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To avoid “infinite count”, RIPng provides mechanism such as “split horizon” and “triggered
update” to solve route loop. “Split horizon” is done by avoiding sending to a gateway routes
leaned from that gateway. There are two split horizon methods: “simple split horizon” and
“poison reverse split horizon”. Simple split horizon deletes from the route to be sent to the
neighbor gateways the routes learnt from the neighbor gateways; poison reverse split horizon
not only deletes the abovementioned routes, but set the costs of those routes to infinite.
“Triggering update” mechanism defines whenever route metric changed by the gateway, the
gateway advertise the update packets immediately other than wait for the 30 sec timer.
So far the RIPng protocol has got only one version----Version1: RIPng protocol is introduced
in RFC 2080. RIPng transmits updating data packet by multicast data packet (multicast address
FF02::9)
Each layer3 switch running RIPng has a route database, which contains all route entries for
reachable destination, and route table is built based on this database. When a RIPng layer3
switch sent route update packets to its neighbor devices, the complete route table is included in
the packets. Therefore, in a large network, routing data to be transferred and processed for each
layer3 switch is quite large, causing degraded network performance.
Besides the above mentioned, RIPng protocol allows IPv6 route information discovered by
the other routing protocols to be introduced to the route table.
The operation of RIPng protocol is shown below:
Enable RIPng The switch sends request packets to the neighbor layer3 switches by
broadcasting; on receiving the request, the neighbor devices reply with the packets containing
their local routing information.
The Layer3 switch modifies its local route table on receiving the reply packets and sends
triggered update packets to the neighbor devices to advertise route update information. On
receiving the triggered update packet, the neighbor lay3 switches send triggered update packets
to their neighbor lay3 switches. After a sequence of triggered update packet broadcast, all layer3
switches get and maintain the latest route information.
In addition, RIPng layer3 switches will advertise its local route table to their neighbor devices
every 30 seconds. On receiving the packets, neighbor devices maintain their local route table,
select the best route and advertise the updated information to their own neighbor devices, so
that the updated routes are globally valid. Moreover, RIP uses a timeout mechanism for outdated
route, that is, if a switch does not receive regular update packets from a neighbor within a certain
interval (invalid timer interval), it considers the route from that neighbor invalid, after holding the
route fro a certain interval (garbage collect timer interval), it will delete that route.
As a result of continuous development of IPv6 network, it has the network environment of
nonsupport IPv6 sometimes, so it needs to do the IPv6 operation by tunnel. Therefore, our
RIPng supports configuration on configure tunnel, and passes through nonsupport IPv6 network
by unicast packet of IPv4 encapsulation.