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3. Multiprotocol Unreachable NLRI - MP_UNREACH_NLRI (Type Code 15)

3. Multiprotocol Unreachable NLRI - MP_UNREACH_NLRI (Type Code 15)​

This is an optional non-transitive attribute that can be used for the purpose of withdrawing multiple unfeasible routes from service.

The attribute is encoded as shown below:

+---------------------------------------------------------+
| Address Family Identifier (2 octets)                    |
+---------------------------------------------------------+
| Subsequent Address Family Identifier (1 octet)          |
+---------------------------------------------------------+
| Withdrawn Routes (variable)                             |
+---------------------------------------------------------+

The use and meaning of these fields are as follows:

Address Family Identifier:

This field carries the identity of the Network Layer protocol associated with NLRI being withdrawn. Presently defined values for this field are specified in RFC 1700 (see the Address Family Numbers section).

Subsequent Address Family Identifier:

This field provides additional information about the type of the Network Layer Reachability Information carried in the attribute.

Withdrawn Routes:

A variable length field that lists NLRI for the routes that are being withdrawn from service. The format depends on the Address Family Identifier and the Subsequent Address Family Identifier. When the Subsequent Address Family Identifier field is set to one of the values defined in this document, each NLRI is encoded as specified in RFC 1771 (BGP-4).

An UPDATE message that contains the MP_UNREACH_NLRI is not required to carry any other path attributes.

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