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Troubleshooting steps

Common Troubleshooting Steps:

Green text applies to CLASS I routers only




Diagnostic testhttp://

When posting, please include as much information as possible.

Please include the system log if you are having problems getting online etc:

Preview your post, in case the formatting is all wrong (tables etc from the router do not copy well). Paste into something like Notepad, to remove all the formatting first.

Include model number, what type of cable you are using (USB or Ethernet), the firmware you have (including version etc).

The steps above are very common on the forum and are a way of finding out what is wrong with your router. Please go through them and include the results in your post, to save time later on.

ASR8400 LEDs/Lights

Normal Behaviour
PWR – Power ON, Not Flashing
LINK Flashes when router is switched on, stays ON when router is connected to the Internet
LAN 1 to 4 Flash when connected to a device (only when there is some activity)

ASR8100 LEDs/Lights

Normal Behaviour
PWR – Power ON, Not Flashing
RDY Flashes when there is some ‘system activity’
WAN + LAN Flash when connected to a device (when there is some activity)

ASR8000 LEDs/Lights

Normal Behaviour
PWR – Power ON, Not Flashing
RDY Flashes when there is some ‘system activit


Synching problems? Can’t connect to the Internet or ISP?

Check the following:

On the router

  • Check the diagnostics test and system log (these should help in seeing where the problem is appearing) – see
    previous post above.
  • Obviously the ISP login details (username and password) need to be correct. Make sure there are no
    typos, these must be exactly as given by the ISP and are case sensitive. Also make sure they are entered in full, including any “@” or “.com” etc.
    Some ISPs don’t provide a password, just a special username.
    Even without these details, a router can normally synch with the exchange (the ADSL LED light will stay on when this happens).
  • The main settings for establishing a connection are correct.
    For a normal BT based ISP – Encapsulation=PPPoA VC-Mux, VPI=0 and VCI=38.
    Also typically MTU=1492, MRU=1492 and MSS = 1452 (1432 is the default which is OK too).
    These may be different depending on your ISP so please check with them for the correct values.
  • The SNR margin and Attenuation values are reasonable – for example:
    SNR margin (higher the better) : 25-30dB is normal, below 6dB is a real problem
    Line Attenuation (lower the better) : 10-20 is normal, above 40 is a real problem
  • Make sure your router isn’t getting too warm/hot – ensure it has adequate ventilation and that it is not
    crammed in a small space.

In the house (or wherever you happen to live)

  • All the cables are in good shape and plugged in fully.
  • The microfilters are good quality and fitted to any phone equipment.
  • The router/modem is either on a good phone extension or better still, connected to the Master BT socket.
  • The distance from the exchange is not too great (if you are too far away then the signal may be too weak).
  • Check the wiring on your sockets (especially extensions) is correct. Unfortunately telephone wiring (in
    the UK) is not as standardised as it should be so you may find wires (or pairs of wires) missing or swapped round. You may find the signal quality improves dramatically when the wiring is corrected. See THIS post from NickS and for help on the subject.


  • It’s possible the fault lies with BT or the ISP – if this is the case they may take some persuading to investigate or to admit to a fault. If you’re unlucky, the fault may be intermittent and only appear at odd times. This kind of problem is very difficult to track down and solve so you will need to persevere and have plenty of patience.
  • If the signal is very weak you may find that the router simply won’t synch – if the ISP says that’s tough then
    you may need to experiment with different routers/modems are some are better for weak signals than others (e.g. Alcatel based modems seem to be better than others).

Generally, as the connection speed increases the SNR will decrease (that’s physics for you!). That means if your SNR is 24dB at 1Mbps it might be around the 6dB mark at 8Mbps. The graph below shows these trends for different examples. In reality the SNR cannot go below zero, so if your SNR is 20dB at 1Mps it would be around zero at 8Mbps (which would not be usable, of course):


This post is basically a combination of various bits of information already in the forum, all put into one. Any links with in them may be different for your router if the IP or firmware is different.

Further suggestions:

Trying the ‘hidden’ socket –

Microfilters –

Last updated by Neo on Saturday, August 29th, 2009
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