Translator Device for Connecting Networks and Applications

D.

A gateway is used to connect two networks using dissimilar protocols at the lower layers or it could also be at the highest level of the protocol stack.

Important Note: For the purpose of the exam, you have to remember that a gateway is not synonymous to the term firewall.

The second thing you must remembers is the fact that a gateway act as a translation device.

It could be used to translate from IPX to TCP/IP for example.

It could be used to convert different types of applications protocols and allow them to communicate together.

A gateway could be at any of the OSI layers but usually tend to be higher up in the stack.

For your exam you should know the information below: Repeaters - A repeater provides the simplest type of connectivity, because it only repeats electrical signals between cable segments, which enables it to extend a network.

Repeaters work at the physical layer and are add-on devices for extending a network connection over a greater distance.

The device amplifies signals because signals attenuate the farther they have to travel.

Repeaters can also work as line conditioners by actually cleaning up the signals.

This works much better when amplifying digital signals than when amplifying analog signals, because digital signals are discrete units, which makes extraction of background noise from them much easier for the amplifier.

If the device is amplifying analog signals, any accompanying noise often is amplified as well, which may further distort the signal.

A hub is a multi-port repeater.

A hub is often referred to as a concentrator because it is the physical communication device that allows several computers and devices to communicate with each other.

A hub does not understand or work with IP or MAC addresses.

When one system sends a signal to go to another system connected to it, the signal is broadcast to all the ports, and thus to all the systems connected to the concentrator.

Repeater -

Bridges - A bridge is a LAN device used to connect LAN segments.

It works at the data link layer and therefore works with MAC addresses.

A repeater does not work with addresses; it just forwards all signals it receives.

When a frame arrives at a bridge, the bridge determines whether or not the MAC address is on the local network segment.

If the MAC address is not on the local network segment, the bridge forwards the frame to the necessary network segment.

Bridge -

Routers - Routers are layer 3, or network layer, devices that are used to connect similar or different networks.

(For example, they can connect two Ethernet LANs or an Ethernet LAN to a Token Ring LAN.) A router is a device that has two or more interfaces and a routing table so it knows how to get packets to their destinations.

It can filter traffic based on access control lists (ACLs), and it fragments packets when necessary.

Because routers have more network-level knowledge, they can perform higher-level functions, such as calculating the shortest and most economical path between the sending and receiving hosts.

Router and Switch -

Switches - Switches combine the functionality of a repeater and the functionality of a bridge.

A switch amplifies the electrical signal, like a repeater, and has the built-in circuitry and intelligence of a bridge.

It is a multi-port connection device that provides connections for individual computers or other hubs and switches.

Gateways - Gateway is a general term for software running on a device that connects two different environments and that many times acts as a translator for them or somehow restricts their interactions.

Usually a gateway is needed when one environment speaks a different language, meaning it uses a certain protocol that the other environment does not understand.

The gateway can translate Internetwork Packet Exchange (IPX) protocol packets to IP packets, accept mail from one type of mail server and format it so another type of mail server can accept and understand it, or connect and translate different data link technologies such as FDDI to Ethernet.

Gateway Server -

The following answers are incorrect: Repeater - A repeater provides the simplest type of connectivity, because it only repeats electrical signals between cable segments, which enables it to extend a network.

Repeaters work at the physical layer and are add-on devices for extending a network connection over a greater distance.

The device amplifies signals because signals attenuate the farther they have to travel.

Bridges - A bridge is a LAN device used to connect LAN segments.

It works at the data link layer and therefore works with MAC addresses.

A repeater does not work with addresses; it just forwards all signals it receives.

When a frame arrives at a bridge, the bridge determines whether or not the MAC address is on the local network segment.

If the MAC address is not on the local network segment, the bridge forwards the frame to the necessary network segment.

Routers - Routers are layer 3, or network layer, devices that are used to connect similar or different networks.

(For example, they can connect two Ethernet LANs or an Ethernet LAN to a Token Ring LAN.) A router is a device that has two or more interfaces and a routing table so it knows how to get packets to their destinations.

It can filter traffic based on access control lists (ACLs), and it fragments packets when necessary.

The device that is used to connect two networks or applications from layer 4 up to layer 7 of the ISO/OSI Model is called a gateway.

A gateway acts as a translator or a protocol converter between two networks that may use different communication protocols. It operates at the network layer (layer 3) and above, translating network protocols as well as application-layer protocols, such as HTTP, SMTP, FTP, and Telnet.

Gateways are typically used when two networks are incompatible with each other or use different communication protocols. For example, a company may use an Ethernet LAN for its internal network, while its partners or customers may use a different networking technology. In this case, a gateway can be used to translate between the two networks, allowing them to communicate with each other.

In addition to protocol translation, gateways can also provide security services such as encryption and decryption, access control, and authentication. They can also perform tasks such as data compression and decompression, caching, and traffic shaping.

Compared to other network devices like bridges, repeaters, and routers, gateways are more complex and expensive because they operate at higher layers of the ISO/OSI model and require more processing power and memory to perform their functions.