IPv6 (Intermediate System-to-Intermediate System) IS-IS provides all the features of IPv4 IS-IS. The difference between IPv6 IS-IS and IPv4 IS-IS is that IPv6 IS-IS advertises IPv6 routing information.
IS-IS supports multiple network layer protocols, including IPv6. IS-IS that supports IPv6 is referred to as IPv6 IS-IS. The RFC5308 specifies a method for exchanging IPv6 routing information using the IS-IS routing protocol. The described method utilizes two new Type-Length-Values (TLVs) and a new Network Layer Protocol Identifier (NLPID).
TLV is a variable-length field in a link state PDU or link state packet (LSP). The two new TLVs are:
IPv6 Reachability
The type is 236 (0xEC). It describes network reachability by defining the information such as route prefixes and metrics.
IPv6 Interface Address
The type is 232 (0xE8). It equals to TLV IP Interface Address in IPv4, except for the change from the original 32-bit IPv4 address to a 128-bit IPv6 address.
NLPID is an 8-bit field that identifies the network layer protocol. The value of the IPv6 NLPID is 142 (0x8E). If an IS-IS router supports IPv6, it must advertise the IPv6 routing information in the IPv6 NLPID TLV.