Tuesday, Jun 18th

Last update12:59:40 PM GMT

Hubs, Bridges, Switches and Routers

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Network ElementsThese are some of those network boxes which always confuse us with what function they perform :) Let’s try to clear up some air, from the most basic to the most advanced of these boxes



  • Its function is to repeat, i.e. forward every frame it receives to the output wire
  • It does not amplify the signal, only regenerates it by removing noise
  • It is bi-directional in nature
  • Useful if you want to increase the size/length of your Ethernet (cable)
  • There can be a maximum of 5 repeaters in an Ethernet


  • Hub is nothing more than a multiport repeater
  • It can be used to divide a single LAN into multiple levels of hierarchy
  • A hub takes the incoming data packet from a port and copies it out to all the other ports. It doesn't perform any filtering or redirection of data.
  • A good analogy for a hub is that of an Internet Chat room.  Everything that everyone types in the chat room is seen by everyone else. And, if there are too many people trying to chat things get bogged down; same thing happens with a Hub.

Both hub and repeater function at the Physical Layer (Layer 1) of the OSI model


  • A bridge is used to connect similar or dissimilar LANs
  • It is designed to store and forward frames
  • Bridges are Protocol independent and are transparent to End Systems, i.e. they don't know anything about protocols, they just forward data depending on the destination address in the data frame
  • A bridge operates at the layer 2 (and also layer 1 if it functions as a hub)
  • It uses a table of addresses for filtering and routing frames (remember at layer 2 we have frames, while at layer 3 packets). So if your frame does not have a valid address, it won’t be sent across the bridge
  • This address is the MAC (Media Access Control) address that is unique to each network adapter card.
  • With a Bridge, all your computers become connected in the same network subnet, so you can communicate between computers or share an Internet connection.
  • DHCP servers will work fine across Bridges, or if you assign your own IP addresses, you'll use the same first 3 "octets" of the IP address (Example: 192.168.0.X)
  • Bridges don't require programming.  They learn the addresses of the computers connected to them by listening to the data flowing through them.
  • Bridges are very useful for joining networks made of different media types together into larger networks, and keeping network segments free of data that doesn't belong in a particular segment.


  • Generally, a switch is nothing more than a fast bridge.
  • Switches have multiple ports with the same "flavor" connection (Example: 10/100BaseT)
  • They improve performance in a heavily loaded network by isolating data between 2 lightly used computers from data intended for a heavily used server.
  • "Auto sensing" switches also allow mixing of 10 and 100Mbps connections, without the slower 10Mbps transfer affecting the faster 100Mbps flow.


  • Routers are perhaps the most popular network elements, with almost everyone having one in their homes these days (btw, i pronounce them as 'rooters' :))
  • Routers also forward data packets from one place to another but they are Layer 3 devices, and forward data depending on the Network or IP address, rather than the Hardware (MAC) address.  For TCP/IP networks, this means the IP address of the network interface
  • Routers isolate each LAN into a separate subnet, so each network adapter's IP address will have a different third "octet" (Example: and are in different subnets)
  • They are required in large networks because the TCP/IP addressing scheme allows only 254 addresses per (Class C) network segment
  • Routers, like bridges, provide bandwidth control by keeping data out of subnets where it doesn't belong. However, routers need to be configured before they can get going, although once set up, they can communicate with other routers and learn the way to parts of a network that are added after the initial configuration


  • Gateways function at the Layer -7 Relay or Application Layer
  • The meaning of "gateway" has changed over the years and tends to depend on context. They generally convert one protocol to another or provide a conversion of packets between one system and a dissimilar other system. For example, a voice gateway may translate between VoIP and normal phone lines. 
  • Whenever you need a network change, like when voice travels from a mobile phone to a landline, gateways come into picture. They convert data understood by one system to the language of the other system, so they can communicate.

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