DHCP works on short but not long cable question:

[NEXSENJ]

I have a baffling problem I hope someone has a solution to:

My setup: cable model to Apple Air port router.

When I plug my Macbook into the Air Port router ethernet port via a short 3 foot Cat6 cable it works fine: Comes up with IP 10.0.1.13 and has Internet access.

When I plug the same laptop to the same router port via a longer Cat6 cable it doesn't work:

It returns IP 169.254.246.97 and the laptop says: Ethernet has a self assigned IP address" and NO internet connectivity.

I have tried 4 different long cables all of which have been tested with a cable tester for continuity and pin assignments (straight through). All cables were installed at the same time and are probably 100 to 125 feet long but far less than the 300 foot (100 meter) recommended limit.

And here's the real clincher: One of them has been working fine and connects a Tivo to the Internet for updates as well as streaming Netflix and Amazon video with NO hiccups so I "know" it connects to the Internet from the TIVO.

So, why can't my Macbook connect over the longer cables (like the TIVO does) and why is it coming up with a different self assigned IP address when connected via the longer cables?

 

[kanewolf]

Do the long cables follow the TIA 568B color code? If not then they probably have too much noise and crosstalk. The order that the wires are in an RJ45 is important and a cable tester that only shows continuity and straight through won't show that the wires are properly paired.