[c-nsp] ldp: label not assigned for eBGP-learned route..

[Harold Ritter (hritter)]

Alexander,

This behavior is normally seen when ipv4 + label is not configured on
the iBGP peer(s). Can you confirm whether send-label is configured for
the iBGP peer and do a "show bgp ipv4 unicast neighbor x.x.x.x" for the
iBGP peer to confirm that ipv4 + label is both advertised and received.

Regards, 

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Alexandre
Snarskii
Sent: Saturday, June 09, 2007 11:07 AM
To: Cisco-NSP Mailing List
Subject: [c-nsp] ldp: label not assigned for eBGP-learned route..


Hi!

While testing interAS mpls connectivity, I found interesting
feature: router does not assign local label to route, learned via eBGP,
even in case when got it with label...

A bit more detailed description: 
I'm getting route with label, 

BGP routing table entry for AA.AAA.AA.5/32, version 5022
    BB.BBB.B.49 from BB.BBB.B.49 (BB.BBB.B.6)
      Origin IGP, metric 0, localpref 100, valid, external, best
      Community: no-export
      mpls labels in/out nolabel/101824

and it's installed into mpls forwarding table with outgoing label: 

Router>show mpls forwarding-table AA.AAA.AA.5
Local  Outgoing      Prefix            Bytes Label   Outgoing   Next Hop

Label  Label or VC   or Tunnel Id      Switched      interface

None   101824        AA.AAA.AA.5/32    0             Vl99
BB.BBB.B.49 

But, as you can see, Local Label is not assigned to this route, so, even
if that route redistributed with iBGP over my backbone, label for this
route is not assigned at the edge, so, all other routers will not be
able to establish LSP to remote side... 

Well, one workaround to this is to redistribute this route to ospf (this
route get label assigned right after enabling bgp->ospf redistribution),
but that workaround is potentially dangerous[1].

Are there any way to force local label assignment to eBGP-learned route
without redistribution ? 

PS: IOS version is 12.2(33)SRA3, if it matters. 

[1]: Some years ago I saw a network meltdown caused by 'no redistribute
bgp NNNN route-map BLAH', which removed not 'redistribute' command, but
just 'route-map', thus allowing full-view leak into ospf.. With modern
IOS behaviour (disable dCEF when there are not enough memory) such leaks
are even more dangerous...

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