Re: Measuring VLAN performance

Discussion in 'Cisco' started by Stephen, Jun 11, 2009.

  1. Stephen

    Stephen Guest

    On Mon, 8 Jun 2009 12:17:55 +0100, "Gerard Gallagher"
    <> wrote:

    >Hi all,
    >I'm in the process of converting a flat network (approx 2000 users) to a
    >more layered approach using VLANS.
    >We have 2x Cisco 6509 switches with Sup720's configured as a HSRP core,
    >linked with a l3 etherchannel, and an l2 etherchannel.

    i prefer to minimise the scope of VLANs, since most campus hassles
    seem to come down to misconfigured devices or L2 problems such as
    spanning tree loops.

    See if you can confine a spanning tree to an individual switch - ie
    the Cat 6509s have routed only interfaces, (or no VLAN connects to
    more than 1 physical port).

    Ideally spanning tree is there to protect against misconfig, but isnt
    actually needed in normal operation, as there are no L2 loops.

    Oh - and turn off VTP......

    there are some cisco docs about tweaking campus designs that may help

    >Each closet will comprise 3 vlans - one for voice, one for data and VLAN1
    >for management.

    VLAN1 carries a bunch of "wierd stuff" in cisco land - you might be
    better off with management access away from vlan 1 in a set of routed
    domains / subnets.

    It also pays to keep everything you can off VLAN1 since that is where
    an unconfigured device will put all its traffic - if VLAN 1 is not
    routed to servers etc the installer has to sort it out properly rather
    than walking away because it just works.

    >I would like to know how the addition of vlans is affecting the overall
    >network - i.e as areas come off vlan1 for user traffic and get moved to
    >their respective vlan how the overall network performance is hopefully
    >improving, and I'm looking for any information that would help me measure
    >this, or indeed any aspect of the network which I should be measuring. The
    >idea is to be able to show how the vlan introduction is helping the site.

    If you move all the "new config" traffic off VLAN 1 you can compare
    old and new at any point in the process.

    however, as with the other posters i would not expect major changes
    apart from broadcast reduction in normal operation - unless you use
    something that misbehaves with a flat network such as multicast.

    The major advantage with routing in the core is you get better fault
    isolation, and your campus gets more resistant to various kinds of
    degraded operation.

    The flip side is you need more planning, a good address plan, and the
    configs need to be consistent with the design on the core switches at
    a minimum.
    >Many thanks in advance.


    - replace xyz with ntl
    Stephen, Jun 11, 2009
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