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Thread: Confused about bridge and router

  1. #1
    Junior Member
    Join Date
    May 2002

    Confused about bridge and router

    heloo guys i am a little big confused about the use and working of the brighe and the router.
    according to me.
    Birdge is used to connect two networks having the same protocol but having two different network Id's
    Router is a complex device than a bridge and used to route a packet through a complex network to the destination using the best known path.

    If u culd help me with givving ur ideas and some gud links i will be very thankfull to u
    thanx in advance

  2. #2
    Senior Member
    Join Date
    Jul 2004
    some gud links
    Here's about 92,000 bridging and router links

    Happy reading, hope these are gud links.

    And some tutorials

  3. #3
    Senior Member
    Join Date
    Aug 2001
    heres a very brief rundown of what i can remember from my uni studies last year about this stuff:
    bridges, like you mention connect 2 networks, the bridge knows about what packets are meant for each network, by either IP or MAC addy's (nt sure which), so if a packet goes from network A to network B, the bridge sends it across.

    If a packet goes from a PC on network A to another on network A, it stays on network A

    Routers can be used to send data to different networks, usually more than 2, the router knows about which networks can be accessed on each LAN interface and send the packets onto the apropriate interface so that they get to the destination. eg:


    INF A

    The router generally knows what LAN's are on INF A, B and C in the Routing table

    so if a PC on INF A wants to send something to INF B or INF C, it forwards it onto the appropriate interface on the router itself. I believe this is correct, anyone please correct me if i'm wrong here..

    hoipe this is of a bit of help to you. (apologies for the badly drawn grafix)
    Just wait till i get my slappin gloves on.....

  4. #4
    Senior Member
    Join Date
    Apr 2004
    just different devices

    Bridges - act at layer 2. They dont care about "protocols". Bridges only "understand" ethernet, Token-ring, ppp, etc frames. What is inside doesnt matter. Its is used to connect layer 2 networks
    Routers - act at layer 3. They care about protocols that you know: TCP/IP, IPX, etc... In fact, standard routing only act at network layer, so it takes care of "IP" (TCP is inside and doesnt matter) ICMP, etc...
    Meu sítio

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  5. #5
    Senior Member
    Join Date
    Jan 2003
    Let me add to the confusion.

    First..a switch is nothing but a multiport bridge.

    Switches do their dirty work in hardware. Routers do it in software. I run numerous Layer 3 and Layer 4-7 switches. They are completely capable of understanding IP. They 'route' between different networks. I can create access control lists to block or allow certain ports (Layer 4) I can even load balance based on application. Why these aren't routers, however, is that they are doing it all at the chip and board level. Traditional routers have to look to the software to make routing decisions. This injects a wee bit of latency into your data flow.

    Now....on a little network is a user going to see the difference between being connected to a router or a switch? No way. When I say latency, I mean milliseconds. However, when multi-casting video streams to dozens or even hundreds of machines on different networks.......Man am I glad I'm switching.

    To further confuse....routers 'switch' too. That process takes place internally and is usually invisible to even the admin. You have to dig for it. \

    Anyway....what I'm trying to get at, is that where it's feasible (ie multiple ethernet networks) it is better to switch (bridge) than route as far as performance is concerned.

  6. #6
    Senior Member
    Join Date
    Feb 2004
    Near Manchester (England)
    I think cacosapo has it. There is confusion, generally, around what a bridge really is in the networking world. Truly a bridge works at the network layer, just above the physical layer in the ISO model.

    Here are some links to clear things up:



    Home Networking:

    hope they work!
    Tomorrow is another day for yesterdays work!

  7. #7
    Join Date
    Jul 2003
    Hey ...
    why make this simple guy realise that he has made a mistake by asking us a simple question.

    though Hunt_guy you could have searched it over google (as link above) i will still make it simpler for you ..

    1 Bridging operates at Layer 2 , in early days softwares were used to configure and then the technology advanced and it could be then done through hardware known as Application Specific Integrated Circuits (ASIC) technology. They just understand MAC add. and pass it through. There are categories to it as well you can search google/cisco for more info there are tons of docs on it :-)

    2 Routing as said above is Layer 3, (network for OSI Model and Internetwork for DoD Model) which is more intelligent works with IP Addresses. and then there is whole story ahead.

    Simply any device to communicate will talk at layer 2 and layer 3 and above as well, just that each layers understands only it peer language :-) ..

    Trying using Interconnecting Cisco Network Devices for a better understanding of these things.. its the basic and best place i think to start.


  8. #8
    Senior Member
    Join Date
    Jul 2004
    why make this simple guy realise that he has made a mistake by asking us a simple question.
    If it was simple for him, he wouldn't of asked. Sometimes it's better to get an answer real time
    from a forum like this one, than it is to ask a machine.

    What was the mistake anyway?

  9. #9
    Junior Member
    Join Date
    Aug 2004
    bridge is a level 2 connector and router is a level 3 device
    bridge forward frame by the mac address
    router forward packag by the ip address
    hope it helps

  10. #10
    Junior Member
    Join Date
    Oct 2001
    I think most of the basics have been covered, however one key point to remember: Bridges/Switches cannot route data over different networks, whereas router can.

    Because bridges (or now known as switches) work at the data link layer they can only see MAC addresses, hence cannot route between networks as MAC addresses do not have any information about which network a host is on. On the other hand, because routers route traffic using the network layer hence use IP they able to route traffic to different networks because IP provides a network and host address i.e. for the address, the network portion is 192.168.0 and the host address is 1.


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