Why do I have to set the "Speed and Duplex" setting to connect faster to my LAN?

Question

My LAN originally took about 3-5 minutes to achieve Internet connectivity. This was way too long for me, so I found this fix which basically said:

In advanced settings of network adapter, for "Speed and Duplex" I set "10 Mbps Full Duplex"

I set it to "100Mbps Full Duplex" (previously, it was set to "Auto") and now my adapter achieves Internet connectivity almost instantly.

My question is, why did this fix my problem? I'm just curious as to the internal working in this situation.

Solution

Your network cable is badly broken, most likely having the wires assigned to pairs incorrectly.

Just having both ends using the same assignment is not enough. Signal pairs must be assigned to wire pairs because wire pairs are twisted differently to reduce crosstalk. Mismatching will turn this against itself, causing each half of a signal pair to be twisted differently, and worsen crosstalk.

Do not ever force full duplex, it will cause huge problems. Fix the broken cable. Pick either 568A or 568B and ensure both sides are wired according to it.

Comments

[Anish Ramaswamy]

Okay this makes sense! Thanks! But, I have another laptop which does not have this problem (i.e. I don't have to force full duplex to connect fast). What does this mean now?

[David Schwartz]

@AnishRam It is perfectly consistent with the cable being marginal. Marginal hardware behaves unreliably.