MPLS basic#2 label exchange and LIB table

In front of the label exchange, by each of the LSR Address Message, and sends the information of the IP address of your interface.The reason has been described above .

To see this result in Cisco, use the following command.

# Show mpls ldp neighbor

Then, by each of the LSR Label Mapping Message, and then transfer label that you have assigned to locally (Local Label) to the LDP peer.

The label that was received by the Label Mapping Message is called the Remote Label.Based on this information, each LSR will constitute a LIB.

To see the LIB with Cisco, use the following command.

# Show mpls ldp bindings

FEC destination NW address and ToS value, or the like, or combinations thereof , but was above the, RFC3036 types of FEC are marked with (3.4.1. FEC TLV) is, Host and Prefix (destination NW address) only two types of Address.

In addition, as can be seen from the label area is a 20bit, labels that can be utilized [0 - 2 ^ 20] is, but the label number that can be used in the normal FEC in the LDP will be from 16.

0 - 15 are assigned as follows.

0: IPv4 Explicit Null Label
1: Router Alert Label
2: IPv6 Explicit Null Label
3: Implicit Null Label
4 - 15: Reserved

In R1 of the figure, the direct connection NW, Label 3 (Implicit Null Label) has been is used.This is a mechanism called PHP (Penultimate Hop Poppoing).Details will be discussed later.

As an example, take a look at the LIB of the R1.

FEC (Prefix)
LSR (LDP ID) Local 3 -
Remote 17
Remote 20 Local 22 -
Remote 20
Remote 22 Local 3 -
Remote 3
Remote 17 Local 3 -
Remote 18
Remote 3 Local 17 -
Remote 3
Remote 3 Local 18 -
Remote 3
Remote 18 Local 3 -
Remote 16
Remote 19 Local 16 -
Remote 3
Remote 16 Local 19 -
Remote 22
Remote 3 Local 21 -
Remote 19
Remote 21