ethernet tap

[g2c]

Hello,
I am trying to debug a client server problems I have with arduino and for that I'd need to analyse the communication packets to / from the Ethernet shield. I was thinking of a cable connected to my pc running wire shark.
could someone give me some guidance?
Many thank in advance

 

[geko]

If you can get hold of an old Ethernet hub (not a switch) all traffic appears on all ports. They're a bit hard to find now and only operate in half duplex. I used to keep an old 100Mb hub at work for troubleshooting with Ethereal (Wireshark). Now days any half decent managed Ethernet switch will let you mirror traffic to another port.

I doubt trying to physically tap the wire pair would even work, if it did you're only going to see half the conversation, i.e. The Tx data to Rx data in one direction. A full featured switch port mirror will mirror the tx and rx traffic on one port out of the mirror port so you see the whole 'conversation' in the Wireshark capture.

The alternative if you can do it, is to run Wireshark on one of the end devices, then it sees the tx\rx traffic and you don't need any taps or mirrors.

 

[g2c]

Thank you Geko,
I definitively agree about the disadvantage of a tap. Unfortunately i don't have a switch per se I do have dsl/cable routers which could be used as switchs with dhcp disabled but they do not offer port mirring. I think i could manage to have 2 ethernet port on a PC, Is it reasonable to think of a program which will forward between the ports and having wireshark capturing the data from/to one of the port?

 

[geko]

I believe if you have two NICs in a Windows PC you can configure them to bridge between networks. Never done it but I'm sure if you Google 'windows bridge' you'll be able to find out more. If you can bridge the traffic then monitoring one NIC with Wireshark you'll see the traffic passing between LAN segments.

 

[g2c]

You're right, seems straightforward under windows. I'll try it and report results here