Routing Information Protocol (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 suitable for every TCP/IP environment. Before
using the RIP function in OMPROUTE, read RFCs 1058 and 1723 to decide
if RIP can be used to manage the routing tables of your network. For
more information about RFCs 1058 and 1723, see Related protocol specifications.
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, sets all routes through that
router to a metric of 16 (infinity), and stops using those routes
when routing IP packets. 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
- 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.
- 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.
For configuration information for RIP, see Steps for configuring OSPF and RIP (IPv4 and IPv6).