Not all devices on wired Network working.

[netdummy]

Hi,

I ran 3 x 10m network cables under the floorboards of my house to various rooms and cut off the ends and terminated them to RJ45 keystone jacks and wallplates.

I then connected the 3 'router ends' from wallplate to router and tested all the other end connections by plugging in an old xp laptop.

The laptop picked up an IP from the router and had internet access so I assumed all was well.

I'm now finding that some networked devices will pick up an IP and work and some wont.

Devices that will work are:
The aforementioned XP laptop
& a WD Live

Devices that wont work are:
AV Receiver.
Raspberry Pi.

The devices that don't work on my DIY cabling are verified as working when I plug straight into the router.

I assumed either everything would work or not work.
How can this happen?

thanks in advance for any help.

[TonyH]

Hi,
I'd double check the cables you made.
Good luck.

[netdummy]

Yeah, I know the cables must be dodgy.

My question is why would some devices work and not all?

If the cables are no good I would have expected nothing to work.

[Nerre]

This is a wild theory, but I think it could be a matter of whether the devices can handle crossover cables or not.

In the good old days normal cables were straight, in a network switch or hub the pins corresponding to the devices TX were RX and vice versa. This meant a straight cable could be used to connect a computer to a network switch or hub.

For uplink between two network switches you needed a crossover cable (cross-connecting TX to RX) because otherwise you would connect TX to TX and RX to RX.

Later on network switches were designed with a dedicated uplink port, which could be switched over between "straight" and "crossed" (manually or automatically). This meant you could always use straight cables (but crossover could still be used between network switches).

Modern network switches have autodetect for uplink on ALL ports (meaning any port can be used as uplink). This means they can handle both straight and crossover cables.

I think maybe also modern NICs for computers can have autodetect. If both ends support autodetect they might be able to negotiate a connection on "the wrong pairs" in the cable if "the right pairs" are not working. But if only one end supports autodetect this will fail.


I bought a cheap cable tester a week ago because I have always hated not knowing if the cable is working or not... And it's a pain to test using a multimeter or a buzzer of the ends of the cable are far apart. Now I just plug in the two parts of the tester in each end and watch the LEDs and see if there is open circuit or if some leads are crossed.

[netdummy]

Thanks for the reply Nerre.

That sounds plausible. I IDC'ed the cables pin to pin myself.

I think I'll invest in a cheap cable tester as it's annoying me not knowing what the problem is.

[netdummy]

I bought a cheap cable tester and it appears I have an open on pin 3 on both cables.

Very odd that it would be the same 1 on 2 cables. Need to check if the keystone jacks I bought are dodgy.