Wireshark-users: Re: [Wireshark-users] TCP / SMB Broadcast?

From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Tue, 14 Jul 2009 01:38:37 -0700

On Jul 14, 2009, at 1:21 AM, mv652@xxxxxxxxxxxx wrote:

I'd appreciate if someone could take a look at the attached capture of 11 packets and explain why I am able to see the TCP & SMB negotiation between these two hosts. My capturing device has IP Address 10.0.4.26 connected on the same switch, same VLAN as the two systems in the capture (10.0.4.50 & 10.0.4.6). The capturing system's nic is in promiscious mode.

Note - I understand why I see the ARP request as it's a broadcast to the network address, what I don't understand is why I see the rest of the communication between the two. I even see an ICMP reply from one host to the other, but not the original request.

These systems are running on a managed switch, not a hub.

Perhaps the switch is, for some unknown reason, putting traffic sent from 10.0.4.50, or traffic sent to 10.0.4.6, onto the switch port into which the capturing machine is plugged, as well as the port into which the machine with MAC address 00:17:3f:0a:c5:3a (i.e., 10.0.4.6) - but not doing that with traffic going the other way.