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I am trying to connect two computers together using a Cat6 cable. Both computers have gigabit Ethernet cards, and the "Network" tab in Task Manager reports the link speed to be 1Gb/s for both. One computer is running Win7 x64, and the other is running Win8 x64. At the point of testing, both computers were disconnected from WiFi and were assigned static IP addresses 192.168.10.1 and 2.
Testing with iperf reports approximately 430Mb/s throughput, which is nowhere near the reported link speed of 1 Gb/s.
I've tried replacing the cable with a second, new, Cat6e cable, as well as a Cat5e cable, but the average throughput remains roughly (+/- 50Mb/s) the same.
I've tried going into Device Manager and changing "auto-negotiation" to "1.0 Gbps full duplex" on both computers. Not that it should make a difference, since both sides would have auto-negotiated to 1.0 Gbps anyway.
Is there something I'm missing out here?
Is the cat6e cable professional grade or homemade? and how long is it? – Tyson – 2014-07-26T17:17:39.823
2Have you enabled jumbo frames? – ChrisInEdmonton – 2014-07-26T17:30:36.330
1If the link speed is negotiated at 1 Gbps, and remains there, it is unlikely that there is a problem with the cable. For short runs, 1000BASE-T usually works over garbage cable it's not supposed to just fine. – tgies – 2014-07-26T18:12:58.353
@ChrisInEdmonton Even with standard 1500 Byte frames, TCP/IPv4 over gigabit Ethernet is 94% efficient (940+ Mbps). Jumbo 9000 Byte frames just let you squeeze another 4-5% out of the link. – Spiff – 2014-07-26T18:42:14.220
Louie, what TCP window size did iperf report? Just for giggles, force it huge by adding
-w 2M
to both iperf command lines. What chipsets do your gigabit Ethernet interfaces (NICs) use? I'm leaning toward an answer of "you just have crappy NICs". – Spiff – 2014-07-26T18:46:28.393@Tyson I'm not sure how to distinguish between "professional grade" and "homemade"... but anyway, the Cat5e and Cat6 cable were provided by my ISP during modem installation, while Cat6e was bought online. All three cables are 1-1.5m long, and none of them have any visible brand marking. (Is there actually supposed to be a visible brand logo printed on the cable?) – Louie Tan – 2014-07-27T08:35:44.927
@Spiff "Realtek PCIe GBE Family Controller" for both laptops. The NIC is marketed as Gigabit Ethernet though, so it would be quite a stretch for it to actually only be capable of handling less than half of said "gigabit Ethernet"... – Louie Tan – 2014-07-27T08:46:30.687
As an option - try to boot these computers with a live Linux distro (one at a time, then both) and perform tests again - this will show if your current operating system and/or drivers have any network related issues. If results will be the same - we know the hardware part needs to be handled. – VL-80 – 2014-07-27T13:16:56.067