Strange behavior in a VRF switch with redistribution
Experts,
I am seeing a strange behavior and it has me purplexed. I have a 6500 that I am running 2 VRF’s on (no mpls) to isolate a guest network. On this same switch I have BGP running to another site and mutual redist between OSPF and BGP. No where on the core am I setting any route tags to any routes, but when I look at the other side of the WAN circuit I am seeing routes come across with the BGP AS# for a route tag.
-D1-WS2#sho ip route 207.16.70.0 Routing entry for 207.16.70.0/24 Known via “ospf 1″, distance 110, metric 17 Tag 65534, type extern 1 Last update from 10.218.80.186 on TenGigabitEthernet1/1, 02:15:42 ago Routing Descriptor Blocks: * 10.218.80.186, from 10.173.0.194, 02:15:42 ago, via TenGigabitEthernet1/1 Route metric is 17, traffic share count is 1 Route tag 65534
And if I look at the site with the VRF installed I see the info below
D1-CS1#sho ip route 207.16.70.0 Routing entry for 207.16.70.0/24 Known via “bgp 65002″, distance 120, metric 27 Tag 65001, type external Redistributing via ospf 1 Advertised by ospf 1 subnets Last update from 1.1.1.1 3d06h ago Routing Descriptor Blocks: * 1.1.1.1, from 1.1.1.1, 3d06h ago Route metric is 27, traffic share count is 1 AS Hops 1 Route tag 65001 MPLS label: none
I can only guess this is happening b/c of the VRF’s on the 6500. On the 6500 I can also see it has a place for the MPLS label (guess it is b/c of the VRF’s also? Can any one confirm this type of behavior?
Thanks Christopher
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Christopher,
Yes, the tag gets set from the AS number. See RFC 1403 for some interesting history. I don’t know if it’s considered some sort of standard but I think it is the default on most recent Cisco routers, although I normally don’t see BGP redistributed into OSPF. You can always set the tag to 0 with a route-map.
On Wed, Mar 31, 2010 at 2:22 PM, Christopher Copley wrote:
I believe this is a loop prevention mechanism, PE routers will ignore type 5 LSAs if the route tag matches the local BGP AS No. Type 3 LSAs use the down bit for loop (feedback) prevention, but Type 5 LSAs don’t support the down bit.
John Brooker
Bryan Bartik wrote:
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