DNS Resolution Problem

[wrj0]

Recently my ISY began experiencing DNS resolution problems. DNS resolves properly for four hours after a system reset during which time NTP Time sync, Climate Module data, and ISY outbound email all function properly. However, after four hours of proper operation, the ISY starts reporting DNS Errors for both NTP Time and the climate module, and outbound ISY email ceases. Once the DNS errors start, I can replace the ISY's NTP time server URL with the time server’s ip address and can force the ISY to perform a time sync just fine, so Internet connectivity seems OK. Two other devices on the local network, an ELK and a Wi-Fi router are configured with the same DNS server ip (from the local ISP) that is set in the ISY, and both the ELK and Wi-Fi router resolve DNS properly; just the ISY experiences the DNS resolution error.

 

The problem started after upgrading the ISY from 2.8.7 to 2.8.16 and after enabling ISY-ELK communication (both changes made about the same time - OK, bad move on my part!). So, I removed the ELK parameters from the ISY, and disconnected both the ELK and the Wi-Fi router from the local network to try to isolate the problem, but the ISY continues to show DSN errors around 4 hours after a system restart. I’ve also tried setting CWT=30,000, but that didn’t help.

 

The ISY is connected to a PIX501 that when restarted allows the ISY to properly resolve DNS for 4 hours, then the ISY DNS resolution errors start again until the PIX is once again restarted or reloaded. The ISY is assigned a static ip on the local network and worked fine for a couple of years in this configuration (with the PIX) until I upgraded the ISY and established the ISY-ELK link. Now with only the ISY connected to the PIX, the DNS resolution errors start appearing four hours after restarting the PIX. The ISY Error log shows “System -100 [Network] DNS Server N/A,†but the other devices, if connected, resolve DNS properly.

 

Since I've not changed the PIX configuration, I'm curious if anything may have changed in ISY since 2.8.7 that I need to accommodate in the PIX to eliminate these DNS errors. Suggestions, please?

Thanks.

[Michel Kohanim]

Hello wrj0,

 

One of the problems is that in 2.7.15 ISY didn't report on DNS/network errors as extensively as it does now. So, that might be one of the reasons you see so many of them in 2.8.16.

 

The first thing I would check is the interval between DNS errors for the WB module. If it's NOT equal to your polling interval, then it seems that the problem is that there are some DNS errors and they correct themselves.

 

The other thing that might help is to change your ISY's IP configuration to DHCP (with a reserved IP address) and see if that improves the situation.

 

With kind regards,

Michel

[wrj0]

Thank you for your response and suggestions, Michel. I’ve tried both DHCP and static addresses in the ISY, but the DNS problem remains.

 

The Climate module is set to poll for data every 120 seconds, but the DNS failure only occurs 4 hours after resetting the PIX501. I've tried to capture the cause of the failure in the PIX501, but the 4 hour delay before the error occurs is maddening. Taking the PIX out of the network allows the ISY to resolve DNS just fine, so the problem is with the PIX. Curiously though, other local network devices connected to the PIX don't have any DNS resolution problems and it worked fine with the ISY for a couple of years prior to upgrading to 2.8.16.

 

Frustration got the better of me, so I’ve replaced the PIX with another firewall device that does not experience the DNS problem.

Thanks again.

[Michel Kohanim]

Hello wrj0,

 

I would probably be more frustrated. I cannot stand unexplainable behavior.

 

Please do keep us posted with any other anomaly.

 

With kind regards,

Michel