Numerous IPv4 routing protocols (RPs) are available for finding routes between networks, and almost every one of them has an IPv6 correspondent or extension: Routing Information Protocol next-generation (RIPng), Open Shortest Path First version 3 (OSPFv3), Intermediate System-to-Intermediate System (IS-IS), Enhanced Interior Gateway Routing Protocol (EIGRP), and Border Gateway Protocol (BGP). So far, IPv6 has brought few innovations to the IP routing paradigm. There are still interior gateway protocols (IGPs) and exterior gateway protocols (EGPs), distance vectorbased and link-state-based routing protocol algorithms, and so on.
The concept of the autonomous system, defined as a set of networks controlled by a common administrative entity, remains unchanged with the introduction of IPv6 RPs. The same autonomous system (and autonomous system number [ASN]) will route both IPv4 and IPv6. IPv6 IGPs, used to exchange routes within the autonomous system, are namely RIPng, OSPFv3, IS-IS for IPv6, and EIGRP for IPv6. Only BGP4 is available to exchange IPv6 routes between autonomous systems. Multiprotocol extensions provide support in BGP4 for IPv6 routing.
The requirements for IGPs and EGPs are quite different, in terms of routing table size, number of supported routers, convergence time, security, routing policy, and so forth. For that reason, they use different algorithms and mechanisms, which also affect the type of information they exchange and store. IGPs use distance vector and link state, whereas BGP uses the path vector RP algorithm. The following table represents RP taxonomy, and highlights their IPv6 correspondent. For more details on how to choose the RP, refer to Top-Down Network Design, Second Edition, by Priscilla Oppenheimer.
| Deployment Domain | Algorithm | RP | Scalability | Convergence Time | Metric | IPv6 Version |
|---|---|---|---|---|---|---|
| Interior gateway protocol (IGP) | Distance vector | RIP | 15 hops | Slow | Hop count | RIPng |
| EIGRP | 1000s routers | Quick (via DUAL algorithm) | Bandwidth, delay, reliability, load | EIGRP for IPv6 | ||
| Link state | OSPF | 1000s routers (100s/area) | Quick (via LSAs and HELLO) | Cost (function of bandwidth on Cisco routers) | OSPFv3 | |
| IS-IS | 1000s routers (100s/area) | Quick (via LSPs) | Configured host, delay, expense | IS-IS for IPv6 | ||
| Exterior gateway protocol (EGP) | Distance vector | EGP | Integer <=255 | |||
| Path vector | BGP AF=IPv4 | 1000s routers | Slow (via UPDATE) | Function of path attributes and other configurable factors | BGP AF=IPv6 |
The rest of this section briefly reviews existing unicast RP technologies. The next section reviews each of the available IPv6 RPs and provides configuration examples. Then the last two sections cover the topic of multihoming and deployment aspects, respectively.
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