Ethernet cable too long?

I have an Ethernet cable running from a Huawei ADSL router to a computer> The total length is 61 meters (200 ft).
When connected to the computer, a cycle of identifying, disconnected, identifying, disconnected keeps looping with a second interval in between. A shorter, 2 meter cable works just fine. I checked the wiring (T568B) and it's OK. The cable looks physically OK too.
Is the length of that cable causing this?

Solution 1:

It's not the length (100 meters -approximately 330 feet- is the max for ethernet UTP), but most likely the quality of the cable is bad. Maybe the cable is damaged internally or at some point was pinched severely. This is not always visible from the outside. Could also be that one or both ot the RJ45 connectors is crimped on badly or is incorrectly wired. (The cable should be 8 wires 1 on 1 and the ordering of the colored wires IS important.)

EDIT: Some clarification regarding cable categories: For normal ethernet over UTP cable:

• CAT5 cable: 10 & 100 Mb/s over 100 meters.
• CAT5e cable: 10 & 100 Mb/s over 100 meters, upto 10 to 30 meters for 1 Gb/s, depending on cable quality.
  (Officially CAT5E does Gigabit over the full 100 meters, but in practice this is very rare. Most cable is not of good enough quality. Signal usually degrades to 400 Mb/s or 200 Mb/s)
• CAT6, 6a and 7 cable: 100 meters for 10/100 Mb/s and for 1 Gb/s.
  10 Gb/s is also possible: For Cat6 upto 30 meters (again: may vary depending on quality of cable).
  Cat6a & 7 are rated for the full 100 meters with 10 Gb/s.

Solution 2:

I have had a cable of 30M be faulty, and a cable tester (albeit a cheap one) showed it as OK / didn't detect a fault.

It may be that longer cables can be trodden on and that makes them less reliable(by damaging them).

The kind of ethernet cables that I find to be reliable, have been one with a rugged jacket, they are expensive, and maybe a better quality build too.

I used to get cables from a company that specialised in cables, but I just found them bad quality! But when I got a few rugged cables (and it would have been a specialist company making them), I found those were very reliable. So, maybe as a rule of thumb to get a quality cable, you could look for rugged jacket ones from a company that makes the rugged jacket ones, if you're willing to pay the price for such cables.

Solution 3:

It could be that you are using an incorrect category cable. You didn't mention what speed you are using. Here is a link to Cisco's explanation of cable types. At a minimum you should be using CAT 5 cable, this gives minimum error rate for 100BT and lower. With Gig-E widely available, CAT 6 cable is needed for the length run you state.

http://www.ciscopress.com/articles/article.asp?p=31276

Solution 4:

Well, since no one has mentioned it...

There is no reason to believe that a particular NIC's line drivers will actually push electrons all the way out to the Standards's maximum lengths. I have had exactly the problem you describe fixed by replacing one instance of a NIC with another instance of the same NIC -- same part number, same lot. I've also found that some NIC models just cannot push signal the full length of a perfectly good maximal cable. Discovering this can be done with an oscilloscope and some messing about.

Remember: the standards only promise maximum lengths. Cheap card manufacturers are not obligated to reach those maxima.