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DNS server timeout

We have a problem with dns resolution of a mx record that causes mail to backup and eventually lead to a NDR.

From my investigation it is a result of our DNS server not responding with the requested information for a mx query.

today:  from mail server to DNS1 server

set type=mx

request timed out.

A DNS request to our secondary dns server (DNS2) give us the requested information.

When i restart DNS on DNS1, the query gives us the same  correct information and mail starts to flow.   I am not sure what is causing this.   Any thoughts?

We do not use forwarders, just root hints.  Both DNS1 and DNS2 servers are configured identically as far as i can tell.

DNS1 is the primary server for all DNS for our environment.
2 Solutions
Ian MeredithCommented:
Do you have MX entries in your DNS?
Andrej PirmanCommented:
It might also be an issue with your router/firewall. If you have Cisco check the rules, it might in some cases block incoming queries considering they are an attack.

Also, check BINDING of your DNS1 - it should be binded to single NIC adapter, the one, which is resolved in outside world directly or via NAT.

Another thing - you say you use root hints only.
I would recommend your server's NIC adapters to use local DNS on server (itself), and local DNS (on server) to have forwarders configured.

It might be your router/firewall which messes with DNS queries.
For example, outside query for a zone on your server comes in, your server's DNS is bind to internal adapter, so query gets resolved by using DNS from server's NIC adapter, which is your router. Your router forward query to your server's DNS via LAN adapter, and tries to report it back to querier, but ARP table is messed up with same queries coming from inside and outside side.

Disable IPv6 on DNS.
"When i restart DNS on DNS1, the query gives us the same  correct information and mail starts to flow."
If the DNS service is stopping for some reason, there must be a related entry in the system event log.  Probably under DNS or System.  That's where you should start the search for the cause of the service stopping, esp. if it runs fine for a while and then just suddenly stops.
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egrotjahnAuthor Commented:
the DNS service was not stopping, just forwarding requests wasnt working.   I installed updates to the Server and rebooted it.  DNS has had no issues today.   I searched the event logs and found no error
Andrej PirmanCommented:
Do you have any VPN connection active to maybe some other site, which has it's own DNS? In this case DNS queries might be forwarded to the other side of VPN for the other DNS to answer. Check it out with by typing:
and see, which server is returned by default.
egrotjahnAuthor Commented:
the server was out of date with respect to updates.   I applied them and rebooted the server and all services have been responding as they should.   thanks for the help.

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