R3303-HP HSR6800 Routers MPLS Configuration Guide

• Incoming Label Map—ILM maps each incoming label to a set of NHLFEs. It is used to forward

labeled packets. When an LSR receives a labeled packet, it looks for the corresponding ILM entry.

If the Token value of the ILM entry is not null, the LSR looks for the corresponding NHLFE entry to

determine the label operation to be performed.

FTN and ILM are associated with NHLFE through Token.

MPLS data forwarding

Figure 7 MPLS forwarding process diagram

In an MPLS domain, a packet is forwarded in the following procedure:

1. Router B (the ingress LSR) receives a packet carrying no label. It determines the FEC of the packet

according to the destination address, and searches the FIB table for the Token value. Because the

Token value is not Invalid, Router B looks for the corresponding NHLFE entry that contains the

Token value. According to the NHLFE entry, Router B pushes label 40 to the packet, and forwards

the labeled packet to the next hop LSR (Router C) through the outgoing interface (GigabitEthernet

1/0/2).

2. Upon receiving the labeled packet, Router C looks for the ILM entry that contains the label 40 to

get the Token value. Because the Token value is not blank, Router C looks for the NHLFE entry

containing the Token value. According to the NHLFE entry, Router C swaps the original label with

label 50, and then forwards the labeled packet to the next hop LSR (Router D) through the outgoing

interface (GigabitEthernet 1/0/2).

3. Upon receiving the labeled packet, Router D (the egress) looks for the ILM entry according to the

label (50) to get the Token value. Because the Token is blank, Router D removes the label from the

packet. If the ILM entry records the outgoing interface, Router D forwards the packet through the

outgoing interface. If no outgoing interface is recorded, router D forwards the packet according to

the IP header of the packet.

PHP

In an MPLS network, when an egress node receives a labeled packet, it looks up the LFIB, pops the label

of the packet, and then performs the next level label forwarding or performs IP forwarding. The egress