D-Link DES-3326S - Switch - Stackable Uživatelská příručka stáhnout pdf (Strana 128)

DES-3326S Layer 3 Fast Ethernet Switch User’s Guide

128 Switch Management and Operating Concepts

1. When OSPF is started, or when a change in the

routing information changes, the router

generates a link-state advertisement. This

advertisement is a specially formatted packet

that contains information about all the link-

states on the router.

2. This link-state advertisement is flooded to all

router in the area. Each router that receives the

link-state advertisement will store the

advertisement and then forward a copy to other

routers.

3. When the link-state database of each router is

updated, the individual routers will calculate a

Shortest Path Tree to all destinations − with the

individual router as the root. The IP routing

table will then be made up of the destination

address, associated cost, and the address of the

next hop to reach each destination.

4. Once the link-state databases are updated,

Shortest Path Trees calculated, and the IP

routing tables written − if there are no

subsequent changes in the OSPF network (such

as a network link going down) there is very little

OSPF traffic.

The Shortest Path Algorithm

The Shortest Path to a destination is calculated using the

Dijkstra algorithm. Each router is places at the root of a tree

and then calculates the shortest path to each destination based

on the cumulative cost to reach that destination over multiple

possible routes. Each router will then have its own Shortest

Path Tree (from the perspective of its location in the network

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D-Link DES-3326S - Switch - Stackable Uživatelská příručka Strana 128