[Dnsmasq-discuss] dnsmasq DHCP freezing WRAP boards

Simon Kelley simon at thekelleys.org.uk
Mon Nov 28 09:59:11 GMT 2005

Edwin Whitelaw wrote:
> I use the WRAP single board computer running Voyage Linux as wireless 
> routers for my business.  A system that had been running for over a week 
> started locking up approximately once a day after enabling the DHCP 
> functionality of dnsmasq.  When the lockups occurred, I was unable to 
> gain access through either radio (one in managed mode 5GHz, the other a 
> 2.4GHz AP) or the ethernet port.  I did not have access to the console 
> port so can't comment on what might have been displayed there.  DHCP, 
> and everything else would work just fine up until the system froze.  I 
> did not have remote logging enabled at the time but had three customers 
> so needed to get the problem in hand ASAP.  I disabled the DHCP portion 
> of dnsmasq and loaded the ISC DHCP server to replace it.
> The evidence is anecdotal but I have not had any problems so far for 
> over 60 hours, considerably longer than any previous uptime while using 
> dnsmsaq's DHCP.  I am still using the DNS portion of dnsmasq with no 
> problems.
> This post is not really a request for help as I will probably keep the 
> current setup but it might help someone else track down a problem.  On 
> the other hand, it would be nice to have the dnsmasq DHCP functionality 
> as an option going forward.
> I'll provide more detailed system info if needed.
> ---
> riner:~# uname -a
> Linux riner 2.6.14-486-voyage #1 PREEMPT Wed Nov 2 18:14:20 GMT 2005 
> i586 GNU/Linux
> ---

I've not seen any other reports that could shed light on this problem.

How hard is the box locking up? If it's really not responding at all, 
then that must be a hardware problem or kernel bug. (Though it might 
well be triggered by dnsmasq.)

Just a thought: are you relying on this box for the DNS service to the 
machine you are logging in _from_. Maybe the kernel is still up, but 
dnsmasq crashed - hence no DNS. Also is the suspect box relying on its 
own dnsmasq for DNS (ie nameserver in /etc/resolv.conf) 
failure to do reverse lookups can wedge sshd for some time and cause 
strange effects.

On the other hand, if even ping to the dotted-quad IP address fails, 
then the box real has crashed. dnsmasq uses very different syscalls than 
  ISC dhcpd to do low-level network access, so kernel problems with 
those are the obvious first line of attack. One thing you could do is 
re-compile without RTnetlink support: that would eliminate one difference.



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