After broadband downtime, Amahi has DNS issues

[dinomic]

Hi all,

This has happened to me at least a couple of times now, and made me look extremely silly to the ISP support people ...

Basically, this is what happens. The cable broadband connection goes down, and then comes back. When this happens, sometimes the ISP's cable modem needs restarting, and sometimes it actually needs both the router AND the cable modem to be switched off for several seconds, the cable modem switched back on, and once all the right connection lights are on the modem switching the router back on. The problem is that, when this seems to happen, the Amahi box then masks a DNS problem. I say that it "masks" the problem because simply restarting DHCP and DNS from the Amahi Web Control panel doesn't seem to solve the issue - the only cure is to completely reboot the Amahi machine (not something I like doing, as it ruins my uptime!! ).

So, what is going no that a simple restart of DNS and DHCP from the web control panel is not fixing? More importantly, are there any debug steps I can take when I have a connectivity problem to check whether the Amahi box is having DNS issues?

[dinomic]

I should also add that, what has convinced me that it's an Amahi DNS issue is that I have machines on the network that are configured for networking as follows:

1) Wireless (with obviously Amahi doing the DHCP and DNS)
2) Wired (with Amahi as the DNS server)
3) Wired (with the ISP's DNS servers set)

When this connectivity issue occurs, only the machines configured as in point 3 above will connect to the internet.

I tried to test this out last night, but stopping DHCP on the Amahi box and temporarily setting the router to control DHCP, but for some reason the Amahi box starts up DHCP again on it's own! Also, on machines that allow for manually "Renewing the Lease" on WiFi connections (e.g. any iOS devices) don't seem to have an effect.

[ciscoh]

II tried to test this out last night, but stopping DHCP on the Amahi box and temporarily setting the router to control DHCP, but for some reason the Amahi box starts up DHCP again on it's own! Also, on machines that allow for manually "Renewing the Lease" on WiFi connections (e.g. any iOS devices) don't seem to have an effect.

Did you disable the watchdog on DHCP?

[dinomic]

Did you disable the watchdog on DHCP?

Good point, ciscoh. I'm relatively sure that I *did* disable the watchdog, but can't be 100% (as by this time, I was a bit flustered with not having fixed the issues). I'll be mindful to check that next time though.

[cpg]

Hi, the description of the actual problem:

the Amahi box then masks a DNS problem

has no details.

what does that mean?

one thing to check is whether the DNS server is running when the problem occurs:

ps guax | grep bind

same for dhcp:

ps guax | grep dhcpd

and that may give some clues.

the next part is to run either dig or nslookup and see if the error is in the DNS server itself or how it looks.

similarly, look a the logs, searching for messages from the DNS server (bind) or the DNS server (dhcpd).