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Aim

I have an existing WiFi router and network, with both wireless and wired devices. However, I need to expand the size of my WiFi network. I have an Ethernet connection between two parts of my house, and I want to create a second WiFi access point at the other end of that connection.

Problem Description

I'm attempting to expand my home network using WAN Bypass (using two routers, with only one serving as the DCHP server, and the other as a WiFi access point only - details on Whirlpool). During testing, I connected both routers with a short Ethernet cable while they were sitting next to each other.

[Internet]--[Router A] ==== [Router B]

This works perfectly, as proven by being able to access all IP addresses and internet access from either access point, both WiFi and wired.

I have wired in the walls of my house an Ethernet cable from upstairs to downstairs. It is not a crossover cable.

When I connect the same WAN Bypass, but using the wall cable, it fails.

[Internet]--[Router A] ====|==== [Router B]

Router A and Router B are unable to see each other over the network. Sending a ping results in 100% lost packets. Devices connected to Router A are still able to connect to the internet, as usual.

I have also tested the cable in the wall.

[Internet]--[Router A] ====|==== [Computer]

This works perfectly, and the computer is able to connect to the network, access all IP addresses and the internet.

I have, of course, swapped out all the intermediate Ethernet cables.


Additional Information

Please ask if you need any more information!

  • I reside in Australia, and am connected to the internet using an ADSL 2+ connection. I live less than 2km as the bird flies from the local exchange, which has plenty of space
  • Router A is a D-Link DSL-2740B-F1
  • Router B is a NetComm NB504
  • The wall cable is approx. 20m long

2 Answers 2

1

This is indeed a strange one.

Officially, if you connect two devices of the same layer you must use a crossover cable. Most devices will auto-detect this and it will work anyway, but in some rare cases they won't. Note that the WAN part of the router is considered L3 while the LAN part is usually considered L2 in home routers. So if you connect Router-2-Wan with Router-1-LAN, normal cable is ok, but if you connect Router-2-LAN and Router-1-LAN, it should be a crossover.

So, if the short cable is crossover, make the long one the same. If that is not the case, check the long cable connectivity wire by wire. Although there is not gigabit connection forming, there may be an improper contact problem.

2
  • With Router B being an older Router, it's possible it doesn't have support for auto-detecting crossover or not. The only other thing I haven't done, is check the long cable with a proper Ethernet tester thingo (you know, where it sends an electrical pulse down each wire in sequence, and there's LEDs at the other end). I'll see if I can scavenge one from somewhere... I don't particularly fancy buying it.
    – nchpmn
    Mar 23, 2015 at 6:58
  • You can check with a multi-meter if you have one available. Short out all pins on one side and measure resistance on 100 or 1kohm scale between the pins at the other end. It should be a very low value.
    – Overmind
    Mar 23, 2015 at 7:03
1

I would look at the copper grade, pinout, and twisted-pair pairings of the in-wall wiring. It could be that you have a defect in your wiring that your computer's NIC is able to deal with, but your router B isn't able to. I'd also look at which port you're using on Router B.

The computer's NIC may do auto-crossover (auto MDI-X), but maybe your router doesn't.

Or maybe the first and second pairs (pins 1&2, 3&6), which are used by 100BASE-TX, are wired correctly, but there's something wrong in the third or fourth pairs (4&5, 7&8), which are required for GigE. Maybe your computer's NIC is autonegotiating down to 100BASE-TX, but your router is still trying to do GigE and failing.

Note the pairings I highlighted in the paragraph above. Those pin pairs need to to be twisted together in the cable. This isn't something a typical dumb pinout tester (or multimeter/continuity tester) will be able to tell you. You can have the right pinout but still have the wrong conductors twisted together, which breaks the magic of UTP and differential signaling that 10/100/1000BASE-T relies on.

Maybe someone tried to re-use voice grade telephone wiring (Cat3 or less), whereas both 100BASE-TX and 1000BASE-T require at least Cat5. Maybe your computer's NIC is high enough quality to still manage to make a link, but your router isn't as good.

Check what ports you're using as well. Maybe when you moved Router B to the other location, you changed which port on Router B it was plugged into. Some routers allow their WAN port to act as a LAN port when they're in bridge mode (i.e. not doing NAT and DHCP server), but others don't. If you have one where the WAN port does NOT act as a LAN port, and you accidentally connected to that one, you'd have a problem.

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