Label Distribution Protocol
Page 224 7210 SAS M, T, X, R6, Mxp MPLS Configu-
ration Guide
Execution Flow
LDP activity is limited to service-related signaling. Therefore, the configurable parameters are
restricted to system-wide parameters, such as hello and keepalive timeouts.
Initialization
MPLS must be enabled when LDP is initialized. LDP makes sure that the various prerequisites,
such as ensuring the system IP interface is operational, the label manager is operational, and there
is memory available, are met. It then allocates itself a pool of memory and initializes its databases.
Session Lifetime
In order for a targeted LDP (T-LDP) session to be established, an adjacency must be created. The
LDP extended discovery mechanism requires hello messages to be exchanged between two peers
for session establishment. After the adjacency establishment, session setup is attempted.
Session Establishment
When the LDP adjacency is established, the session setup follows as per the LDP specification.
Initialization and keepalive messages complete the session setup, followed by address messages to
exchange all interface IP addresses. Periodic keepalives or other session messages maintain the
session liveliness.
Since TCP is back-pressured by the receiver, it is necessary to be able to push that back-pressure
all the way into the protocol. Packets that cannot be sent are buffered on the session object and re-
attempted as the back-pressure eases.
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