OSI Layer 3: Routed and Routing Protocols
53
Interior Gateway Routing Protocol (IGRP)
The Interior Gateway Routing Protocol (IGRP) is a Cisco proprietary rout-
ing protocol that uses a distance-vector algorithm because it uses a vector (a
one-dimensional array) of information to calculate the best path. This vector
consists of four elements:
Bandwidth
Delay
Load
Reliability
MTU, or maximum transmission unit, information is included in the final
route information, but it is not used as part of the vector of values when cal-
culating the metric. IGRP is intended to replace RIP and create a stable,
quickly converging protocol that will scale with increased network growth.
IGRP Features and Operation
IGRP has several features included in the algorithm--these features and brief
descriptions can be found in Table 2.7. The features were added to make
IGRP more stable, and a few were created to deal with routing updates and
make network convergence happen faster.
B
Version number
: Specifies the version of RIP being used.
D
Address family identifier
: Address family type. This
means which protocol is carrying the RIP packet.
E
Address
: The 32-bit IP address.
F
Metric
: The hop count to the destination system.
T A B L E 2 . 6
RIP Parameters (continued)
Parameter
Key
Description
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