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Checking your ADSL Router operation

Checking your Router

How do I check my Router 'connects' all my PC's OK ?

Most WiFi Routers come with a 'built in' multi-port Switch. In theory, the Switch circuits should be capable of 'learning' the IP addresses of the computers connected to each port, IRRESPECTIVE of the IP addresses those computers are using. Having discovered 'whats where', the Switch will automatically 'link' & pass traffic between any two computers without wasting bandwidth on any of the other ports. This should be supported for both the cabled (wired) and WiFi (wireless) connected computers.

However SOME Routers will only pass traffic between WiFi and wired that is within the Routers own Subnet. In some cases this is due to an over-aggressive Firewall, in others cases (eg BT) it's due to non-standard firmware.

Thus, for example, when a WiFi connected computer uses it's 'Alternate' IP Address to 'connect' to your Server on it's own private IP, the Router's Switch should happily pass traffic between them. Unfortunately, since the Alternate address will be in the Server's subnet (not the Routers), such traffic is often blocked

So, if you want your WiFi computers to access your Server's for backing up (etc.), before configuring your Server in it's own private Subnet you need to check your Router will actually pass traffic to that subnet.

A1. Start by choosing 2 of your computers - one wired, one WiFi and make sure each can 'see' the other at their 'automatic' DHCP (Router issued) subnet addresses.

At each computer, launch a 'command prompt window (Start, Run, cmd) and type 'ipconfig /all'. This will reveal the IP address for that computer (say, for example, they are and On each computer, 'ping' the address of the other (so on, type 'ping' and on type 'ping').

If you have configured your computers using a Firewall (eg CoMoDo or ZoneAlarm etc), you should get 'Request timed out' (as you will have set each computer's Firewall to 'trust' ONLY the single 'Default Gateway' address ( and NOT the entire 192.168.0.x subnet).

In Zone-Alarm, click the 'Your_computer/' pane, click 'View Zones' and (on each computer) ADD the IP Address of the other computer as 'Trusted' (with Setting = Medium).

A2. Once you have confirmed that the DHCP issued subnet addresses are PING'ing OK, add addresses outside the Router subnet range.

On each computer, in the Local Area Connection properties, Internet Protocol (TCP/IP) Properties, Alternate Configuration, User Configured, manually enter an address in the 10.0.0.x range in each (for example and with a Subnet Mask

A3. Make sure the Firewalls on both computers will permit traffic to the other.

In CoMoDo, choose the Firewall tab, select Network Security Policy and adjust the settings as needed (eg add the other computer IP to the Zones, change ICMP Echo Request Policy)

In Zone Alarm, click the 'Your_computer/' pane, click View Zones, click Add, IP Address and add the IP of the other computer. Set this to 'Trusted' (& check that 'Trusted Zone Security' slider is set to 'Medium'). Do this on both computers before proceeding.

A4. If each computer can 'ping' the other, then your Router is passing 'out of subnet' traffic correctly.

At each computer, launch a 'command prompt window (Start, Run, cmd) and type 'ipconfig /all'. This will confirm that the just entered 10.0.0.x IP address has been picked up correctly. Then, on each computer, 'ping' the 10.0.0.x address of the other (so on, type 'ping' and on type 'ping').

If you get 'Request timed out' then your Router is one that refuses to pass traffic outside it's own subnet.

Now go back to each computer and remove both Trusted IP Addresses from CoMoDo / Zone Alarm and remove the Alternate Configuration settings from the computers TCP/IP properties.

What can I do if my Router won't pass traffic outside it's own subnet ?

You will have to configure the Server to use a 'hidden' part of the Router subnet. This is less secure than using a totally different subnet, however careful choice of the DHCP settings (Subnet Mask, DHCP range) can help you 'hide' the Server and confuse any 'intruders'.

Common Router problems ?

Too slow (or too fast) ?

With competition between ISP's all offering 'high speed limitless connection' there is a lot of pressure to squeeze the maximum possible 'bit rate' out of your ancient BT wires. This means that when your Router connects to your ISP it ALWAYS goes through a 'training' phase of checking what speed it can get out of the your noisy BT wires.

If that happens when it's raining and the wires are a bit damp - or the wires are 'blowing in the wind' and the connections are a bit rusty & loose, you may end up with poor SNR & 'loop attenuation' margin and thus very low connection speed .. on the other hand, if the wires are behaving 'perfectly' during 'training' you might get a very high speed that always 'falls over' as soon as you start to use it ...

So resetting (rebooting) your Router at least once a day is a 'good idea' ..

On the other hand, if your Router is actually turned off, the ISP will 'save some bandwidth' by dropping your line .. and when you turn it on again, you may find yourself at the bottom of the bandwidth allocation 'list'

... so, if you must turn off your Router, do so only overnight ..

Noisy line

If your Router keeps dropping it's Internet connection due to 'noise on the line' = low SNR (especially when you pick up the 'land line' phone to answer a call) it may be your 'micro-filters'. These are what separates the high speed Internet frequencies from the low frequency voice (phone) side and these can 'degrade' over time.

One trick I've used is to 'double up' the micro-filters on the voice side (i.e. plug a second filter into the voice line before the actual phone).

You should keep all your internal house wiring as short as possible .. the longer the wires, the more noise they can pick up

Line-line phone gone bad ?

After 2 days of random Internet 'drop outs', Router 'auto-resets', low connection speeds and low SNR margins, I discovered that unplugging my 'land-line' phone cured all the problems, doubled my Router 'SNR margin' and doubled my Internet download speed !

If you can unplug & forget your 'land line' phone so much the better. Most people use mobiles (or Skype) 'all the time' these days and unplugging the land line phone will only mean missing 'marketing' cold-calls and calls from the "I'm from Microsoft and your PC has a virus" 'phishing' fraudsters

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