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mrisher
Asked: 2011-09-06 21:00:49 +0800 CST

How can I troubleshoot APIPA (169.254.x.x) in physical network cabling?

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all: We have just started using an existing Cat5e cable to run 100Base-T to a new office, but unfortunately, machines in the new office see link but receive an APIPA address (169.254.x.x).

I brought the same computer into the network closet and plugged it directly into the hub and everything works okay, so it must be the wiring through the walls.

Can I use Wireshark or some other (Mac) software to confirm this? Or is there an inexpensive hardware test, short of pulling the cable back through the walls?

Thank you, /m

networking ethernet cable cat5e

2 Answers

  1. Best Answer

    There are two main tests for Ethernet Cable:

    • Continuity Testing. This checks that all pairs are connected in the correct order and that there is a continuous signal from one end of the cable to the other. You can buy these testers for peanuts: http://en.wikipedia.org/wiki/Continuity_tester

    • Cat5e Cable Analysers. These testers cost upwards of AU$1k and they test the exact electrical conductivity, interference etc of the cable and let you know if it falls in line with Cat5 specs. Assuming the cable is good, and the jacks are fine (check with the continuity tester), this device will tell you if there is too much interference or signal loss which can happen when: The cable gets old, something wears/eats away the shielding, the cable is coiled tighter than regulations, the cable runs parallel to power cables etc. http://www.flukenetworks.com/datacom-cabling/copper-testing/dtx-cableanalyzer-series

    You can hire these testers, but it can be expensive. It'll be cheaper than re-cabling your whole office.

    Don't forget that there are Ethernet Specifications which dictate how long your runs can be, how many hubs/switches etc. AFAIK a hub means that both cables plugged into the hub need to be shorter than the Ethernet Max Length, where as a switch stores and forwards the packet, so perhaps you can get the max length on both sides of the switch. With the prices of switches, there's never any reason to use a hub.

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  2. You will probably get more "mileage" with a wiring test set to ensure there are no physical issues with the cabling (mis-match of pairs, length tolerance, physical damage, etc.).

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