3com 5500-ei pwr Instruccion De Instalación

 

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Taking no account of area partition, the routing calculation process of the OSPF protocol is as follows: 

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Each OSPF-supported router maintains a link state database (LSDB), which describes the 

topology of the whole AS. According to the network topology around itself, each router generates a 

link state advertisement (LSA). Routers on the network exchange LSAs with each other by 

transmitting protocol packets. Thus, each router receives the LSAs of other routers and all these 

LSAs form the LSDB of the router. 

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An LSA describes the network topology around a router, whereas an LSDB describes the network 

topology of the whole network. Routers can transform the LSDB to a weighted, directed graph, 

which reflects the real topology of the whole network. All routers get exactly the same weighted, 

directed graph. 

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According to the weighted, directed graph, each router uses the shortest path first (SPF) algorithm 

to calculate the shortest path tree with itself as the root. The tree shows the routes to the nodes in 

the autonomous system. External routes are leaf nodes, which are marked with the routers from 

which they are advertised to record information outside the AS. The routing tables obtained by 

different routers are different. 

Furthermore, to enable individual routers to broadcast their local status information (such as available 

interface information and reachable neighbor information) to the whole AS, routers in the AS should 

establish adjacencies among them. In this case, the route changes on any router will result in multiple 

transmissions, which are unnecessary and waste the precious bandwidth resources. To solve this 

problem, designated router (DR) and backup designated router (BDR) are defined in OSPF. For details 

about DR and BDR, see section 

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OSPF supports interface-based packet authentication to guarantee the security of route calculation. In 

addition, it transmits and receives packets in multicast (224.0.0.5 and 224.0.0.6). 

A set of routers using the same routing protocol to exchange routing information constitute an 

Autonomous System (AS). 

To run OSPF, a router must have a router ID. A router ID can be configured manually. If no router ID is 

configured, the system will automatically select an IP address from the IP addresses of the interfaces as 

the router ID. A router ID is selected in the following way: 

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If loopback interface addresses are configured, the system chooses the latest configured loopback 

interface IP address as the router ID. 

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If no loopback interface is configured, the first configured IP address among the IP addresses of 

other interfaces will be the router ID. 

OSPF uses five types of packets: