IPv6 Routing

Routing in IPv6 is almost identical to IPv4 routing under CIDR, except that 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 functionality. These capabilities include:

• 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 functionality by creating sequences of IPv6 addresses using 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 cases, to reverse routes in a packet it receives (if the packet was successfully authenticated using the IPv6 authentication header) containing address sequences in order to return the packet to its originator. This approach makes IPv6 host implementations support the handling and reversal of source routes. This is the key that allows them to work with hosts that implement the new features, such as provider selection or extended addresses.