Foundation Summary

MPLS is not a difficult subject to grasp conceptually. It amounts to essentially another routing process without all the overhead or useless information. It should be noted that said useless information is only useless to devices whose sole wish is to forward things regardless of what they contain. All that matters is label-in, FEC, and label-out.

MPLS essentially breaks into two components, as outlined in Table 9-2. Table 9-2 MPLS Planes



Control plane

Exchange routing information and labels

Data plane

Forward packets based on labels

Several tables are constructed in the MPLS architectures. Table 9-3 provides some review of those tables.

Table 9-3 MPLS Information Bases


Built By




IGP routing processes

Known destination prefixes, outbound interfaces, and next-hop addresses

Maps destination networks to next-hop address and outbound interface. Also forwards unlabeled packets.


LDP or other label distribution method

Local labels, FEC, LDP information

Associate local labels with FECs. Also performs label distribution to adjacent peers.


IGP and LDP information

Label-in, FEC, outinterface, label-out

Database used to forward labeled packets to next-hop addresses.

Adjacency table

Forming of neighbor relationship

Out-Interface and encapsulation along with neighbor ARP information

Maintain needed layer 2 information as well as LDP exchange capabilities.

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