DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
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.
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.
108 | Switch Management and Operating Concepts |
