Bug ID 427012: dns: fix handling of edns0 queries for TCP and UDP

Last Modified: Jul 12, 2023

Affected Product(s):
BIG-IP GTM, LTM(all modules)

Known Affected Versions:
11.2.0, 11.2.1, 11.3.0, 11.4.0, 11.4.1

Fixed In:
11.5.0, 11.4.1 HF2, 11.4.0 HF4, 11.2.1 HF10

Opened: Aug 02, 2013

Severity: 2-Critical

Related Article: K14851


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.


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


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.


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

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips