Network Issue MBP can connect, TV can't (via ethernet)

jaybeeveedub

Hi All,

My limited networking knowledge has been overwhelmed by a peculiar issue I have encountered.

When our house was being rewired we had Ethernet points put in in various locations throughout the house. We just bought a new TV and when I tried to connect it up I immediately came across issues.

For background here's my system, which worked perfectly...

Provider
0. UPC - Thomson Router - Managing Addresses - Wireless Off
This then distributes via Ethernet to:

1. an Apple Airport Extreme which generates a WiFi network via bridge mode
2. two further Airport Express devices which extend the network due to thick walls
3. SKY+ Box
4. NAIM UnitiQute

When we got the second TV I connected it via Ethernet to the point put in precisely for this purpose, but which hadn't been used up till this point.
I had no success in connecting using DHCP (it self-assigned an IP address in the 192.168.254.XXX range rather than the UPC range of 192.168.0.XXX)
I tried using a static IP address and at first I thought this had worked as the MAC address of the TV popped up in the UPC router's admin panel.
However the TV couldn't connect to the internet (using google DNS).

Next I tried doing the same thing at the same location using the newly arrived SKY box... same issue.... (both devices were able to connect via WiFi no problem, but our walls are very thick and Netflix over wifi rarely manages HD for us)

So far so negative, Samsung had no answer beyond making sure to use Google DNS...

My next step however is where the peculiarity arises;

I plugged my MacBook into exactly the same Ethernet port, with WiFi switched off and I instantly connect to the net, speedof.me showing 60Mbps Down and 12 up...

This tests the limits of my understanding of networking....

However it gets weirder again, I decide as a stop gap measure to bring the Airport Extreme into the same room as the new TV, connect it to the Ethernet port and at least have super strong wifi right beside the TV....

no joy, Airport Express can't connect to the internet....

instinct tells me that my (sh1t3hawk of an....) electrician has damaged the Ethernet cable somehow, but if that were the case, how can my MacBook connect perfectly, and using static IP how can I connect to the router but not to the internet!!

The Airport Express setting did not change in any way, all that happened was the 20cm Ethernet cable used to connect to the UPC router was replaced with the 30ft cable connecting the Ethernet point to the UPC router, I have no issue doing the same thing with a 60ft Ethernet cable which is connecting to the original sky box and airport express

Any and all help would be much appreciated!

Cheers

JB

ED E

Sounds like a crappy cable. TV is able to ARP bcast (layer 2) so its MAC will appear but then L3 communication fails. MBP has a better NIC and manages a connection.

I've a dodgy run at home that I'm yet to replace to a samsung TV, it really struggles while any laptops connected are stable for hours. Crappy NICs embedded in their TVs I suspect.

Is your UPC 120/12 or 240/24? If either you should expect 85-95Mb on 10/100 ethernet, not 60, so another sign its not great.

A cheap cable tester will let you know at least if all 8 pins are operational, a good tester won't be economical.

jaybeeveedub

ED E wrote: »

Sounds like a crappy cable. TV is able to ARP bcast (layer 2) so its MAC will appear but then L3 communication fails. MBP has a better NIC and manages a connection.

I've a dodgy run at home that I'm yet to replace to a samsung TV, it really struggles while any laptops connected are stable for hours. Crappy NICs embedded in their TVs I suspect.

Is your UPC 120/12 or 240/24? If either you should expect 85-95Mb on 10/100 ethernet, not 60, so another sign its not great.

A cheap cable tester will let you know at least if all 8 pins are operational, a good tester won't be economical.

Cheers ED E....

in terms of a tester, would somewhere like eurosales stock a cheap one?

Or am I better to get a spark to call over ( I could get him to replace the random 3 rj11 sockets installed by my guy)

in fact, thinking on that, would a poor connection cable to socket cause the same issue?

JB

Cuddlesworth

jaybeeveedub wrote: »

Cheers ED E....

in terms of a tester, would somewhere like eurosales stock a cheap one?

Or am I better to get a spark to call over ( I could get him to replace the random 3 rj11 sockets installed by my guy)

in fact, thinking on that, would a poor connection cable to socket cause the same issue?

JB

It would be worth taking out the RJJ45 sockets and making sure the 8 cables are pinned correctly and that they are making full contact.

On the off chance, what would be the distance between the start and end of this cable?

ED E

Eurosales might do them, never shopped there.

I've used one of these before:
http://www.amazon.co.uk/Komodo%C2%AE-Ethernet-Network-Cat5e-Tester/dp/B00DN197DE/ref=sr_1_3?ie=UTF8&qid=1450276826&sr=8-3&keywords=cable+tester

Cheap as chips but does the basic function of ensuring a connection on each pin. The next step up is a real tester.

jaybeeveedub

Cuddlesworth wrote: »

It would be worth taking out the RJJ45 sockets and making sure the 8 cables are pinned correctly and that they are making full contact.

On the off chance, what would be the distance between the start and end of this cable?

I'd say roughly 30 feet?

I had thought about signal degradation over a a very long run, but the working run to the sky box elsewhere is a good deal longer.

Alun

It's worth pointing out also that it matters exactly how the 4 pairs in the cable are connected to the pins in the connectors. I've seen too many network cables terminated by electricians where each pair is sent over adjacent pins rather than wired correctly according to T-586B. An el-cheapo "cable tester" that just detects continuity won't check for such mistakes.

ED E

Alun wrote: »

It's worth pointing out also that it matters exactly how the 4 pairs in the cable are connected to the pins in the connectors. I've seen too many network cables terminated by electricians where each pair is sent over adjacent pins rather than wired correctly according to T-586B. An el-cheapo "cable tester" that just detects continuity won't check for such mistakes.

The lights actually do tell you which pin the return comes on, so if you cross/miss cross you'll see it, or a ground.

Its also not uncommon for sparks to share one cable for two runs, which you can do but it limits you to 10/100 and isnt great for performance.

Alun

ED E wrote: »

The lights actually do tell you which pin the return comes on, so if you cross/miss cross you'll see it, or a ground.

That's not what I meant.

It's possible, for example, to (incorrectly) wire patch lead in such a way that each pair is wired to adjacent pins, i.e. 1&2, 3&4, 5&6 and 7&8. This will pass a simple DC continuity test with flying colours but will fail miserably as a network cable that has to carry high frequency signals.

This is because the pairs on a correctly terminated plug should be wired to 1&2, 3&6, 4&5 and 7&8 as per T-586B. It might seem odd, but that's the way the pins are wired on the sockets on Ethernet cards and on switches etc.

If you connect such a "straight through" cable between an Ethernet card and a switch, you get what is known as "split pairs", i.e. the +ve and -ve Tx and Rx signals on pins 4&5 and 3&6 will actually travel over one half of two separate pairs which causes all kinds of nasty crosstalk problems.

There are testers that can test for this but they're quite a bit more sophisticated and therefore expensive than the "battery and 8 LED" type you'll find on fleabay and the like.

Believe me, I've been there and done that ... I did a job a while back where some well meaning contractor had wired an entire building with several hundred connections like that and had to be called back to redo the lot.