Network Devices Bridge, Router and Gateway

Bridges operate on both data link and physical layer of the OSI model. Bridges can be used to divide a large network into segments.  Bridges contain logic that allows them to keep the traffic for each segment separate. When a new frame enters to a bridge, the bridge not only regenerate the frame but it also checks the address of the destination and forwards the new copy only to the segment to which the destination address belongs.

Bridge in a network

There exist different type of bridges some of them are;

Simple bridge: This links only two segments and contains a table that lists the addresses of all nodes included in each of the segment. The operator needs to setup the table manually before the simple bridge can

use. If any node removes from a segment then it must manually remove from the table. It is time consuming and cause to errors.

Multiport Bridge: Can be used to connect more than two LANs.

Transparent Bridge  

This type of bridges does not require an administrator; it builds its own table of node addresses on its own as it performs bridge functions. When first installed to a network its table is empty. As it encounters each packet, it checks the destination to decide where to send the packet. If it does not yet recognize the destination address, it floods the packet to all of the stations on both segments. It uses the source address to build its table. As it processes a packet, it checks the source address and adds it to the table and record the segment of the address. As time goes, the bridge has a table with full details. A transparent bridge is also self-updating.

Routers

A router is a device that forwards data packets between computer networks. The router operates on the first three layers of the OSI model. Routers transmit packets among multiple inter-connected networks. Routers use routing algorithms for packet’s route determination process. We already discussed several routing algorithms.

Gateway

 A gateway is an internetworking system capable of joining two networks that use different base protocols. Gateway operates on all seven layers of OSI model. A gateway can accept a packet from one protocol (eg: TCP/IP) and format it to a packet as per the requirement of another entirely different protocol (eg: Apple talk) before forwarding the packet. A gateway also capable to adjust rate at which the data transfer, size of the packet, format of the packet and so on. A gateway is usually a software installed with in a router.

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