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| Networking : Tricky Ones : Differences between a Bridge & a Switch |
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| Question: | Could anyone let me know what a Bridge is & also the difference between Bridge & a Switch? |
| Answer: | Now, your doubt seems very reasonable to me. I bet even the best of networking professionals will not be able to clearly define and list all the differences between each of these devices(repeater,hub,bridge,switch,router...).
Anyways, coming to your question let me give it a try - BRIDGE - Imagine a real bridge. Now suppose that persons A & B reside on one side of the bridge and C & D on the other side. So, if A wants to meet B would you think A would travel all across the bridge to the other side to meet B. (Answer - NO). A bridging device functions similarly. It learns about various nodes on either side of the bridge and only passes(broadcasts) traffic to the other side ONLY when required. In other words, a bridge creates separate collision domains and merges broadcast domains while with a switch you can have separate collision as well as separate "configurable" broadcast domains. I say "configurable" because with a switch you can create zones called VLANS and place only those nodes that you would want to communicate with each other in one brodcast domain. Creation of VLANS cannot be accomplished using a bridge. There are lot more differences between these two and significant ones among those are - a) Bridges are used to interconnect different types of networks(For example a wired ethernet segment with a wireless 802.11b/g or a token ring network etc..) b) You can split the bandwidth amongst the nodes using a switch while it is not easily accomplished using a bridge. c) A switch is also called a multi-port bridge because a (hardware) bridge is formed between any two ports on a switch depending on the need as determined by the switch's forwarding decision. d) Switches primarily rely on hardware for intelligence while bridges use software based algorithms to maintain the forwarding tables. e) Bridges mostly just use one type of mechanism for switching the frames i.e., "Store and Forward", in which the bridge has to wait until it recieves the complete frame and check for errors before it could make the forwarding decision while a switch uses "Store & Fwd", "Cut-Through" (waits until it receives first 64K bytes and checks for errors instead of waiting for the entire frame) & "Fast Forward"(no wait & no error checking) mechanisms. Few more points - + To qualify a switch as a "layer 3" switch, it should be capable of doing ISL trunking to "route" between VLANS using the tag info associated to the frame. + Repeaters & Hubs are dumb devices. The former amplifies a signal alongwith noise while the latter is just a distribution point with zero intelligence. Hmmn..that turned out to be a long one..hope that helps to an extent. |
| last updated 11.11.2003 | |
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