4. ADD-PATH Capability

The ADD-PATH Capability is a BGP capability [RFC5492], with Capability Code 69. The Capability Length field of this capability is variable. The Capability Value field consists of one or more of the following tuples:

+------------------------------------------------+
| Address Family Identifier (2 octets)           |
+------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+------------------------------------------------+
| Send/Receive (1 octet)                         |
+------------------------------------------------+

The meaning and use of the fields are as follows:

Address Family Identifier (AFI): This field is the same as the one used in [RFC4760].

Subsequent Address Family Identifier (SAFI): This field is the same as the one used in [RFC4760].

Send/Receive: This field indicates whether the sender is (a) able to receive multiple paths from its peer (value 1), (b) able to send multiple paths to its peer (value 2), or (c) both (value 3) for the <AFI, SAFI>.

If any other value is received, then the capability SHOULD be treated as not understood and ignored [RFC5492].

A BGP speaker that wishes to indicate support for multiple AFI/SAFIs MUST do so by including the information in a single instance of the ADD-PATH Capability.