Symptoms

BIG-IP did not truncate DNS responses (for non-EDNS0 queries) to 512 bytes. On TCP a query w/ or w/o EDNS0 may also be truncated.

Impact

The message may be too large over UDP; or it may be truncated over TCP.

Conditions

A query with or without EDNS0 against DNS-Express or DNS Cache. On UDP, the query should be truncated to 512b if no EDNS0 is sent; of course if an EDNS0 max udp size is set, then truncate to that value. On TCP a response should never be truncated.

Workaround

An iRule may be written to keep track of query ID and conditionally truncate the response.

Fix Information

BIGIP no longer truncates DNS over TCP; nor does it send more than 512 bytes over UDP when edns0 is not present.

Behavior Change