TMS zl Management and Configuration Guide ST.1.1.100430

9-13
Routing
Dynamic Routing
Advantages and Disadvantages of Routing Protocols
Dynamic routing can provide reliable routes. OSPF, for example, can select
routes according to fairly sophisticated criteria, such as link state and band-
width. The best route at one moment may not always be the best route, and
dynamic routing protocols can track which route is best and when. Dynamic
routing also adapts well to changes in network topology, including node
failures as well as network expansion.
On the other hand, routing protocols consume bandwidth as routers exchange
updates and CPU processes as routers calculate the best routes. In addition,
a router that has been carelessly configured may send updates to unauthorized
devices, creating a security vulnerability. However, a well-designed network
eliminates many of these problems.
Table 9-3 lists some advantages and disadvantages of RIP and OSPF. As you
can see, each protocol provides different best uses. Keep in mind that proto-
cols work in conjunction with each other.
Table 9-3. Advantages and Disadvantages of RIP and OSPF
The intervals when routers
send and receive updates
• Routers send updates every 30
seconds.
• Routers send updates immediately
after a change in network topology
(triggered updates).
• Neighbors and DRs send LSAs:
– Not more than every 5 seconds
– Not less than every 30 minutes
– when topology changes
• Routers send:
– An ACK when they receive an LSA
– A hello every 10 seconds
Option RIP OSPF
Protocol Advantages Disadvantages Uses
RIP • Configuration is simple.
• RIP v2 can communicate with
an external network.
• Convergence is relatively slow.
• Metric is based only on hop
count.
• If used to connect to an ISP, the
ISP must redistribute the
routes into BGP.
•LANs
• Simple WANs
• Connecting to an external
network
• Not used over dial-up
connections
OSPF • Accurate routes take link
speed and cost into account.
• Convergence is fast.
• Overhead is as low as RIP if the
network is well-designed.
• Configuration is complicated.
• Overhead can be high.
• OSPF cannot be used as an
EGP without redistribution.
• More extensive LANs and
WANs
• Not used over dial-up
connections