52
Chapter 2
Protocol Attributes
This finishes our discussion on some of the protocols present in the IP
suite. We now move on to the routing protocol RIP.
Routing Information Protocol (RIP)
The Routing Information Protocol (RIP) is a distance-vector routing proto-
col. The metrics used by RIP is the hop count, which specifies the number of
steps or nodes that a packet must transit in order to reach the destination
host.
The major problem with RIP is that it has a hop-count limit. The maxi-
mum hop limit that the packet can travel is 15 hops. If the destination
exceeds 15 hops, the destination is tagged as unreachable. This is good for
small networks because it also helps prevent the count-to-infinity in a rout-
ing loop, but it is inefficient for today's Internet.
Now that you know a little about how RIP works, look at the packet
structure in Figure 2.11. The packet is 24 bytes long. RIP uses five parame-
ters to define packet information. The packet is divided into nine fields, and
zeroes are used to pad the packet to the full 24 bytes.
F I G U R E 2 . 1 1
RIP packet structure
Table 2.6 shows a legend of the five different parameters used within the
RIP packet. As you can see from the figure, some of the fields are empty.
They are just padded with zeroes.
T A B L E 2 . 6
RIP Parameters
Parameter
Key
Description
A
Command
: Identifies the packet as a request (value=1) or a re-
sponse (value=2). Requests tell the receiving router to send
its route table information. Response packets include the
route table information.
23
20
16
12
8
6
4
2 1 0
F
0
0
E
0
0
B A
D
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