RIP is an Interior Gateway Protocol (IGP) designed to manage a relatively small network. RIP is based on the Bellman-Ford or the distance-vector algorithm. RIP has many limitations and is not suited for every TCP/IP environment. You may wish to read more about RIP in RFCs 1058 and 1723.
RIP uses the number of hops, or hop count, to determine the best possible route to a host or network. The term hop count is also referred to as the metric. In RIP, a hop count of 16 means infinity, or that the destination cannot be reached. This limits the longest path in the network that can be managed by RIP to 15 gateways.
A RIP router broadcasts routing information to its directly connected networks every 30 seconds. It receives updates from neighboring RIP routers every 30 seconds and uses the information contained in these updates to maintain the routing table. If an update has not been received from a neighboring RIP router in 180 seconds, a RIP router assumes that the neighboring RIP router is down and sets all routes through that router to a metric of 16 (infinity). If an update has still not been received from the neighboring RIP router after another 120 seconds, the RIP router deletes from the routing table all of the routes through that neighboring RIP router.
RIP Version 2 is an extension of RIP Version 1 and provides the following features:
· Route Tags to provide EGP-RIP and BGP-RIP interactions: The route tags are used to separate internal RIP routes (routes for networks within the RIP routing domain) from external RIP routes, which may have been imported from an EGP (external gateway protocol) or another IGP. OMPROUTE does not generate route tags, but preserves them in received routes and readvertises them when necessary.
· Variable subnetting support: Variable length subnet masks are included in routing information so that dynamically added routes to destinations outside subnetworks or networks can be reached.
· Immediate Next Hop for shorter paths: Next hop IP addresses, whenever applicable, are included in the routing information to eliminate packets being routed through extra hops in the network. OMPROUTE does generate immediate next hops, but does preserve them if they are included in the RIP packets.
· Multicasting to reduce load on hosts: IP multicast address 224.0.0.9, reserved for RIP Version 2 packets, is used to reduce unnecessary load on hosts which are not listening for RIP Version 2 messages. This support is dependent on interfaces that are multicast-capable.
· Authentication for routing update security: Authentication keys can be configured for inclusion in outgoing RIP Version 2 packets. Incoming RIP Version 2 packets are checked against the configured keys.
· Configuration switches for RIP Version 1 and RIP Version 2 packets: Configuration parameters allow for controlling which version of RIP packets are to be sent or received over each interface. Supernetting support: The supernetting feature is part of Classless InterDomain Routing (CIDR).
· Supernetting provides a way to combine multiple network routes into fewer supernet routes, thus reducing the number of routes in the routing table and in advertisements.
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