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3.5.10. Label Withdraw Message

An LSR sends a Label Withdraw Message to an LDP peer to signal the peer that the peer may not continue to use specific FEC-label mappings the LSR had previously advertised. This breaks the mapping between the FECs and the labels.

The encoding for the Label Withdraw 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|   Label Withdraw (0x0402)   |      Message Length           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Message ID                                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     FEC TLV                                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Label TLV (optional)                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Optional Parameters                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

FEC TLV Identifies the FEC for which the FEC-label mapping is being withdrawn.

Optional Parameters This variable length field contains 0 or more parameters, each encoded as a TLV. The optional parameters are:

  Optional Parameter    Length       Value

  Label TLV             variable     See below

The encoding for Label TLVs are found in Section "Label TLVs".

Label If present, specifies the label being withdrawn (see procedures below).

3.5.10.1. Label Withdraw Message Procedures​

An LSR transmits a Label Withdraw message under the following conditions:

  1. The LSR no longer recognizes a previously known FEC for which it has advertised a label.

  2. The LSR has decided unilaterally (e.g., via configuration) to no longer label switch a FEC (or FECs) with the label mapping being withdrawn.

The FEC TLV specifies the FEC for which labels are to be withdrawn. If no Label TLV follows the FEC, all labels associated with the FEC are to be withdrawn; otherwise, only the label specified in the optional Label TLV is to be withdrawn.

The FEC TLV may contain the Wildcard FEC Element; if so, it may contain no other FEC Elements. In this case, if the Label Withdraw message contains an optional Label TLV, then the label is to be withdrawn from all FECs to which it is bound. If there is not an optional Label TLV in the Label Withdraw message, then the sending LSR is withdrawing all label mappings previously advertised to the receiving LSR.

An LSR that receives a Label Withdraw message MUST respond with a Label Release message.

See Appendix A, "LDP Label Distribution Procedures", for more details.