Random lockups — the DNS relay issue

The problem

You are experiencing apparently random router lockups (ie the green status LED is either solid green or not lit at all) and you are running P2P software or other software which performs lots of DNS lookups (ie resolving host and domain names to IP addresses), then the most likely cause is that the large number of DNS lookups is filling all available memory.

In fact the router has not actually "locked up". If you connect to the router's serial console port (see instructions for doing this), and wait for it to lockup again, you will notice that it has dropped to the DEBUG prompt and provides an error message telling you which module caused it to do so. If this error message mentions the DNS relay module, then this is indeed your problem.

The solution

Log on to your router with your web browser using its web interface and:

1. Select the Proxy DNS option from the Configuration menu on the lefthand side;

   • change the Proxy DNS option in the drop down menu on the righthand side from enabled to disabled;

   • write down the DNS server IP which is currently shown (you need this later);

   • click the OK button and select Continue and Save Changes Later;

2. Select the DHCP Configuration on LAN option from the Configuration menu on the lefthand side;

   • if the State option on the righthand side is enabled, proceed with this step. Otherwise, skip to Step 3 below.

   • change the Primary DNS option by entering the IP address which you wrote down earlier into this field;

   • click the OK button and select Save changes and reboot the system now.

   • You have finished!

3. You have reached this step because the computers connected to the router do not obtain their IP addresses from the router's DHCP server. This will normally be the case because you have assigned static IP addresses to these computers and have also assigned the router's IP address as the IP address of the primary DNS server.

   You will need to change the IP address of the primary DNS server from the IP address of your router, to the IP address which you wrote down earlier. Excatly how you do this depends on what operating system (eg Windows 95, 98, ME, NT, Win2K, XP, Win2003, Linux, FreeBSD, OS/2, Solaris, OS X, etc) you are using.

Additional notes for those running P2P software

If you are running P2P/file sharing software, then you should also consult the Definitive Guide to Frequent Disconnections for details on tuning the router to work reliably with your applications.

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