Keyword: IPv4, IPv6, RIP, RIPng
Abstract: RIPng was developed from RIP to support IPv6. This document describes the RIPng implementation, differences between RIPng and RIP, and RIPng application scenarios.
Classless Inter-domain Routing
Interior Gateway Protocol
Routing Information Protocol
RIP next generation
Route Table Entry
Variable Length Subnet Mask
Table of Contents
RIP is a distance-vector Interior Gateway Protocol (IGP) developed by the IETF. It is widely used in small-sized IPv4 networks due to ease of implementation, configuration and maintenance.
RIPng works basically the same way as RIP but has some differences from RIP to support IPv6 address format. The following describes RIP briefly before detailing how different RIPng and RIP are.
RIP uses UDP and port 520 to exchange route information.
RIP uses a hop count to measure the distance to a destination. The hop count is known as a metric. The hop count from a router to a directly connected network is 0. The hop count from a router to a directly connected router is 1. To limit convergence time, a RIP metric ranges from 0 to 15. A metric value of 16 (or greater) is considered infinite, which means the destination network is unreachable.
The following describes how RIP works:
(1) After RIP is enabled, a router sends request messages to neighboring routers, and listens for RIP request or response messages from neighboring routers.
(2) Upon receiving response messages, the router processes the routing update information in the messages, updates its local routing table, and sends triggered update messages to its neighbors.
(3) All routers on the network do the same to keep the latest routing information.
By default, a RIP router sends its routing table to neighbors every 30 seconds. RIP ages out routes by adopting an aging mechanism to keep only valid routes.
RIP has two versions: RIPv1 and RIPv2.
RIPv1, a classful routing protocol, supports message advertisement via broadcast only. RIPv1 protocol messages do not carry mask information, which means it can only recognize routing information of natural networks such as Classes A, B, and C. That is why RIPv1 does not support discontiguous subnets.
RIPv2 is a classless routing protocol. Compared with RIPv1, RIPv2 has the following advantages:
l Supporting route tags. Route tags are used in route policies to flexibly control routes.
l Supporting masks, route summarization and Classless Inter-Domain Routing (CIDR).
l Allowing for designating the best next hop on a broadcast network.
l Supporting multicast routing update to reduce resource consumption.
l Supporting plain text authentication and MD5 authentication by adding an authentication route table entry (RTE) into updates to enhance security.
RIPng works basically the same way as RIP but has the following differences from RIP to support IPv6:
1. Different IP address lengths
RIPng uses 128-bit IP addresses, compared with RIPv2's 32-bit addresses.
2. Different packet lengths
A RIPv2 message carries up to 25 route entries, while the maximum number of RTEs in a RIPng packet depends on the IPv6 MTU of the sending interface.
3. Different packet formats
Like a RIPv2 packet, a RIPng packet consists of a header and multiple RTEs. The following figure shows the packet formats of RIP and RIPng:
Different from RIPv2, RIPng has two types of RTEs:
l Next hop RTE: Defines the IPv6 address of a next hop.
l IPv6 prefix RTE: A next hop RTE can be followed by multiple IPv6 prefix RTEs that use the same next hop. An IPv6 prefix RTE describes the destination IPv6 address, route tag, prefix length and metric of a RIPng route entry.
The following figure shows the format of the next hop RTE. IPv6 next hop address is the IPv6 address of the next hop.
The following figure shows the format of the IPv6 prefix RTE:
l IPv6 prefix: Destination IPv6 address prefix
l Route tag: Route tag
l Prefix length: Length of the IPv6 address prefix
l Metric: Cost of the route
4. Different packet sending modes
RIPv2 can be configured to periodically broadcast or multicast routing information, while RIPng periodically multicasts routing information.
In RIPng, the authentication RTEs have been removed. RIPng relies on the authentication mechanism of IPv6 to ensure integrity and validity.
l A school builds an IPv6 network. All routers and hosts in the network running IPv6.
l The school requires a small office network where any two nodes can communicate with each other and the network devices can automatically adapt to topology changes.
l RFC 2080: RIPng for IPv6
l RFC 2081: RIPng Protocol Applicability Statement
l RFC 1058: Routing Information Protocol
l RFC 1721: RIP Version 2 Protocol Analysis
l RFC 2082: RIP-2 MD5 Authentication
l RFC 2453: RIP Version 2
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