OSPF Type-5 AS External Link States

[srimal99]

Hi All, 

Currently trying to decrypt what  is the reason behind Tags  and what tag depicts in the

show ip ospf database[

Type-5 AS External Link States

Link ID             ADV Router       Age          Seq#       Checksum           Tag

172.16.0.113    10.0.0.113      631         0x80000001 0x00F006         0

172.16.0.118    10.0.0.114      678         0x80000001 0x009775         0

[MHM Cisco World · Accepted solution]

do small lab 
R1-R2 -R3
R1-R2 between run BGP 
in R2-R3 between run OSPF 
when redistribute BGP into OSPF the tag is automatic add to LSA5 as AS number of BGP, 
this tag can use for 
filter 
prevent routing loop 

[David Ruess · Accepted solution]

Hello,

Route tags are usually added to routes with redistribution or injecting routes into a domain to….well, tag routes. The purpose of that is to be able to filter or match groups of routes based on a tag they were assigned. So if I redistribute routes from EIGRP to OSPF I can tag those routs with a number. Then later in the topology I can set up a filter to say “all routes with this tag do this thing” whatever it is I have them do. It could be to drop, it could be more redistribution. At the end of the day it’s a value assigned to routes to match for route manipulation.

Hope that help

-David