Ldp Working Process - 3Com 3C13636 Configuration Manual

3Com Router 3000 Ethernet Family
Configuration Guide
II. LDP Session
An LDP session is to exchange label and release messages between LSRs. There are
two types of LDP session:
Local LDP Session: an LDP session between two directly connecting LSRs.
Remote LDP Session: an LDP session between two indirectly connecting LSRs.
III. LDP Message
There are four types of message involved in the LDP.
Discovery message: used to notify or maintain the existing LSRs in the network;
Session message: used to establish, maintain or terminate a session between
LDP peers;
Advertisement message: used to establish, modify or delete a flag, that is, an FEC
binding;
Notification message: used to provide suggestive messages or error notifications.
IV. Label Space and LDP Identifier
A label space refers to the range of labels that can be allocated to LDP peers. You can
specify a label space for each interface of an LSR or for the entire LSR.
An LDP identifier is to identify a special LSR label space. It is a six-byte value in the
following format:
<IP address> : <Label space number>
Here the IP address of four bytes is the LSR IP address and the remaining two bytes is
the label space number.

1.4.2 LDP Working Process

Figure 1-5 illustrates the LDP label distribution.
Ingress
LSP2
E
MPLS LER
Figure 1-5 Label distribution process
A
B
Label Request
Label Mapping
F
LDP Session
3Com Corporation
LSP1
Egress
C
G
H
1-7
Chapter 1 MPLS Architecture
D
MPLS LSR