L3 switches-> Efficient bandwidth utilization, for Campus network

Discussion in 'Cisco' started by qazmlp1209@rediffmail.com, Apr 19, 2007.

  1. Guest

    Cisco documents mention that the usage of L3 switches for the Campus
    network designs result in more efficient bandwidth utilization
    compared to using the L2 switches. Can anybody elaborate on why it is
    so?
    , Apr 19, 2007
    #1
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  2. stephen Guest

    <> wrote in message
    news:...
    > Cisco documents mention that the usage of L3 switches for the Campus
    > network designs result in more efficient bandwidth utilization
    > compared to using the L2 switches. Can anybody elaborate on why it is
    > so?


    this should be in the same set of white papers - try the reference designs
    at
    www.cisco.com/go/srnd

    it probably only matters if there is resilience, where the issue is about
    making use of redundant links when you dont have a fault.

    A layer 2 campus with resilience needs to use spanning tree to prevent
    active loops - and any blocked port isnt carry traffic.

    frankly i think this is probably a red herring, since bandwidth efficiency
    in a campus isnt that important - more ports in the core, high speed links
    and extra fibre are all typically fairly cheap anyway compared to overall
    build cost.

    much bigger issues are reliability and convergence time. once you are
    carrying traffic that doesnt tolerate long interruptions in forwarding (IP
    Telephony for example) then L3 is difficult to do without.
    >

    --
    Regards

    - replace xyz with ntl
    stephen, Apr 19, 2007
    #2
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  3. Scooby Guest

    <> wrote in message
    news:...
    > Cisco documents mention that the usage of L3 switches for the Campus
    > network designs result in more efficient bandwidth utilization
    > compared to using the L2 switches. Can anybody elaborate on why it is
    > so?
    >


    Well, I'm not exactly sure the reference that you are speaking of, but here
    are my thoughts...

    Many campus networks now have a need for a lot of different vlans and there
    is a need to route between the vlans. You can develop an L2 scheme with
    everything going back to the core to be routed. However, it would be much
    more efficient to have distributed routing at the campus. Given that campus
    networks now have high bandwidth usage, this could prove to be an extremely
    expensive using routers. However, L3 switches can be much less expensive,
    have many more ports and can forward the packets at a higher rate. So, it
    only makes sense to deploy a handful of L3 switches instead of routing
    everything back to the core or using multiple routers.

    Hope that helps,

    Jim
    Scooby, Apr 19, 2007
    #3
  4. Trendkill Guest

    On Apr 19, 8:45 am, "Scooby" <> wrote:
    > <> wrote in message
    >
    > news:...
    >
    > > Cisco documents mention that the usage of L3 switches for the Campus
    > > network designs result in more efficient bandwidth utilization
    > > compared to using the L2 switches. Can anybody elaborate on why it is
    > > so?

    >
    > Well, I'm not exactly sure the reference that you are speaking of, but here
    > are my thoughts...
    >
    > Many campus networks now have a need for a lot of different vlans and there
    > is a need to route between the vlans. You can develop an L2 scheme with
    > everything going back to the core to be routed. However, it would be much
    > more efficient to have distributed routing at the campus. Given that campus
    > networks now have high bandwidth usage, this could prove to be an extremely
    > expensive using routers. However, L3 switches can be much less expensive,
    > have many more ports and can forward the packets at a higher rate. So, it
    > only makes sense to deploy a handful of L3 switches instead of routing
    > everything back to the core or using multiple routers.
    >
    > Hope that helps,
    >
    > Jim


    I agree with Jim. Distributed layer 3 can be very rewarding, and is
    also the latest push from Cisco for campus datacenter networking.
    That being said, things get complicated in that distributed layer 3
    networks require some GREAT IP/Network planning, as you really need to
    focus on summarization. In the core model, you can create large vlans
    and trunk them out and slowly fill them up as servers are added. In
    the case of distributed layer 3 (or at least true, fully distributed
    layer 3), each subnet can only have as many IPs as there are ports.
    Not only that, but I'm sure you are going to end up with requirements
    for servers, or load balancing, etc, that will require segmentation.
    So how do you decide what your model for VLANs are going to be on the
    l3 switches?

    Perhaps a good medium solution is to roll out Layer 3 to each
    building, but still have a set of 'core' switches in each location
    that hold your layer 3. This way each building will have layer 3 and
    routing relationships, but you don't have to worry about potential
    segmentation nightmares. In short, there are 100 ways this stuff can
    be done, but it all comes down to your current requirements, your
    knowledge/understanding of changing/future requirements, and your
    budget. Pushing cores to each building may be costly, but then again
    you can use cores as distribution and access layer switches if you
    don't have ungodly requirements for bandwidth.

    This is why it is hard to find any kind of bible for 'network design',
    because there is no single right answer, and just about every business
    has vastly different requirements.....there are always exceptions.
    Trendkill, Apr 19, 2007
    #4
  5. Scooby Guest

    "Trendkill" <> wrote in message
    news:...
    > On Apr 19, 8:45 am, "Scooby" <> wrote:
    >> <> wrote in message
    >>
    >> news:...


    <snip>

    >
    > This is why it is hard to find any kind of bible for 'network design',
    > because there is no single right answer, and just about every business
    > has vastly different requirements.....there are always exceptions.
    >


    That's why we get paid the big bucks, right? :p
    Scooby, Apr 19, 2007
    #5
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