MPLS questions

Unanswered Question
Jan 26th, 2009

I've got a couple of questions about MPLS:

What is the difference between LFIB and LIB? For some reason, I keep confusing these.



I have this problem too.
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Overall Rating: 5 (3 ratings)
Harold Ritter Mon, 01/26/2009 - 06:57


The LIB is maintained by LDP and contains the locally allocated and received labels. It is control plane only and is not used to forward traffic. The LFIB is used for MPLS forwarding as such (tag to tag or tag to IP operation). It is created from the FIB and LIB.


Jon Marshall Mon, 01/26/2009 - 07:00


The LIB (Label Information Base) is part of the control plane.

The LFIB (Label Forwarding Information Base) is part of the data plane.

The control plane is responsible for exchanging routes/labels with other routers/switches. In a non-MPLS router the equivalent of the LIB is the routing table.

The data plane is responsible for the actual forwarding of the packets. In a non-MPLS router the equivalent of the LFIB is the FIB (Forwarding Information Base).


lamav Mon, 01/26/2009 - 09:52

Jon, all the answers were good, but I like the way you juxtaposed an MPLS device with non-MPLS. It made everything crytstal clear.

I rated.

Mohamed Sobair Mon, 01/26/2009 - 09:07


Label Information base, is a table contains Label bindings associated with Prefixes. a Label Switch router Performs Lookup On the LIB table to forward (IP to IP) or (IP 2 Label). Every Label Switch router has distribute label bindings to its neighbor LSR using different modes could be either:

1- Per Interface Label allocation: This is the case for LC-ATM Interfaces (Downstream On demand) Cell Mode. In this case, a Label Switch router distribute Label binding Only if it receive a request from the Downstream LSR.

2- Per Platform Label allocation: This is case for Frame-mode Mpls (Unsolicited Down strem) In this case, a label Switch router distribute Label binding to every Label Switch router.

All of the Above is part of the Control Plane.To view LIB table, issue the command (Sh Mpls Ldp Binding).

Label Forward Information Base (LFIB):-

This is Part of the Data Plane, a LSR performs Lookup at the LFIB to forward (Label 2 label) or (Label 2 IP). The LFIP table Contains:

a- Incoming Label.

b- Outgoing Label.

c- Exit Interface.

d- Nexthop address.

to View the LFIB table, issue the command (sh Mpls forwarding-table).




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