DNS problem?

[Alan Curtis]

On 6/8/05, John Brooks <john at day-light.com> wrote:
> > I am running a FreeBSD server behind a Linksys Wireless Access
> > Point / Router (BEFW11S4). Its local address is 192.168.1.1. The
> > Linksys is attached to a DSL modem.  In my /etc/rc.conf file I have
> > defaultrouter=192.168.1.1
> > which works most of the time. However occasionally, all network
> > traffic freezes, I cannot login to the server using ssh and my
> > mailing lists and websites do not function. If, at my server, I type
> > "host someip.com" it reports 'no server can be found' or some similar
> > message (I sorry, I didn't note down the exact message) - a reboot
> > has fixed the problem.
> >
> > I assume that the problem is that the server is unable to find a DNS
> > server. Is that right?
> 
> Probably...
> 
> > Do I have it right that I should point defaultrouter at the firewall?
> 
> Assuming that the firewall is your gateway to the outside world, then
> yes.
> 
> > How do I tell FreeBSD about other DNS servers to use if the firewall
> > route fails?
> 
> If your resolving dns servers as listed in /etc/resolv.conf are outside
> the firewall, then they cannot be reached if the default route is down.
> Likewise if your resolving dns servers are inside or on the firewall, then
> their queries will never be answered. The effect is the same, you don't get
> an answer. Unless they have some cached results that have not yet timed out,
> but even with the cached answer you still cannot reach the destination,
> so the end effect is the same - you know where to go but cannot get there.
> 
> > Why does pointing defaultrouter at the filewall fail?
> 
> Cable unplugged, switch down, nic dead, firewall down, upstream isp out,
> isp router down, electricity out, hard drive on firewall crashed, dsl/cable
> modem out, telco burped, and so forth for another hundred possible
> reasons...
> 
> You could start troubleshooting by these steps:
> 
> 1) ping 127.0.0.1
> 2) ping ip of local machine
> 3) ping localhost
> 4) ping hostname of local machine
> 5) ping another host on same lan by ip address
> 6) ping another host on same lan by hostname (if any exist in /etc/hosts)
> 7) ping interior ip of firewall (192.168.1.1)
> 8) ping exterior ip of firewall
> 9) ping default gateway of firewall
> 10) ping ip address of some internet host (yahoo.com = 66.94.234.13)
> 
> As you proceed down this list it will give you clues as to what is wrong,
> and tell you where to look. Good luck...
> 
> >


Thank you John.

I will try this series of pings the next time my server freezes. I did
try something similiar, if not so methodical last time it froze and
could ping most things on the interior. The firewall was still working
as I could still access the outside using other computers on the
network, so I think the problem was with the server somehow.

Alan