In what circumstances would a DNS server request timeout when the forwarders already have the answer? For example, there appears to be a domain that I assume is having DNS issues at the moment us.army.mil. If I hit the forwarders directly with nslookup for type=mx then I get a response right away. If I hit our DNS server though with the same request it takes more than 2 seconds and times out or when I extend timeout to 10 seconds it fails. If I try multiple times it eventually returns a response.
It is my understanding that our DNS server should be sending requests for external domains to the forwarders and getting response if available. The log shows the first forwarder being hit and then after 3 seconds the second forwarder is attempted. How does my direct request to the forwarder not have problems while our server's does?