Symptoms

There is no option to change the DNS UDP truncation value to something other than 512 bytes.

Impact

Certain network topologies that might require the UDP DNS to be passed through or have a higher limit cannot configure for it.

Conditions

Using DNS UDP truncation.

Workaround

None.

Fix Information

There is now a DB variable to control DNS UDP truncation behavior: dns.udptruncate. When dns.udptruncate is enabled, UDP DNS responses are truncated if the response is larger than 512 bytes. When dns.udptruncate is disabled, the message is not truncated, and the full message is received. If the client specifies a non-default size via EDNS, the message is truncated if the response is larger than the specified size regardless of the value of dns.udptruncate.

Behavior Change

There is now a DB variable to control DNS UDP truncation behavior: dns.udptruncate. When dns.udptruncate is enabled, UDP DNS responses are truncated if the response is larger than 512 bytes. When dns.udptruncate is disabled, the message is not truncated, and the full message is received. If the client specifies a non-default size via EDNS, the message is truncated if the response is larger than the specified size regardless of the value of dns.udptruncate.