H3C Technologies H3C SR8800 - Manual (Page 294)

278
Configuring RIPng
Introduction to RIPng
RIP next generation (RIPng) is an extension of RIP-2 for IPv4. Most RIP concepts are applicable in RIPng.
RIPng for IPv6 has the following basic differences from RIP:
• UDP port number—RIPng uses UDP port 521 for sending and receiving routing information.
• Multicast address—RIPng uses FF02:9 as the link-local-router multicast address.
• Destination Prefix—128-bit destination address prefix.
• Next hop—128-bit IPv6 address.
• Source address—RIPng uses FE80::/10 as the link-local source address.
RIPng working mechanism
RIPng is a routing protocol based on the distance vector (D-V) algorithm. RIPng uses UDP packets to
exchange routing information through port 521.
RIPng uses a hop count to measure the distance to a destination. The hop count is the metric or cost. The
hop count from a router to a directly connected network is 0. The hop count between two directly
connected routers is 1. When the hop count is greater than or equal to 16, the destination network or host
is unreachable.
By default, the routing update is sent every 30 seconds. If the router receives no routing updates from a
neighbor within 180 seconds, the routes learned from the neighbor are considered unreachable. If no
routing update is received within another 240 seconds, the router removes these routes from the routing
table.
RIPng supports split horizon and poison reverse to prevent routing loops and route redistribution.
Each RIPng router maintains a routing database, which includes route entries of all reachable
destinations. A route entry contains the following information:
• Destination address—IPv6 address of a host or a network.
• Next hop address—IPv6 address of a neighbor along the path to the destination.
• Egress interface—Outbound interface that forwards IPv6 packets.
• Metric—Cost from the local router to the destination.
• Route time—Time that elapsed since a route entry is last changed. Each time a route entry is
modified, the routing time is set to 0.
• Route tag—Identifies the route, used in a routing policy to control routing information. For more
information about routing policy, see the chapter “Configuring routing policies.”
RIPng packet format
Basic format
A RIPng packet consists of a header and multiple route table entries (RTEs). The maximum number of RTEs
in a packet depends on the IPv6 MTU of the sending interface.