Introduction to IPv6 IS-IS
The IS-IS routing protocol (Intermediate System-to-Intermediate System intra-domain routing information exchange protocol) supports multiple network protocols, including IPv6. The international engineer task force (IETF) defines two type-length-values (TLVs) and a new network layer protocol identifier (NLPID) to enable IS-IS to support IPv6.
TLV is a variable-length field in the link state PDU or link state packet (LSP). The TLVs include the following:
IPv6 Reachability—Defines the prefix, metric of routing information to indicate network reachability, and has a type value of 236 (0xEC).
IPv6 Interface Address—Same as the "IP Interface Address" TLV in IPv4 ISIS, except the 32-bit IPv4 address is translated to the 128-bit IPv6 address.
The NLPID is an eight-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 a router that supports IPv6 IS-IS.