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198060 Views 29 Replies Latest reply: Feb 20, 2012 2:40 PM by Michael Strasner RSS 1 2 Previous Next

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Router Vs Layer 3 Switch...

Feb 1, 2010 11:22 PM

ExceptionalBoy 128 posts since
Jun 30, 2009

Hi all...

 

As we all know that Layer 3 switch can perform the routing tasks if routing is enabled.But I`ve some questions regrading this :

 

1. What is the main difference between this two?

 

2.What is the choosing criteria between this two i.e. when should I use which one?what`s about the cost effects?

 

3.Why router is needed if there is existence of Layer 3 Switch?

 

Thanks for your time.

 

Take care.

 

Regards,

Jahid

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    1. Feb 2, 2010 12:05 AM (in response to ExceptionalBoy)
    Re: Router Vs Layer 3 Switch...

    Hi Jared

     

    L3 switches do not have WAN interfaces.

     

    You can connect Ethernet circuits to a switch so you only need a router if you want to connect traditional circuits such as E1 E1 SDH or old technology such as X21 V35 or async circuits.

     

    As far as I know Call Manager Express does not run on a switch but does on a router.

     

    Switches support WiFi controller, Firewall so are quite powerfull.

     

    So you need to understand the business requirement before deciding router or switch.

     

    Also routers can include switch modules.

     

    Regards Conwyn

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,396 posts since
    Oct 7, 2008
    Currently Being Moderated
    2. Feb 2, 2010 7:54 AM (in response to ExceptionalBoy)
    Re: Router Vs Layer 3 Switch...

    If it routes, it's a router.  

     

    L3-switch is a marketing term.  It's a router with only ethernet interfaces and lots of them.  It also has a switching function to it.  Which makes it both a router and a switch!

     

    The differences will vary based on model.  It depends...  Cost varies as well, everywhere from inexpensive to very expensive!

     

    And truly there isn't a "need".  You need an L3 device of some sort to exit your subnet.  how you design that, or what specific piece you use is entierly up to you.

     

    Scott

  • Jared 5,501 posts since
    Jul 27, 2008

    Scott & Conwyn have both made good points here.  They are both right.  Traditionally, Routers were devices that connected the LAN to the WAN and switches were just LAN devices and you may add a layer 3 switch to the lan if you had some vlans and didn't want to use a router.

     

    However, as technology changes, the tradition of the WAN and LAN is fading.  My "WAN" links are actually 1 gig single mode fiber circuits that terminate to an ethernet fiber interface on a Layer 3 switch, a 6500, 4500, 3750 or even a 3560.  Now some will say that I have a MAN with those kinds of links.  It seems that as Scott said, Cisco Marketing is still stuck on calling a router a device that terminates a traditional WAN link,  I do agree that if the device routes, it is a router.... to some degree.

     

    One thing I did notice regarding routers and layer 3 switches, and I will admit that router model and IOS version may play very heavily into this, and that is Routers seem to support more traffic monitoring features, such as netflow and nbar where as Layer 3 switches don't seem to have that kind of support.... until you get to the 6500.

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    5. Feb 4, 2010 12:41 AM (in response to ExceptionalBoy)
    Re: Router Vs Layer 3 Switch...

    Hi Jahid

     

    My apologies. I think CLN should put the person's name in the reply title so you could see the corrrect spelling instantly.

     

    Regards Conwyn

  • Mohamed Sobair 340 posts since
    Oct 21, 2008
    Currently Being Moderated
    6. Feb 4, 2010 1:05 AM (in response to ExceptionalBoy)
    Re: Router Vs Layer 3 Switch...

    Hi,

     

    Technically, the differences are:

     

    1- L3 Switch do switching at layer 3 by preserving the source and destination mac and preserving the TTL value of the IP header of the 1st routed packet, so the first packet is routed using normal routing lookup, but after that all packet are switched.

     

    2- router do normal routing lookup, but by introducing fast switching and CEF, packets are also now switched on a router.

     

    3- Switches doesnt support some QoS features.

     

    4- Switches doesnt support NAT.

     

    5- The forwarding on switches is done on ASIC (Application Specific Integrated Circuits) which is done in hardware rather than a software.

     

    6- Forwarding on routers are done in a software.

     

    7- router supports different WAN technologies (modules) unlike switches.

     

     

     

    HTH

    Mohamed

  • ChadB 4 posts since
    Jun 2, 2009
    Currently Being Moderated
    9. Mar 29, 2011 4:27 AM (in response to ExceptionalBoy)
    Re: Router Vs Layer 3 Switch...

    I was just thinking about this.  I didn't learn about Layer 3 switches until the bcmsn.  I know in CCNA they were still really pushing the router vs switch concept.  Talk about throwing a monkey wrench into things when you throw in the concept of Layer 3 switch.

