Route Selection Through The Routing Table - Huawei Quidway S3900 Series Operation Manual

Operation Manual – Routing Protocol
Quidway S3900 Series Ethernet Switches-Release 1510
Host A
Host C
Figure 1-1 Route segment
The number of route segments on the path between a source and destination can be
used to measure the "length" of the path. As the sizes of networks may differ greatly,
the actual length of router segments may be different from each other. Therefore, you
can put different weights to different route segments (so that, for example, a route
segment can be considered as two segments if the weight is two), In this way, the
length of the path can be measure by the number of weighted route segments.
If routers in networks are regarded as nodes in networks and route segments in the
Internet are regarded as links in the Internet, routing in the Internet is similar to that in
a conventional network.
Routing through the shortest route is not always the most ideal way. For example,
routing across three high-speed LAN route segments may be much faster than
routing across two low-speed WAN route segments.

1.1.2 Route Selection through the Routing Table

The key for a router to forward packets is the routing table. Each router maintains a
routing table. Each entry in this table contains an IP address that represents a
host/subnet and specifies which physical port on the router should be used to forward
the packets destined for the host/subnet. And the router forwards those packets
through this port to the next router or directly to the destination host if the host is on a
network directly connected to the router.
Each entry in a routing table contains:
Destination address: It identifies the address of the destination host or network of
an IP packet.
Route
Segment
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1-2
Chapter 1 IP Routing Protocol Overview
Host B