[c-nsp] MPLS "Tag Control" process - what does this do?

[Oliver Boehmer (oboehmer)]

Reuben Farrelly <> wrote on Friday, August 03, 2007 2:18 PM:

> Hi Rodney,
> 
>>> Aug  3 04:42:37.479: %TIB-3-REMOTETAG: 150.82.0.0/255.255.0.0, peer
>>> 61.84.96.254:0; tag 53643; Failure with LDP Label Release; prefix
>>> not in TIB Aug  3 04:43:08.171: %TIB-3-REMOTETAG:
>>> 192.232.71.0/255.255.255.0, peer 
>>> 61.84.96.254:0; tag 54898; Failure with LDP Label Release; prefix
>>> not in TIB 
[...]
> I've also just noticed that the 3550 behind this router and another
> one connected to that via an ethernet link to that switch also is
> pretty sick, and both nearly ran out of memory today.  Both have
> logged a lot of messages about "Aug  3 11:51:39: %FIB-2-FIBDOWN: CEF
> has been disabled due to a low memory condition. It can be re-enabled
> by configuring "ip cef [distributed]" 
> 
> 'show ip cef' on these switches shows that CEF is now not running. 
> My thinking is that this is a rather big problem in itself (!) and
> will try get these switches reloaded later tonight.
> 
> The reason I am bringing this up is that I'm considering if the
> problem may not have been directly caused by this 7200, but may be
> caused by some other external factor.  The only thing which strikes
> me as a possibility is that someone or something
> flooded/redistributed an entire BGP feed into OSPF.  Does that sound
> like a possibility? 

It actually sounds like a likely cause. Both of the prefixes LDP
complained about above (150.82.0.0/16 and 192.232.71.0/24) are Internet
prefixes (from different ASN, so likely not yours), so the only reason
LDP would be concerned about them was if they were advertised by an IGP
at some point of time (as we don't assign labels to BGP prefixes). 

As "Tag Control" is the main dispatching process for all sorts of MPLS
events, I could imagine that the router was pretty busy allocating (and
later de-allocating) labels :-|
 
	oli