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> -----Original Message-----
> From: Gary flynn [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, October 24, 2000 3:08 PM
>
> Frank Knobbe wrote:
> >
> > The loopback on the LAN side causes the switch to
> > receive all packets it sends out. That triggers some switches
> > into behaving like a hub. Use at your own risk.
>
> Now that is interesting. I wonder which of two scenarios is
> occurring:
>
> 1) Broadcast packets are forwarded and thus read back through the
> same port. This registers that port in the MAC table for all
> MAC addresses that send broadcast traffic. Hence, you wouldn't
> see traffic for MACs that don't send broadcast traffic (few
> and far between, eh?) and you might lose the ability to see
> traffic after a timeout following a broadcast flushes the MAC
> from the table.
Could be. But I can see traffic pretty quickly, so there is no
waiting period to wait for broadcast packets form certain machines.
When I first noticed this effect, the first packet I saw was between
two other machines.
> 2) Regurgitating all the MAC addresses from the broadcasts fills
> up the MAC table or the switch simply can't handle the same
> MAC on multiple ports...either way in resulting in the whole
> switch turning into a hub.
> Can you sniff packets on other ports using a normal cable when this
> turnaround cable is installed?
That's something I have not checked (if the whole switch acts as a
hub, or only that port. I'll try it later and let you know.
Also, I haven't tested this with a lot of switches. Two worked, on
other occasions I connected to hubs. I encountered one hub where the
cable did not work (probably didn't get a link on the hub port), but
I did not investigate this further since I just hooked a regular
cable up to finish the investigation (same LAN/WAN problem). It would
be interesting to know how many switches can be hub-erized with
this...
Later,
Frank
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