3com DUA1750-2BAA01 Manual De Usuario

3Com Switch 8800 Configuration Guide 

Chapter 35  MPLS Architecture

 

35-4 

In independent control mode, each LSR can send label mapping messages to the 

LSRs it connects to at anytime. 

In ordered control mode, a LSR can send label mapping messages to upstream only 

when it receives a specific label mapping messages of the next hop of a FEC or the 

LSR serves as LSP (Label Switching Path) egress node. 

 

  Note: 

Currently, the Switch 8800 adopts the ordered label control mode. 

 

5) Label 

retention 

mode 

There are two label-retention modes: liberal label retention mode and conservative 

label retention mode. 

Suppose there are two LSRs: Ru and Rd. For a specific FEC, if LSR Ru has received 

the label binding from LSR Rd, in case Rd is not the next hop of Ru and Ru saves this 

binding, then it is the liberal label retention. And if Ru discards this binding, then it is the 

conservative label retention mode. 

In case it is required that LSR is capable of adapting route variation rapidly, you can use 

the liberal label retention mode. In case it is required that a few labels are saved in LSR, 

you can use the conservative label retention mode. 

 

  Note: 

Currently, the Switch 8800 adopts the liberal label retention mode. 

 

Label distribution protocol (LDP) is the signaling control protocol in MPLS, which 

controls binding labels and FECs between LSRs and coordinates a series of 

procedures between LSRs. 

The basic composing unit of MPLS network is LSR (Label Switching Router). It runs 

MPLS control protocol and L3 routing protocol, exchanges routing messages with other 

LSRs and create the routing table, maps FECs with IP packet headers, binds FECs