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3.5.4. KeepAlive Message

An LSR sends KeepAlive messages as part of a mechanism that monitors the integrity of the LDP session transport connection.

The encoding for the KeepAlive message is:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|   KeepAlive (0x0201)        |      Message Length           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Message ID                                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Optional Parameters                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Message ID 32-bit value used to identify this message.

Optional Parameters No optional parameters are defined for the KeepAlive message.

3.5.4.1. KeepAlive Message Procedures​

The KeepAlive Timer mechanism described in Section "Maintaining LDP Sessions" resets a session KeepAlive Timer every time an LDP PDU is received on the session TCP connection. The KeepAlive message is provided to allow reset of the KeepAlive Timer in circumstances where an LSR has no other information to communicate to an LDP peer.

An LSR MUST arrange that its peer receive an LDP message from it at least every KeepAlive Time period. Any LDP protocol message will do

but, in circumstances where no other LDP protocol messages have been sent within the period, a KeepAlive message MUST be sent.