Overview
Intermediate System-to-Intermediate System (IS-IS) supports multiple network protocols, including IPv6. To support IPv6, the IETF added two type-length-values (TLVs) and a new network layer protocol identifier (NLPID).
The TLVs are as follows:
IPv6 Reachability—Contains routing prefix and metric information to describe network reachability and has a type value of 236 (0xEC).
IPv6 Interface Address—Same as the "IP Interface Address" TLV in IPv4 ISIS, except that the 32-bit IPv4 address is translated to the 128-bit IPv6 address.
The new NLPID is an 8-bit field that identifies which network layer protocol is supported. For IPv6, the NLPID is 142 (0x8E), which must be carried in hello packets sent by IPv6 IS-IS.