A gateway acts as a portal between two programs allowing them to share information by communicating between protocols on a computer or between dissimilar computers.
In enterprises, the gateway node often acts as a proxy server and a firewall. The gateway is also associated with both a router, which use headers and forwarding tables to determine where packets are sent, and a switch, which provides the actual path for the packet in and out of the gateway.
Types of gateways :
- LAN Gateways. LAN gateways are used when joining networks that use different protocols, such as when a backbone network provides an interconnection for all the networks attached to it.
- Electronic Mail Gateways. Electronic mail gateways translate messages from one vendor's messaging application to another's so that users with different e-mail applications can share messages over a network.
- Firewall. A firewall is a device that allows internal network users to access the Internet while blocking Internet users from accessing the internal network. A full-featured firewall provides advanced screening, authentication, and proxy services to keep hackers and attackers from reaching vulnerable internal systems.
- Proxy service. With a proxy service, the packet generated by an internal user never goes out over the Internet. Instead, the proxy service reads the packet and creates its own to send out over the network. Incoming packets are handled in the same way. They are never allowed through the proxy server as is.
- NAT (Network Address Translation). An NAT translates between internal and external IP addresses because internal network may have its own internal IP addressing scheme that does not comply with the Internet addressing scheme or is hidden for security reasons.
- Caching services. caches information that users have obtained from the Internet or external networks and keeps it available in case other users need that same information.
- Voice/Media Gateways. Voice is a streaming technology, while data is typically packetized. Media gateways, which are part of the softswitch architecture, provide an interface between the circuit-based PSTN and the packet-based Internet.