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Configuring DECnet Services

1-6

308619-14.00 Rev 00

Listening Process

The router periodically receives Hello messages from its adjacent routers,

informing it of their identity and of the circuits the router can use to reach the

adjacent nodes. The router stores this information in an adjacency table, thus

creating a database of next hops to use to forward data packets. A hop is the

logical distance between two nodes.

Decision Process

The router calculates the least-cost paths from itself to all other systems it can

reach, using information it receives from other routers and stores in routing tables.

If the least-cost path is disabled, or a node fails, the router finds an alternate path,

if one exists.

Site Manager assigns every circuit on a DECnet network a default cost. During the

decision process, the router running DECnet calculates the total path cost of

forwarding a datagram along each possible path toward its destination. The total

path cost is the sum of the costs of the outbound circuits that make up the path

(Figure 1-3)

. The least-cost path is the one that the router prefers.

Figure 1-3. Calculating the Least-Cost Path

Cost from A to B = 12

Cost from B to A = 15

Router

End Node

Key

DEC0003A

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