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224.0.0.9). Subnet mask field and RIP authentication filed (simple plaintext password and
MD5 password authentication are supported), and support variable length subnet mask.
RIP-II used some of the zero field of RIP-I and require no zero field verification. layer3
switches send RIP-II packets in multicast by default, both RIP-I and RIP-II packets will be
accepted.
Each layer3 switch running RIP has a route database, which contains all route entries for
reachable destination, and route table is built based on this database. When a RIP 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 abovementioned, RIP protocol allows route information discovered by the
other routing protocols to be introduced to the route table.
The operation of RIP protocol is shown below:
1. Enable RIP. 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.
2. 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 layer 3 switches
send triggered update packets to their neighbor layer 3 switches. After a sequence
of triggered update packet broadcast, all layer3 switches get and maintain the latest
route information.
In addition, RIP 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timeout mechanism for outdated route, that is, if a switch does not receive regular update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 (holddown
timer interval), it will delete that route.
15.3.2.1 RIP Configuration Task Sequence
1. Enable RIP (required)
(1) Enable/disable RIP module.
(2) Enable interface to send/receive RIP packets
2. Configure RIP parameters (optional)
(1) Configure RIP sending mechanism
a Configure specified RIP packets transmission address