IPv6 Routing

Routing in IPv6 is almost identical to IPv4 routing under CIDR. The only difference is the addresses are 128-bit IPv6 addresses instead of 32-bit IPv4 addresses. With very straightforward extensions, all of IPv4's routing algorithms (such as OSPF, RIP, IDRP, IS-IS) can be used to route IPv6.

IPv6 also includes simple routing extensions that support powerful new routing capabilities. The following list describes the new routing capabilities:

• Provider selection (based on policy, performance, cost, and so on)

• Host mobility (route to current location)

• Auto-readdressing (route to new address)

You obtain the new routing capability by creating sequences of IPv6 addresses that use the IPv6 routing option. An IPv6 source uses the routing option to list one or more intermediate nodes (or topological group) to be visited on the way to a packet's destination. This function is very similar in function to IPv4's loose source and record route option.

In order to make address sequences a general function, IPv6 hosts are required, in most instances, to reverse routes in a packet that a host receives. The packet must be successfully authenticated by using the IPv6 authentication header. The packet must contain address sequences in order to return the packet to its originator. This technique forces IPv6 host implementations to support the handling and reversal of source routes. The handling and reversal of source routes is the key that enables providers to work with hosts that implement the new features. The new features include provider selection and extended addresses.