D-Link DES-3326 User Manual - page 108
DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
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Switch Management and Operating Concepts
to any other system, but when packets must cross other networks
to reach a destination on a remote network, these packets must be
handled by gateways (also called routers).
Gateways connect a network with one or more other networks.
Gateways can be a computer with two network interfaces or a
specialized device with multiple network interfaces. The device is
designed to forward packets from one network to another.
IP routing is based on the network address of the destination IP
address. Each computer has a table of network addresses. For
each network address, a corresponding gateway is listed. This is
the gateway to use to communicate with that network. The
gateway does not have to be directly connected to the remote
network, it simply needs to be the first place to go on the way to
the remote network.
Before a local computer sends a packet, it first determines whether
the destination address is on the local network. If it is, the packet
can be sent directly to the remote device. If it is not, the local
computer looks for the network address of the destination and the
corresponding gateway address. The packet is then sent to the
gateway leading to the remote network. There is often only one
gateway on a network.
A single gateway is usually defined as a default gateway, if that
gateway connects the local network to a backbone network or to
the Internet. This default gateway is also used whenever no
specific route is found for a packet, or when there are several
gateways on a network.
Local computers can use default gateways, but the gateways
themselves need a more complete routing table to be able to
forward packets correctly. A protocol is required for the gateways
to be able to communicate between themselves and to keep their
routing tables updated.