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Operation Manual – MPLS Basics
H3C S9500 Series Routing Switches
Chapter 1 MPLS Basics Configuration
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Using LDP, LSRs can map network layer routing information to data layer switching
paths directly and further establish LSPs. LSPs can be established between both
neighboring LSRs and LSRs that are not directly connected, making label switching
possible at all transit nodes on the network.
Note:
For detailed description about LDP, refer to RFC 2036 “LDP Specification”.
I. LDP peer
Two LSRs with an LDP session established between them and using LDP to exchange
label to FEC bindings are called LDP peers, each of which obtains the label to FEC
bindings of its peer over the LDP session between them.
II. LDP session
LDP sessions are used to exchange messages for label binding and releasing.
LDP sessions come in two categories:
z
Local LDP session: Established between two directly connected LSRs.
z
Remote LDP session: Established between two indirectly connected LSRs.
III. LDP message type
There are four types of LDP messages:
z
Discovery message: Used to declare and maintain the presence of an LSR on a
network.
z
Session message: Used to establish, maintain, and terminate sessions between
LDP peers.
z
Advertisement message: Used to create, alter, or remove label to FEC bindings.
z
Notification message: Used to provide advisory information and signal errors.
For reliable transport of LDP messages, TCP is used for LDP session messages,
advertisement messages, and notification messages, while UDP is used only for
discovery messages.
IV. Label space and LDP identifier
A scope of labels that can be assigned to LDP peers is called a label space. A label
space can be per interface or per platform. A per interface label space is
interface-specific, while a per platform label space is for an entire LSR.