RIPng Cisco CCSP Coaching Institute in New Delhi

Network Bulls
www.networkbulls.com
Best Institute for CCNA CCNP CCSP CCIP CCIE Training in India
M-44, Old Dlf, Sector-14 Gurgaon, Haryana, India
Call: +91-9654672192

RIPng (RIP next generation) is the version of RIP that can be used in IPv6 networks. It is described in RFC 2080. Most of the RIP mechanisms from RIPv2 remain the same. RIPng still has a 15-hop limit, counting to infinity, and split horizon with poison reverse. A hop count of 16 still indicates an unreachable route.

Instead of using UDP port 520 as in RIPv2, RIPng uses UDP port 521. RIPng supports IPv6 addresses and prefixes. RIPng uses multicast group FF02::9 for RIPng updates to all RIPng routers.

RIPng Timers

RIPng timers are similar to RIPv2. Periodic updates are sent every 30 seconds. The default invalid timeout for routes to expire is 180 seconds, the default holddown timer is 180 seconds, and the default garbage-collection timer is 120 seconds.

Authentication

RIPng does not implement authentication methods in its protocol as RIPv2 does. RIPng relies on built-in IPv6 authentication functions.

RIPng Message Format

Figure 10-5 shows the RIPng routing message. Each route table entry (RTE) consists of the IPv6 prefix, route tag, prefix length, and metric.

The following describes each field:

• Command— Indicates whether the packet is a request or response message. This field is set to 1 for a request and to 2 for a response.
• Version— Set to 1, the first version of RIPng.
• IPv6 prefix— The destination 128-bit IPv6 prefix.
• Route tag— As with RIPv2, this is a method that distinguishes internal routes (learned by RIP) from external routes (learned by external protocols). Tagged during redistribution.
• Prefix length— Indicates the significant part of the prefix.
• Metric— This 8-bit field contains the router hop metric.

RIPv2 has a Next Hop field for each of its route entries. An RTE with a metric of 0xFF indicates the next-hop address to reduce the number of route entries in RIPng. It groups all RTEs after it to summarize all destinations to that particular next-hop address. Figure 10-6 shows the format of the special RTE indicating the next-hop entry.

RIPng Design

RIPng has low scalability. As with RIPv2, it is limited to 15 hops; therefore, the network diameter cannot exceed this limit. RIPng also broadcasts its routing table every 30 seconds, which causes network overhead. RIPng can be used only in small networks.

RIPng Summary

The characteristics of RIPng are as follows:

• Distance-vector protocol for IPv6 networks only.
• Uses UDP port 521.
• Metric is router hop count.
• Maximum hop count is 15; infinite (unreachable) routes have a metric of 16.
• Periodic route updates are sent every 30 seconds to multicast address FF02::9.
• Uses IPv6 functions for authentication.
• Implements split horizon with poison reverse.
• Implements triggered updates.
• Prefix length included in route entry.
• Administrative distance for RIPv2 is 120.
• Not scalable. Used in small networks.