Gateways

Gateways

The term “gateway” originally was used in the Internet protocol suite to refer to a router. Today, the term “gateway” more commonly refers to a system functioning at the top levels of the OSI model that enables communication between dissimilar protocol systems. A gateway generally is dedicated to a specific conversion, and the exact functioning of the gateway depends on the protocol translations it must perform. Gateways commonly function at the OSI Application layer.

Gateways connect dissimilar environments by removing the layered protocol information of incoming packets and replacing it with the packet information necessary for the dissimilar environment (see Figure 6.12).

Gateways can be implemented as software, hardware, or a combination of both.

The NetBIOS Gateway

A previous sidebar described how Windows NT 4.0 RAS can act as an IP or an IPX router. RAS’s NetBIOS gateway is an even more powerful feature. Not only does the NetBIOS gateway forward remote packets to the LAN, but it also acts as a gateway, providing NetBEUI clients with access to the LAN even if the LAN uses only TCP/IP or IPX/SPX.

The NetBIOS gateway (see Figure 6.13) is very much like the gateways described in this section. The NetBIOS gateway accepts a packet from the remote computer using one protocol (NetBEUI) and converts the packet, stripping incompatible protocol headers and replacing them with the headers the packet will need to circulate under a different protocol.