Re: unswitched behavior of a switched network...

[Krugger <merc4krugger () gmail com>]

On 10/13/06, Jon Hart <jhart () spoofed org> wrote:
> Greetings,
>
> I've got a situation here that I can't quite figure out.  It is well
> known that it is possible to cause a switched network to act like an
> unswitched network by flooding the CAM table.  There are countless tools
> and documents out there that cover the offensive and defensive measures
> related to this issue.
>
> While this isn't Cisco's official documentation on this issue,
> http://xrl.us/r8k7 says:
>
>    "Content-addressable memory (CAM) overflow: A CAM table is used to
>    determine where to direct incoming frames depending on which port the
>    incoming MAC address came from. When the CAM receives a frame with an
>    unknown destination, the proper procedure is to flood frames within
>    the acceptable Layer 2 domain (the proper VLAN). Hardware and
>    software tools are available (some for free), that can flood a switch
>    with MAC addresses. Once the CAM table limit is exceeded, switches
>    behave differently depending on the brand of the switch."
>
> My question is, has anyone seen a situation where the same broadcast
> behavior occurs, but the CAM table itself is not overloaded and there is
> no good reason for entries to be expiring?  Furthermore, even if the
> entries were expired, has anyone encountered situations (malicious or
> otherwise), where a given port will receive traffic outside of its own
> L2?
>
> Thanks,
>
> -jon

Some router have an option of dumping all traffic to a give port, so
if you are connected to the right router port you will see everything
as if it was a hub. At least I already saw a router configured that
way, that port that was connected to a computer that was dedicated to
run snort.

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