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6755 Views 10 Replies Latest reply: Apr 15, 2011 8:49 AM by jk RSS

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Difference between layer 2, layer 3, Multi-layer and layer 4 Switch ?

Mar 31, 2011 9:21 PM

Arul 149 posts since
Dec 9, 2010

Can anyone explain the Difference between layer 2, layer 3, Multi-layer and layer 4 Switch ?

  • Keith Barker - CCIE RS/Security, CISSP 5,327 posts since
    Jul 3, 2009

    Hello Arul-

     

    Great question.

     

    A layer 2 switch, makes forwarding decisions based on L2 (MAC) addresses.  We would normally just call this device a switch.

     

    A layer 3 switch, makes forwarding decisions based on L3 (IP) addresses.  If we aren't trying to sell anything, this would normally call this device a router.

     

    A layer 4 switch, would take into consideration L4 information regarding forwarding/filtering of data.   We could say that a router with ACLs or Policy Based Routing that look at L4 information regarding segments of data is a L4 device.

     

    An example of a multilayer switch, would be a Cisco 3560, that can do L2 switching, L3 routing, and can involve the L4 content regarding forwarding, dropping, prioritizing, packets carrying specific L4 information (such as a specific L4 protocol of TCP or UDP or ICMP, or a specific port such as TCP:23 or TCP:80.

     

    Best wishes,

     

    Keith

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  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,426 posts since
    Oct 7, 2008

    Arul wrote:

     

    Can anyone explain the Difference between layer 2, layer 3, Multi-layer and layer 4 Switch ?

     

    A switch is layer 2.  Period.

     

    It may have higher functions, and ASICs built to help things at the hardware level...  That's the part that makes it "multilayer".  But a switch is a layer 2 device.

     

    Just because you have a super-dooper sports car with nitro boost doesn't mean it's not still a car.   it's just a car that has extra features. 

     

    HTH,

     

    Scott

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  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,426 posts since
    Oct 7, 2008

    Ahhh...  But a router is a Layer 3 function.    Having a router function won't make your switch any faster!

     

    You have components in the device that are for routing, and other parts that are for switching.  They may reside in the same chassis, but the functionality is still separated.

     

    Your FIB cache (CEF?) is just a method of making interaction faster.  However they are still separate!

     

    Kinda like if you go to Germany, you'll find busses, trucks and even garbage trucks that are made by Mercedes....   However, they don't perform like the gullwing does, no matter how you look at it!  

     

    Scott

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  • bavautoM3 12 posts since
    Mar 24, 2010

    Arul,

     

    Routing did not come to the switch to make it faster. It is a separate functionality all together. Switching frames is not the same as switching packets(movement of data units may be the same though). Packet switching occurs when the destination network does not exist on the same network segment as the originating network. It must be routed, recursed down to the exit interface.

     

    Also, On the contrary, do you know of any switch that switches at 10GB? I don't thinkEthernet switches are at 10GB. However, there are Core Switches that do operate at 10GB speeds. The Internet backbone for example. Perhaps 40GB by now, I don't know I don't work at that level yet. but the point is....you compared switches to a ferrari and a router to a dump truck..

     

    A heavy duty router is considered to be like a ferarri, switch network packets as fast as possible.let me repeat that.....As fast as possible, thats why you wont see policies, ACL's, rules, etc in place to slow things down. Its a kick *** high speed router that is designed to do one thing. Did I mention, its supposed to switch packets as fast as possible. A Catalyst 4500/6500/7000-Nexus switch is designed for this. Yes its a multilayer switch, but it certainly moves packets from one network to the next as fast as MF possibe. THATS ROUTING!!!!

     

    btw...I used to get confused by the term switching and routing. Switching is the act of moving data from one interface to the next. Routing moves data from one network to the next. you can SWITCH data packets from one layer 3 interface to another layer 3 interface. confused yet

     

    -MW

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  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,426 posts since
    Oct 7, 2008

    There are switches that work just fine at those higher speeds...   Some of them, however, are not produced by Cisco and may not be the best to talk about here!   But they're still switches based on their function.

     

    Even the Nexus, which are quite cool, are BASED on the ideas at Layer 2.  Does that mean there won't be other assistance given?  Now, the Nexus has integrated a lot of things into this concept of a "fabric"....   But all you're doing is distributing (or not) your decision making process.   You will be assimilated.  Resistance is futile.

     

    wink.gif

     

    Scott

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  • jk 2 posts since
    Apr 14, 2011

    Hi there Scott,

    Is there a significant differences between layer 3 switches with and without application-specific integrated circuit (ASIC)????

     

    jk

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  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,426 posts since
    Oct 7, 2008

    Sure.  Those without are significantly slower. 

     

    You process the same information.  You either have some hardware (ASIC) to help you out or you do it all in memory/software!

     

    Scott

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  • jk 2 posts since
    Apr 14, 2011

    Thx answering my question scott.

    Would you mind giving me some resources to show the differences between layer 3 switches with and without application-specific integrated circuit (ASIC)?

    TQ

    jk

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