Re: Strange behavior in a VRF switch with redistribution

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:
> 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
> <copley.chris_at_gmail.com>wrote:
>
>
>> 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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Received on Thu Apr 01 2010 - 00:33:57 ART