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status.
There two versions of RIP, version 1 and version 2. RFC1058 introduces RIP-I protocol,
RFC2453 introduces RIP-II, which is compatible with RFC1723 and RFC1388. RIP-I updates
packets by packets broadcast, subnet mask and authentication is not supported. Some fields in
the RIP-I packets are not used and are required to be all 0’s; for this reason, such all 0's fields
should be checked when using RIP-I, the RIP-I packets should be discarded if such fields are
non-zero. RIP-II is a more improved version than RIP-I. RIP-II sends route update packets by
multicast packets (multicast address is 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. ES4624-SFP/ES4626-SFP switch 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 above mentioned, RIP protocol allows route information discovered by the other
routing protocols to be introduced to the route table. It can also be as the protocol exchanging
route messages with CE on PE routers, and supports the VPN route/transmitting examples.
The operation of RIP protocol is shown below:
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.
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, 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.
1.4.2 RIP Configuration Task List