Understanding the network.pdf - Back to Home

Today, RIP is considered by some to be antiquated and ineffective,
particularly RIPv1. Despite this belief, RIP is still common, especially
in old Novell NetWare shops, because IPX uses RIP for route
management. Another popular use for RIP is to redistribute routing
information from systems that only support RIP into another routing
protocol. RIP's real value to us is that it illustrates all the basic
elements of a dynamic routing protocol.
NOTE
Extended RIP (ERIP) is also available on some platforms. ERIP
extends the network diameter to 128 hops.
RIP uses only one metric to determine the best route: hop count. The
term hop refers to the unit of distance between forwarding points,
such as end-stations or routers. Corresponding to RIP's limited
network topology, RIP supports hop counts with a range from 1
(directly connected) to 16 (unreachable network). This distance
limitation constrains RIP's usage in large enterprise networks. But,
RIP was not designed and should not be used to manage routing in an
enterprise. RIP was designed to be used in networks of limited size
using similar Layer 2 transport, which means that it does work well in
small LAN networks.
RIP is a distance vector protocol, based on the vector distance
algorithm (described in the "Distance Vector Protocols" section earlier
in the chapter). Distance vector messages are sent as value pairs. The
first value is the vector or destination. The second value is the
distance or hop count. After the router comes online, it builds its local
routing table and then joins the RIP process by sending a RIP message
with the request command flag set. The router listens for responses
from the other directly connected routers, which contain the other
routers'routing tables.
Using the example shown in Figure 8.7, Router E's initial routing table
would look like what is shown in Table 8.4.