11-21-2010 08:49 PM - edited 03-06-2019 02:09 PM
bgp is redistributed under ospf as below. i am trying to catch the meaning of route-map & its statements which is used here.
router ospf 5
redistribute bgp 1234 subnets route-map redistribute_bgp-to-ospf
route-map redistribute_bgp-to-ospf
route-map redistribute_bgp-to-ospf, deny, sequence 10
Match clauses:
tag 41
Set clauses:
Policy routing matches: 0 packets, 0 bytes
route-map redistribute_bgp-to-ospf, permit, sequence 20
Match clauses:
Set clauses:
tag 41
Policy routing matches: 0 packets, 0 bytes
Please help me to understand what does the tag 41 refer to and what does this entire statements do.I am unable to locate this tag in the configuration.
TIA
11-21-2010 09:35 PM
This route map is using the tag to avoid redistributing routes which have already been redistributed (which would contribute to a routing loop). The first instance in the route map says that if a route has a tag with value 41 then it should be denied redistribution. The second instance in the route map redistributes routes and assigns the redistributed route a tag with value of 41.
You will not find these tags anywhere else in the configuration. The tags are only used within the route map.
HTH
Rick
11-24-2010 03:04 AM
Thanks,
But how does the route-map know which routes are carrying tag 41 , so that it does the action of deny / permit as in the configurations.
TIA
11-24-2010 04:12 AM
Hi,
In BGP routes are tagged with most recent AS number but when redistributing into OSPF the tag is maintained.
So the first sequence of your route-map will not redistribute the routes having the tag 41 so announced by AS 41 and the second sequence will tag all the other BGP routes when redistributing them into OSPF. Are you multihomed? If not then you won't have any routes into OSPF if next hop is AS 41 and if you are then you will redistribute only routes from one ISP only.
Can someone confirm my reasoning is right?
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