From: kevin gannon (kevin@gannons.net)
Date: Wed Mar 04 2009 - 06:41:54 ARST
Roman
Thanks for this however I am still confused. I am only pushing the topic
as it is another way to ensure an end to end label when used with
next-hop-unchanged.
> Yes, if it's the last BGP session in a chain, then you'll need to
> redistribute routes into something. The reason for it is that LFIB will not
> populate until there's an "IN" label for the prefix created by the router.
> IOS won't create the IN label until it's either:
>
> 1. Redistributed into some IGP (it doesn't have to be a real IGP in use, a
> simple "router ospf 1" + "redistribute bgp X subnets" will do)
> 2. The prefix has to be forwarded on by BGP to another eBGP or iBGP
> send-label peer.
>
> If you do "show ip bgp labels" and you don't see an "In" label for the
> prefix, the prefix will not appear in the LFIB.
>
I took the previous example and added another router R20 attached it to R19.
Then I peered via iBGP between R19 and R20. This I think meet the second
requirement above. However the same results:
R19
==============================================
show ip bgp nei 100.100.100.20 adv
BGP table version is 3, local router ID is 100.100.100.19
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 100.100.100.16/32
189.189.189.8 0 17 16 i
*> 100.100.100.19/32
0.0.0.0 0 32768 i
show ip bgp 100.100.100.16
BGP routing table entry for 100.100.100.16/32, version 3
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Advertised to update-groups:
2
17 16
189.189.189.8 from 189.189.189.8 (100.100.100.18)
Origin IGP, localpref 100, valid, external, best,
mpls labels in/out nolabel/19
R20
===========================================
show ip bgp 100.100.100.16
BGP routing table entry for 100.100.100.16/32, version 2
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Not advertised to any peer
17 16
189.189.189.8 (metric 2) from 100.100.100.19 (100.100.100.19)
Origin IGP, metric 0, localpref 100, valid, internal, best,
mpls labels in/out nolabel/19
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