Table 3-1
shows the default administrative distance for selected routing information sources.
256k
T1
T1 256k
RIP
Hop Count
OSPF
COST
Bandwidth
Delay
Load
Reliability
EIGRP
A
B
OSPF Advertises
172.16.0.0
EIGRP Advertises
172.16.0.0
A
Network
172.16.0.0
Reviewing Dynamic Routing 103
If nondefault values are necessary, you can use Cisco IOS Software to con?¬?gure administrative
distance values on a per-router, per-protocol, and per-route basis.
Understanding Distance Vector Routing Protocols
Distance vector??“based routing algorithms (also known as Bellman-Ford-Moore algorithms) pass
periodic copies of a routing table from router to router and accumulate distance vectors. (Distance
means how far, and vector means in which direction.) Regular updates between routers
communicate topology changes.
Each router receives a routing table from its direct neighbor. For example, in Figure 3-5, Router
B receives information from Router A. Router B adds a distance vector metric (such as the number
of hops), increasing the distance vector. It then passes the routing table to its other neighbor,
Router C. This same step-by-step process occurs in all directions between direct-neighbor routers.
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