MPLS Label Distribution Protocol, LDP – Part 2

label-distribution-and-traffic-flow

Label Distribution

After LDP session establishment, labels are distributed from the Tail-End router to the Head-End router for each prefix. This process occurs at the opposite direction of the data plane. At the data plane the traffic flow goes form the Head-End to the Tail-End. But label distribution process is done at the opposite direction.

Label Distribution And Traffic Flow
 

Label Distribution And Traffic Flow
With these distribution, LIB and the LFIB tables are filled.

FIB, LIB, LFIB

These terms are very important terms in MPLS, We had also talked about this terms before, in the MPLS articles. But to recall, I would like to tell you again below.Lets begin with how this tables are filled.

All the routes to all the destinations are in RIB (Routing Information Base). The best routes to the destinations are choosed and stored in the Routing Table. Then the values in the Routing Table, are copied to the FIB(Forwarding Information Base). Labels for all the destinations are stored in the LIB (Label Information Base). And LFIB(Label Forwarding Information Base) table is filled with the best routes’s label values.

Below you can see the summary of these tables’s job and you can also see how to reach this tables on Alcatel-Lucent service routers.

RIB (Routing Information Base) : All routes to the all destinations

Routing Table : Best routes to the destination

A:># show route route-table

FIB (Forwarding Information Base) : Copy of routing table.

A:># show router fib 1

MPLS Label Distribution Protocol, LDP – Part 1
MPLS Label Distribution Protocol, LDP – Part 2
MPLS Label Distribution Protocol, LDP – Part 3 (Configuration on ALU)
MPLS Label Distribution Protocol, LDP – Part 4 (ECMP)
MPLS Label Distribution Protocol, LDP – Part 5 (Export and Import Policy, Prefix Aggregation)
MPLS Label Distribution Protocol, LDP – Part 6 (T-LDP)
MPLS Label Distribution Protocol, LDP – Part 7 (CR-LDP)

For more information about LDP, T-LDP and CR-LDP, check the related following RFCs...
RFC 5036: LDP Specification
RFC 3815: Definitions of Managed Objects for the MPLS,LDP
RFC 3478: Graceful Restart Mechanism for Label Distribution Protocol
RFC 5443: LDP IGP Synchronization
RFC 7307: LDP Extensions for Multi-Topology
RFC 7361: LDP Extensions for Optimized MAC Address Withdrawal in a H-VPLS
RFC 3212: Constraint-Based LSP Setup using LDP
RFC 3213: Applicability Statement for CR-LDP 
RFC 3214: LSP Modification Using CR-LDP

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