     

    So to review:

    1. A pure router will do just that, typically no switch ports, in todays cisco world I don't even know if they make one of these, wouldn't that be something like an ASA with 1 or (2) 100 mb or gig ports with a serial port or similiar?

    2.  A switch will just allow connections to edge devices, a true layer 2 switch like a 2960, Int vlan's is what allows management of the switch at layer 3.  No routing between vlans, this is where router on a stick comes into play.

    3.  A layer 3 switch integrates both abilities, but it depends on the model on how integrated and featurific it is.  Will it support netflow?  Will it route between vlans?  If you do a show ip route what will be displayed?  How does it implement vlans, is it traditional vlan.dat file or will it do the switching way with show vlan?

    -- The simplest true layer 3 switch will support all switching features, but have the ability to do routed ports and route between the vlans.  I have had a Integrated services router like a 1760 or 3725 or similiar where they had a small switch module, say 4-24 (100).

    The definition of a layer 3 switch also may include the ability for a port to be either a routed port or a switched port, the commands switchport vs no switchport followed by having to assign it an ip address.

     

    This is another point that also took some getting used to.  In a port that can be either layer 2 or layer 3,  or strictly layer 3 or layer 2.    Example, a router can only do layer 3, so to do inter vlan routing  while connecting to another switch via  trunk port you have to give it sub interfaces to a physical switch port, give each one its own ip address and tag it with the encapsulation dot1q #.  Router on a stick,  vs switchport mode trunk command with layer 3 interfaces via the "int vlan 1" with an ip address assignment.

     

    While I understand the ccna approach to teaching funamentals and where thing started, it no doubts confuses someone especially whena  questino asks about the differences between a hub/switch/router.  In todays world, hubs don't really exist, and in a large company odds are your going to be using a layer 3 switch.

  • Steven Williams 3,266 posts since
    Jan 26, 2009
    Currently Being Moderated
    10. Mar 29, 2011 5:33 AM (in response to ChadB)
    Re: Router Vs Layer 3 Switch...

    Switches = many more ports!

  • samarjitdutta 56 posts since
    Jan 6, 2010
    Currently Being Moderated
    11. Apr 13, 2011 6:23 AM (in response to ExceptionalBoy)
    Re: Router Vs Layer 3 Switch...

    let us think about the simple senario//

     

    multiple vlan with intervlan routing.

    what will u use for inter vlan routing.......... L3 switch or  ROUTER.

    if you are using router the trunk connecting the switch will get overload due tok bandwith limitation.

    But if u are using L3 switch this problem will not be a problem.

     

    but every think depends on senario, technology required, required interface

  • TheOtherTomJones, CCNA, CCDA, CCNAS 317 posts since
    Sep 6, 2009
    Currently Being Moderated
    12. Apr 13, 2011 7:26 AM (in response to ExceptionalBoy)
    Re: Router Vs Layer 3 Switch...

    Keep in mind that the backplane of some L3 switches may be faster than some models of routers.

     

    A 3750X for example has a faster backplane than a 2900 router. However routers will support far more media types than most switches (exclusing 6500's). The actual hardware design of some switches may or may not be more beneficial for their use in certain circumstances - the 3750 model switches are actually designed to be oversubscribed where as certain model routers are not.

     

    In fact, when I think about it more deeply, the only significant difference is between access layer routers and switches. Once you get to distribution and core routers and switches, there seems to be little difference... other than cost 

  • oliver-learning net 82 posts since
    Nov 5, 2008
    Currently Being Moderated
    13. Apr 21, 2011 12:00 PM (in response to ExceptionalBoy)
    Re: Router Vs Layer 3 Switch...

    I've read the replies here but still have my own very similar questions,...

     

    Okay so a router is L3 and switch can be L3 and they are essentially doing the same thing bar obvious  quite big technical differences across models etc. But my question is how L3 is implemented is this not substantially different , in short:

     

    Does a L3 switch implement a routing protocol ? Am I just being stupid or is this where there is some considerable differentation between a router and a L3 switch its routing implementation? I strongly suspect this is categorically different between a switch and a router, am I right in any way?

  • Steven Williams 3,266 posts since
    Jan 26, 2009
    Currently Being Moderated
    14. Apr 21, 2011 12:30 PM (in response to oliver-learning net)
    Re: Router Vs Layer 3 Switch...

    Depending on the IOS version the L3 switch is running, yes it can run a routing protocol. Router vs. Switch....this whole thread states the differences. It all depends on your design and what you are trying to accomplish. Do you have only a layer 2 network and now have the need for inter-vlan routing? Then a simple  router running router on a stick can accomplish your goals with minimal changes on the network. But then again all my "routers" are 3560's because L3 switches are about the same price as a router if not cheaper and getting more port capacity for my money. I use routers for site to site vpn connections and voice gateways. Like I said though depends on your design goals and currect design and what you want to accomplish.

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