Gateway (telecommunications)

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• Gateways, also called protocol converters, can operate at any network layer. The activities of a gateway are more complex than that of the router or switch as it communicates using more than one protocol.
• In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy server and a firewall server. A gateway is often associated with both a router, which knows where to direct a given packet of data that arrives at the gateway, and a switch, which furnishes the actual path in and out of the gateway for a given packet.
• On an IP network, clients should automatically send IP packets with a destination outside a given subnet mask to a network gateway. A subnet mask defines the IP range of a private network. For example, if a private network has a base IP address of 192.168.0.0 and has a subnet mask of 255.255.255.0, then any data going to an IP address outside of 192.168.0.X will be sent to that network's gateway. While forwarding an IP packet to another network, the gateway might or might not perform Network Address Translation.
• A gateway is an essential feature of most routers, although other devices (such as any PC or server) can function as a gateway.

lmz:网关是第四层设备；网桥是第二层设备。

A default gateway in computer networking is the node that is assumed to know how to forward packets on to other networks. Typically in a TCP/IP network, nodes such as servers, workstations and network devices each have a defined default route setting, (pointing to the default gateway), defining where to send packets for IP addresses for which they can determine no specific route. The gateway is by definition a router.

In a home or small office environment, the device, such as a DSL router or cable router that connects the local network to the Internet will act as the default gateway for all network devices. In enterprise systems, there may be many internal network segments. A device wishing to communicate with an Internet address for example, will forward the packet to the default gateway for their segment. This in turn may pass the packet to a series of further default gateways before it leaves the enterprise. In such a situation, each gateway node may also act as a proxy server and a firewall.

tags:wikipedia