In Wireshark Network Analysis, Chapter 3 mentions half-duplex and full-duplex networks (and traffic). How can I determine which type of network I'm on? asked 30 Nov '10, 17:38  sutch |
One Answer:
You can't really tell. If you hard code a switch port side (or the NIC side), it will not send any link pulses used by auto negotiation. However, if you hard code both sides (switch and the NIC), you will be running in FD network. So absence of link pulses is not enough to determine what type of network you are on. In modern day networks, the vast majority of devices are running in FD mode. Not that HD was all that much slower than FD, but with switching being a commodity technology, almost no one runs in HD mode. Exceptions to the FD rule include older printers, some industrial and vertical appliances. But the vast majority of today's network is running FD. answered 30 Nov '10, 19:46  hansangb |
This is true for 10/100 MBit networks using the 802.3u standard of negotiating HD/FD. Gigabit networks have a new standard (802.3z), where link pulses are sent even when the card is hard coded to avoid HD/FD mismatch errors. Correct me if I'm wrong :-)
Off the top of my head, I don't recall if FLPs are sent in hard coded Gig world or not. But it's a moot point because there is no half duplex Gig. It's in the standard, but no manufacturer created nor sold a half duplex PHY. The idea of having to support carrier extensions etc probably scared them off! :)
I just wish I could go back in time and implore the 802.3 folks to make the "fallback" be FD. At the time it made sense to specify 100/HD as the "safe fallback" but nowadays, it's just damn annoying!!! It causes so many duplex mismatches.
Going back in time should be added to Wireshark v 1.6! <g>