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4. Dissemination of IPv4 Flow Specification Information

4. Dissemination of IPv4 Flow Specification Information​

This document defines a Flow Specification NLRI type that may include several components, such as destination prefix, source prefix, protocol, ports, and others (see Section 4.2 below).

This NLRI information is encoded using MP_REACH_NLRI and MP_UNREACH_NLRI attributes, as defined in [RFC4760]. When advertising Flow Specifications, the Length of the Next-Hop Network Address MUST be set to 0. The Network Address of the Next-Hop field MUST be ignored.

The NLRI field of the MP_REACH_NLRI and MP_UNREACH_NLRI is encoded as one or more 2-tuples of the form <length, NLRI value>. It consists of a 1- or 2-octet length field followed by a variable-length NLRI value. The length is expressed in octets.

                 +-------------------------------+
                 |    length (0xnn or 0xfnnn)    |
                 +-------------------------------+
                 |    NLRI value   (variable)    |
                 +-------------------------------+

             Figure 1: Flow Specification NLRI for IPv4

Implementations wishing to exchange Flow Specification MUST use BGP's Capability Advertisement facility to exchange the Multiprotocol Extension Capability Code (Code 1), as defined in [RFC4760]. The (AFI, SAFI) pair carried in the Multiprotocol Extension Capability MUST be (AFI=1, SAFI=133) for IPv4 Flow Specification and (AFI=1, SAFI=134) for VPNv4 Flow Specification.

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