OSPF

[ghimeko1]

can i know what is the point of LS sequence when there's also LS age?

[MHM Cisco World · Accepted solution]

How router detect Out of order of update with age?

It need seq to check out or order of update of ospf 

MHM

[ghimeko1]

wait, im srry i dont read it carefully

[ghimeko1]

so the TLDR would be like this?

• LS Sequence Number helps identify the latest version of an LSA.
• LS Age ensures that outdated LSAs are eventually purged, even if updates stop being received.

[Martin L]

Yes, if u need more details, there is good ospf info in the TCP/IP volume 1 book from Cisco press by J. Dolye. 

Regards, ML
**Please Rate All Helpful Responses **

[Martin L · Accepted solution]

RFC 2328:

If the LS age field of one of the router's self-originated LSAs reaches the value LSRefreshTime [30 minutes], a new instance of the LSA is originated, even though the contents of the LSA (apart from the LSA header) will be the same.

(...)

Whenever a new instance of an LSA is originated, its LS sequence number is incremented, its LS age is set to 0, its LS checksum is calculated, and the LSA is added to the link state database and flooded out the appropriate interfaces.

(...)

When comparing an LSA to its previous instance, the following are all considered to be differences in contents:

(...)

• The body of the LSA (i.e., anything outside the 20-byte LSA header) has changed. Note that this excludes changes in LS Sequence Number and LS Checksum.

Also  see OSPF section in https://www.cisco.com/c/en/us/tech/ip/ip-routing/tsd-technology-support-troubleshooting-technotes-list.html

 https://community.cisco.com/t5/switching/ospf-sequence-number-question/td-p/3220777

and search the CLN

Regards, ML
**Please Rate All Helpful Responses **