Re: [fw-wiz] Vlan's as effective security measures?

From: Todd Joseph (
Date: 02/13/04

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    To: Brian Ford <>
    Date: Thu, 12 Feb 2004 18:26:50 -0500

    The Cisco bug DB has plenty of entries for switches with "bleeding
    VLAN" woes. Carefull driving your own car. :)

    VLANs are a cheap/convenient way of defining subnets and moving ports
    logically. A separate switch (or switches) for each subnet is a clear
    win over VLANs -- it just costs more (in hardware and cable/port

    Fortunately, there's still lots of cheap Cisco (and other) gear on
    Ebay - making it more $$ effective than some realize.

    >And cars crash and cars burn and people are dying in cars all the
    >time. And cars can be made to carry disease and explosives and kill many
    >people with just one car and driver! So let's all abandon our cars and
    >start walking to work every morning. If we're late the boss will
    >understand because cars are dangerous. ;-)
    >You should probably research the switch that you buy and use in order to
    >make sure that it doesn't do these things.
    >Your mileage may vary!
    >Liberty for All,
    >At 12:00 PM 2/10/2004 -0500, wrote
    >>Message: 4
    >>Date: Mon, 09 Feb 2004 12:52:31 -0800
    >>From: John Hall <>
    >>To: "Ware, Larry" <>
    >>Cc: "''"
    >>Subject: Re: [fw-wiz] Vlan's as effective security measures?
    >>1. A surprising number of network devices' VLAN implementations
    >> will leak packets between VLANs under heavy loads, or in some
    >> cases randomly all the time.
    >>2, Some switches have a single forwarding database which includes
    >> VLAN tags and a host presenting a carefully chosen MAC address
    >> can sometimes hijack traffic for a host on another VLAN.
    >>3. Some switches flood ARP requests across VLANs.
    >>4. Some switches flood all traffic under heavy load.
    >>5. Few switches and routers have adequate configuration security.
    >>Don't depend on VLANs to guarantee the separation of two networks
    >>that *must* be separated. Your security is only as good as the
    >>weakest element in your infrastructure and the security of most
    >>switches (and to a lesser extent routers) is pretty weak.
    >>Ware, Larry wrote:
    >> >Forgive a long out of field, and now working on getting back up to speed
    >> >firewall admin, but would someone care to educate me concerning the securit
    >> >issues related to VLAN's? I have lots of them, and need to know why a VLAN
    >> >is not an effective adjunct to firewall and router security policies.
    >> >-larry
    >> >
    >Brian Ford
    >Consulting Engineer, Security & Integrity Specialist
    >Office of Strategic Technology Planning
    >Cisco Systems Inc.
    >The opinions expressed in this message are those of the author and not
    >necessarily those of Cisco Systems, Inc..
    >This email address is transmitted from San Jose, California, U.S.A..
    >firewall-wizards mailing list
    firewall-wizards mailing list

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