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I have a mixture of fast ethernet (100Mbs) devices and gigabit devices. Despite that the PC is gigabit ethernet enabled, it syncs at 100Mbs only. However, my PC is syncing at gigabit ethernet speeds. Why? The router is a Netgear 3500WL. All cabling is gigabit ethernet capable cat 5E cable.

Correct me if I am wrong, the PC syncs at the slowest speed so it will sync at 100Mbs but communication between any two gigabit ethernet devices will take place at full speed? If so why does the PC in my room sync at gigabit speeds?

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It is difficult to distinquish one PC from another in this description. Could you edit and have a go at clarifying? – Paul Dec 19 '11 at 13:21
Clarification would be nice. In "If so why does the PC in my room sync at gigabit speeds?" is this between a gigabit or a 100MBS device? – ekaj Dec 19 '11 at 13:29
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2 Answers

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There are a few possible reasons:

1) The PC is not plugged into a gigabit-capable port or the port has been configured not to support gigabit speeds (unlikely in your case).

2) The network interface is not actually a gigabit interface or is configured not to negotiate gigabit speeds.

3) The cable is not wired correctly for gigabit. Gigabit requires all four pairs to be connected, not just the two needed for fast Ethernet. It is also much more picky about the pairs being wired correctly -- with each logical Ethernet pair being on a physical wire pair.

4) Some component is defective, damaged, or does not meet the appropriate specifications. Most commonly, it's the cable.

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I have mine wired to the B standard i.e. w/orange,orange,whitegreen,blue, whiteblue, green, white brown, brown for the RJ45 plug. I'll check the socket now. It's labelled as to which pair goes where. – ageis23 Dec 19 '11 at 19:14
Look closely at the ends to make sure all wires are making contact. If possible, try with another cable. – David Schwartz Dec 19 '11 at 23:38
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Small adds to David's answer

  1. When you have heterogeneous connectivity (i.e switch have both 100M and 1000M links active), max speed of every (Gb-type) link decrease to some extent from theoretical max value
  2. Even all OK as channel level (and as david wrote, you must verify it - and see both sides at least negotiated at Gb speed), there are some additional overhead on transport and application layer, which lower final speed also

I didn't see in your question:

  • results of pure-bandwidth tests between nodes (IPerf, NetIO)
  • Which protocol (or application) is used for syncing between (which OS?) hosts
  • Are firewalls, anivirus and other real-time monitor have place in process

Just to node: while I have near ideal Gigabit-LAN (according to NetIO results, 117-119MB/s, ~95% of max value), it's results for ftp-transfers permanently drive me nuts: 8.7-10.7MB/s for "most popular" direction, 2 (two, not two thousands) KB/s in one "bad", 32-45MB/s with FTPS on the "best"

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Actually I think the culprit might be a badly crimped RJ45. I have these connectors from maplin they have a cable guide with holes in it. For some reason everytime I try crimping the contacts slip and end up push away from the wire. So it looks like it's completely missed at least one of the 8 wires. what am I doing wrong? I must admit it's a cheapo crimper am using. I can't afford a proper professional one. – ageis23 Dec 20 '11 at 13:30
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