Where a cisco-router writes a tag value when I use a 'set tag' command in a route-map? For example:

route-map TO_XXX permit 10
 match ip address TO_XXX
 set tag 99

Is it saved in IP-packet? In which field? How a next router gets this 99 for comparing with match tag?

1 Answer 1


The tags are advertised by the routing protocol, not in the IP packet. In both OSPF and EIGRP, there is a tag field in the route advertisements (LSA for OSPF, external TLV for EIGRP). So neighboring routers learn the tags as they learn the prefixes.


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