Huawei Quidway S3900 Series Operation Manual page 289

Operation Manual – Routing Protocol
Quidway S3900 Series Ethernet Switches-Release 1510
Network mask: Along with the destination address, it identifies the address of the
network segment where the destination host or router resides. By performing
"logical AND" between destination address and network mask, you can get the
address of the network segment where the destination 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.
Output interface: It indicates through which interface IP packets should be
forwarded to reach the destination.
Next hop address: It indicates the next router that IP packets will pass through to
reach the destination.
Preference of the route added to the IP routing table: 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:
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 falls into the following categories:
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 1-2 shows a relatively complicated internet environment, the number in each
network cloud indicate the network address and "R" represents a router. The router
R8 is connected to three networks, and so it has three IP addresses and three
physical ports. Its routing table is shown in Figure 1-2.
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Chapter 1 IP Routing Protocol Overview