place the OSPF protocol directly above the IP (Internet
Protocol) layer, where OSPF packets are transported over Layer 3 IP
datagrams.
▪ Option 3: Place the OSPF protocol directly above the data link layer, with
OSPF packets transported over Layer 2 data link layer frames.

[MHM Cisco World]

How you control ospf to make it above or down layer ?

The oapf is standard l3 protocol' yoh can not change that.

Do you read this in specific doc. Can I see it

MHM