RE: The devil's in the details

["Thomas Crowe" <thomas.crowe () bellsouth net>]

 Matt;

Almost all medium to high end switches that I have delt with have the
facility to set up a span port (thats a cico term) for doing very much what
you just said, sniffers and such.  These switches can usually be configured
and send / recieve or recieve only.

> My problem is that a couple of my networks involve switches,
> which, as part
> of the new and improved security policy, will involve VLANs.
>
> I could throw the IDS on a hub with the firewall and connect that to the
> switch, but that doesn't do anything for internal threats (which are what
> is necessitating the VLANs.)
>
> Has anyone figured out a good way to set something like this up? Ideally,
> some switch manufacturer would have thought of this ahead of
> time, and made
> a port on the switch that dumped all the packets, but then you're dealing
> with packet loss unless that one port is significantly faster
> than the rest
> of the switch.

The possibility exists for packet loss primiarly in chasis based switches
that use different media types ie FDDI, 100BaseTx, 1000BaseFx, etc....  Then
you could be losing packets due to either to the switch engine not being
able to handle packets per minute (ppm's) or the switch not being able to
keep up with the layer 1/2 conversion.

> I could try to figure out some policy based configuration,
> but I don't want to go buy a gigabit plane for each of my switches, and it
> doesn't sit right with me to depend on the switch management elements for
> the completeness of my security data.

Another consideration in general about switches, is to always get
'non-blocking' switches that way any packets that the switch processor can't
keep up with simply gets flooded to all ports.

> Any responses would be appreciated.
>
> -Matt

Thomas Crowe
Production Network Systems Administrator