D-Link DES-3326SR, Руководство пользователя

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DES-3326SR Layer 3 Fast Ethernet Switch User’s Guide
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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.
Packet Fragmentation and Reassembly
TCP/IP can be used with many different types of networks, but
not all network types can handle the same length packets.
When IP is transmitting large files, large packets are much
more efficient than small ones. It is preferable to use the
largest possible packet size, but still be able to cross networks
that require smaller packets.
To do this, IP can ‘negotiate’ packet size between the local and
remote ends of a connection. When an IP connection is first
made, the IPs at both ends of the connection state the largest
packet they can handle. The smaller of the two is selected.
When a IP connection crosses multiple networks, it is possible
that one of the intermediate networks has a smaller packet size
limit than the local or remote network. IP is not able to