ANNOUNCEMENT: Live Wireshark University & Allegro Packets online APAC Wireshark Training Session
April 17th, 2024 | 14:30-16:00 SGT (UTC+8) | Online

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

From: Hansang Bae <for_list_hbae@xxxxxxxxxx>
Date: Tue, 14 Jul 2009 13:15:59 -0400
mv652@xxxxxxxxxxxx wrote:

Hi,
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.


As Sake pointed out, binary files are easier for folks to digest and offer help. But there's only a small chance that your trace file will show anything significant.

Besides what others wrote already, make sure you routers arp and switches cam timers are set identically. Cisco's router default and Cisco's tcam timers are different by default. And it can lead to flooding of unicast packets.

Also, if you have the typical U design (two routers at top, connected to two switches on the bottom, the two switches connected together to form a U), the flow of packets can confuse the switch and cause unicast flooding.

You should a) post a binary trace of your problem and b) share your topology with a a bit more detail if required.

--

Thanks,
Hansang