3Com WX3000 operation manual

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host or router resides. For example, if the destination address is 129.102.8.10 and the mask is 255.255.0.0, the address of the network segment where the destination host or router resides is 129.102.0.0. A mask consists of some consecutive 1s, represented either in dotted decimal notation or by the number of the consecutive 1s in the mask.

Interface: It indicates through which interface IP packets should be forwarded to the destination.

Nexthop: It indicates the next router that IP packets will pass through to reach the destination.

Preference: There may be multiple routes with different next hops to the same destination. These routes may be discovered by different routing protocols, or be manually configured static routes. The one with the highest preference (the smallest numerical value) will be selected as the current optimal route.

According to different destinations, routes fall into the following categories:

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Subnet route: The destination is a subnet.

Host route: The destination is a host.

In addition, according to whether the network where the destination resides is directly connected to the router, routes fall into the following categories:

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Direct route: The router is directly connected to the network where the destination resides.

Indirect route: The router is not directly connected to the network where the destination resides.

In order to avoid an oversized routing table, you can set a default route. All the packets for which the router fails to find a matching entry in the routing table will be forwarded through this default route.

Figure 1-1 shows a relatively complicated internet environment, the number in each network cloud indicate the network address. Router G is connected to three networks, and so it has three IP addresses and three physical ports. Its routing table is shown in Figure 1-1.

Figure 1-1Routing table

Destination Network	Nexthop	Interface
11.0.0.0	14.0.0.1	3
12.0.0.0	14.0.0.1	3
13.0.0.0	16.0.0.1	2
14.0.0.0	14.0.0.3	3
15.0.0.0	17.0.0.2	1
16.0.0.0	16.0.0.2	2
17.0.0.0	17.0.0.1	1
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