Label to FEC Binding

Unanswered Question
Jan 22nd, 2008
User Badges:
  • Bronze, 100 points or more

Hi All

I ve a doubt regarding who will do the Label to FEC bindnig.. Is it done by LDP or by FEC...

I m in an assumption that LDP (or any signalling prtocol in that matter) will only distribute the labels for the prefixes in the routing table to its neighbor and Global MPLS process does the Label to FEC binding.. But i ve read in some documents the Binding for Labels to FEC is done by LDP..

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
attrgautam Tue, 01/22/2008 - 08:38
User Badges:
  • Silver, 250 points or more

AFAIK and from my basic understanding of 3036, LDP is responsible for end-to-end creation of the LSP and this also includes the binding of the FEC to the label (in effect the LSP).

senthil_kumarpv Mon, 01/28/2008 - 05:00
User Badges:

As per the mpls architecture ,data plane and control plane architect mpls,the part which u mentioned is done by the control plane in the mpls



sultan-shaikh Mon, 01/28/2008 - 23:00
User Badges:
  • Bronze, 100 points or more


There is no relation between LDP and FEC as to how the binding occurs.

FEC as you might be knowing stands for Forwarding Equivalence Class which is nothing but a "group" of packets to be handled in a similar way, in most MPLS networks this is packets assigned to a particular destination or Destination based forwarding.

Once the routes are learnt by the routing table via an IGP, LDP will assign labels and create a binding between routes and label i.e. a label table showing which label is assigned to which route.

LDP also exchanges the labels between its Peers.


senthil_kumarpv Tue, 01/29/2008 - 01:25
User Badges:


"Labels are bound to the routes in the routing table "



arun kumar Sat, 02/02/2008 - 00:53
User Badges:
  • Bronze, 100 points or more

Labels are bound to the routes in the RIB or FIB.( FIB is a copy of RIB)

There wont be any FIB or Adjacency table when CEF is disabled.

Local label binding for the PREFIX is not happening when CEF is disabled.

According to you if the routes are taken from RIB ,there should be an local label binding for the prefix in the routing table(RIB). Mon, 02/04/2008 - 22:00
User Badges:

Hi Arun,

First would like to add here is that LDP is not used to assign labels to FEC. LDP's function is to distribute the labels locally generated as well as received from remote bindings.

CEF is used to assign labels.

Also, FIB is not a copy of RIB. FIB points to the outgoing interface and also the recursive lookup is already performed.

So, for your question "No" LDP is not used to assign labels.



Nikhil E.


This Discussion