3. Extended NLRI Encodings

In order to carry the Path Identifier in an UPDATE message, the NLRI encoding MUST be extended by prepending the Path Identifier field, which is of four octets.

For example, the NLRI encoding specified in [RFC4271] is extended as the following:

+--------------------------------+
| Path Identifier (4 octets)     |
+--------------------------------+
| Length (1 octet)               |
+--------------------------------+
| Prefix (variable)              |
+--------------------------------+

The usage of the extended NLRI encodings is specified in Section 5.