Information Technology Reference
In-Depth Information
•
OSPF (open shortest path first).
•
RIP (routing information protocol).
Most routers support RIP and EGP. In the past, RIP was the most popular router protocol
standard. Its widespread use is due, in no small part, to the fact that it was distributed along
with the Berkeley Software Distribution (BSD) of UNIX (from which most commercial ver-
sions of UNIX are derived). It suffers from several disadvantages and has been largely re-
placed by OSFP and EGB. These newer protocols have the advantage over RIP in that they
can handle large internetworks, as well as reducing routing table update traffic.
RIP uses a distance vector algorithm which measures the number of network jumps
(known as hops), up to a maximum of 16, to the destination router. This has the disadvantage
that the smallest number of hops may not be the best route from source to destination. The
OSPF and EGB protocol uses a link state algorithm that can decide between multiple paths to
the destination router. These are based, not only on hops, but on other parameters such as
delay capacity, reliability and throughput.
With distance vector routing each router maintains tables by communicating with neigh-
bouring routers. The number of hops in its own table are then computed as it knows the
number of hops to local routers, as illustrated in Figure 25.11. Unfortunately, the routing
table can take some time to be updated when changes occur, because it takes time for all the
routers to communicate with each other (known as slow convergence).
Router Hops
1
1
3
1
4
2
5
3
Router
2
Router Hops
1
Router Hops
1
1
2
2
1
2
2
4
1
3
1
5
2
5
1
Router
1
Router
3
Router
4
Router Hops
2
1
3
1
4
2
5
3
Router Hops
1
Router
5
Routing table for
Router 1 is send to
neighbouring routers
2
2
2
3
2
4
1
Figure 25.11
Routing tables with number of hops
25.5 Network cable types
The cable type used on a network depends on several parameters, including:
•
The data bit rate.
