H3C S5500-SI Series, Operation Manual

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IP Routing Overview
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IP Routing and Routing Table
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Routing Protocol Overview
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Displaying and Maintaining a Routing Table
The term “router” in this document refers to a router in a generic sense or a Layer 3 switch.
IP Routing and Routing Table
Routing
Routing in the Internet is achieved through routers. Upon receiving a packet, a router finds an optimal
route based on the destination address and forwards the packet to the next router in the path until the
packet reaches the last router, which forwards the packet to the intended destination host.
Routing Table
Routing table
Routing tables play a key role in routing. Each router maintains a routing table, and each entry in the
table specifies which physical interface a packet destined for a certain destination should go out to
reach the next hop (the next router) or the directly connected destination.
Routes in a routing table can be divided into three categories by origin:
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Direct routes: Routes discovered by data link protocols, also known as interface routes.
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Static routes: Routes that are manually configured.
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Dynamic routes: Routes that are discovered dynamically by routing protocols.
Contents of a routing table
A routing table includes the following key items:
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Destination address: Destination IP address or destination network.
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Network mask: Specifies, in company with the destination address, the address of the destination
network. A logical AND operation between the destination address and the network mask yields
the address of the destination network. For example, if the destination address is 129.102.8.10 and
the mask 255.255.0.0, the address of the destination network is 129.102.0.0. A network mask is
made of a certain number of consecutive 1s. It can be expressed in dotted decimal format or by the
number of the 1s.
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Outbound interface: Specifies the interface through which the IP packets are to be forwarded.