TMS zl Management and Configuration Guide ST.1.1.100226

9-13
Routing
Dynamic Routing
Table 9-2. RIP and OSPF Comparison
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.
Option RIP OSPF
Metric computation and
route selection
Number of hops to the destination. • Inverse bandwidth
• Type of service (ToS) (rarely used)
Information in updates Routers send the complete RIP routing
table.
Different types of LSAs include different
information:
• A link and its status:
– link to a network
– link to another router
• Router ID of every router in a multi-access
network
• Summary route to a range of networks in an
area (sent by ABRs)
• Route to autonomous system border router,
or ASBR (sent by ABRs)
• External routes or default route for external
traffic (sent by ASBRs)
The routers and router
interfaces that send and
receive updates
• All router interfaces on RIP networks.
• The interface that receives a route
advertises it as unreachable (split
horizon with poison reverse).
• Passive interfaces receive updates
but do not send them.
• In point-to-point networks, neighboring
routers exchange LSAs.
• In multi-access networks, all routers send
LSAs to a DR and backup DR (BDR) and
receive LSAs from a DR.
• ABRs send route summaries into stub areas.
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