Realtek/Buffalo DHCP problem or simply faulty cable?!

[alexuk]

This has had me tearing my hair out for weeks.

I have a duo with a realtek onboard that would work OK when connected to to a buffalo WHR-G54S or directly to VM's box. The house had a network cable going out, then into the left and back into the back room upstairs, trouble was one connector had been removed while plastering. I put in one female at that end and tried hooking it up but got no connection. This is not something I'd done before so I spent ages trying to make sure I lined up the ethernet wires correctly but all it appeared in order. Moved to the other connector upstairs (a male) and proceeded to put hook up a female there too (I had fems not males). The cable is now a patch cable (ie not a crossover).
Tried again, no result. Inspected the modem logs and could see the PC making DHCP calls and being offered IPs but not picking up offers. I tried fiddling with lots of things in the router but no result.

Not one to be discouraged so easily I tried running another long cable (this one the new one that comes with VM's self install) and the PC / onboard realtek would accept the request. PC runs Vista and Fedora Core 8 - both work.

The conclusion would be the house cable is broken somewhere. However if I hook up the laptop it actually works fine! So should I conclude the cable in the house suffers from signal degradation so badly that the PC cannot establish a connection (but a laptop can!)? I took care to cross the wires just at the very end but again that's not something I've ever done before. But even if so why do I see the correct DHCP requests in the logs? The realtek inbuilt BIOS tests reports the lan (when connected through the house cable) as being 100Mbit with a length of 28m: if the degradation was really bad should I not expect to get a read of >100m?

Obviously the solution is to run the PC upstairs with no wires but given all the time I've invested on this any help would be greatly appreciated!

[flowrebmit]

The house network cable should not be crossed over at all. The only time that you should normally be using an X-over cable is if you are connecting two computers directly together (i.e. without a switch).

Your laptop probably works because it has an auto X-over detection and can un-X-over your X-over house wiring.

Your explanation is a bit hard to follow, so I await to be proven wrong as a clearer picture emerges:)

[flashpaul]

The reason the cable works with the laptop is that the laptop can auto detect the cable type and it then does not matter if its a straight or crossed cable

The PC either cannot auto detect the cable type or this facilty is not enabled (look for Auto MDI in the settings)

There may be a termination issue so its worth checking that your external cable is identical to the internal one

Finally another option would be to purchase an ethernet switch

http://www.cclonline.com/product-info.asp?product_id=10522&category_id=152&manufacturer_id=0

They arent expensive and will resolve the patch/crossover issue and clean up the signal

[alexuk]

Thanks for your help!!

As far as my understanding goes the cable I put in is NOT crossed over right now - I do not know whether it was or not originally as one end went together with the plastering. :)
The reason I say this is that the patch Fem-Fem patch cable I built has the same ending on both connectors. The two Male-Male cables I am using to connect it to the router and the PC are patch cables with same endings so I presume the overall result is a patch cable. Is that correct?

Having said I'll check any BIOS setting for AutoMDI (didn't see any last time I checked). PC does not work in Vista nor Linux but I'll try to see if Vista has a switch to that effect.

Would definitely buy a switch if this would solve the problem - I am bit hesitant as it adds another box/PSW to the system. Obviously I could also put in a wireless card into the PC.

[Cobbydaler]

Good page on Cat5E wiring here (http://www.lanshack.com/make-cat5E.aspx)

[flowrebmit]

You wrote the following in your first post:

<snip>
I took care to cross the wires just at the very end but again that's not something I've ever done before.<snip>

I thought you meant that you had created a cross-over cable - I can't think what else you mean by that sentence.

[alexuk]

You wrote the following in your first post:



I thought you meant that you had created a cross-over cable - I can't think what else you mean by that sentence.

I am so sorry that was not clear at all.

What I meant was that I unrolled the white/coloured pairs and crossed them only at the very end of the connector to avoid and cross interference between them. If you think back at the wiring of a connector you need to separate the green/green-white and "cross" them with the blue/blue-white. I read somewhere that if you unroll them too much in advance there may be cross interference between the channels.

The reason I wrote that is that I was and still am thinking of poor quality signal and thought that I'd unrolled them too much in advance. I did it again making sure only the last bit is unrolled: no difference.

The link posted above states:


Re-use of old cables
We have seen this happen time and time again. Perfectly good patch cables that have been working fine for years, get removed from their installation, and re-installed on the same, or different network. The result can be a nightmare. What happens is that the cable, over time, adapts to the way that it is bent in it's original installation. When these cables are removed and re-installed, they can either completely loose their connection, or develop intermittent problems. This is due to stresses that may be opposite to what they were originally subject to. If the integrity of your network is more valuable than the price of new patch cables, then we strongly suggest that you use brand new cables for all closet cleanups, network moves, etc.


Could it be this is at the root of this problem? I still find it odd the laptop works fine with it.

[Deank]

hi i have a Asus P5N-E SLi nForce 650 mobo