[c-nsp] Bizarre MPLS label problem, hex value?

[Nathan]

On Feb 18, 2008 1:33 PM, Oliver Boehmer (oboehmer) <oboehmer at cisco.com> wrote:
>
> >> Please do "show ip cef ${D loopback}" on A to find out.
> >
> > A#show ip cef ${D loopback}
...
> >     tag rewrite with Gi0/1.7, ${B as seen from A}, tags imposed: {}
> >
> > Am I correct in supposing that there should be a tag imposed there?
>
> Yes, there should.
...
> > Could this possibly be some kind of redistribution problem between BGP
> > and OSPF? I redistribute some internal routes between BGP and OSPF,
> > but the why and the "how to avoid" of that is a story in itself.
>
> Oh. So is D's loopback seen via BGP, not via OSPF? as LDP doesn't assign
> or advertise any labels to BGP prefixes, you end up without a tag on D.

Could have been, but no, all loopbacks seem OK in OSPF. The thing I'm
not sure about is my redistributing some internal IPs from BGP into
OSPF, so I don't think that's the problem unless somehow the bgp
version replaces the ospf version, which is not the case: on all
routers when I do sh ip route ${D loopback} or ${A loopback} I have
"Known via ospf".

But OK, so this is an LDP problem between A and B, right? Now that I
look at it better, there is a problem with the ldp adjacency between A
and B.  Somehow I missed that B binds to no neighbor at all on the
interface that faces towards A (it should bind to A, Z, and three
others. A does bind to them). I launched debugging, and the problem
seems to be that B receives no LDP hellos at all on this interface. It
sends them, and they are seen, but on A I get (timestamped in the same
millisecond):

ldp: Rcvd ldp hello; GigabitEthernet0/1.7, from ${B as seen from A}
(${B loopback}:0), intf_id 0, opt 0xC
ldp: ldp Hello from ${B as seen from A} (${B loopback}:0) to 224.0.0.2, opt 0xC
ldp: local idb = GigabitEthernet0/1.7, holdtime = 15000, peer ${B as
seen from A} holdtime = 15000
ldp: Link intvl min cnt = 6, intvl = 5000, idb = GigabitEthernet0/1.7

All other logs look like the first line above, sending and receiving
hellos for adjacencies that are OK.

I can see nothing different in the configs (not that I trust myself
after having missed the missing LDP adj), and I'm reasonably certain
it has worked at some time in the past.

For now I'll change OSPF costs so nothing goes through there (not
trivial unfortunately since it's a very central link) and program a
reboot of B.

Thanks,
-- 
Nathan