Bug ID 554967: Small Client EDNS0 Limits can Sometimes Truncate DNSSEC or iRule DNS Packets

Last Modified: May 14, 2019

Bug Tracker

Affected Product:  See more info
BIG-IP GTM, LTM(all modules)

Known Affected Versions:
11.4.1, 11.5.1, 11.5.1 HF1, 11.5.1 HF10, 11.5.1 HF11, 11.5.1 HF2, 11.5.1 HF3, 11.5.1 HF4, 11.5.1 HF5, 11.5.1 HF6, 11.5.1 HF7, 11.5.1 HF8, 11.5.1 HF9, 11.5.2, 11.5.2 HF1, 11.5.3, 11.5.3 HF1, 11.5.3 HF2, 11.5.4, 11.5.4 HF1, 11.6.0, 11.6.0 HF1, 11.6.0 HF2, 11.6.0 HF3, 11.6.0 HF4, 11.6.0 HF5, 11.6.0 HF6, 11.6.0 HF7, 11.6.0 HF8, 12.0.0, 12.0.0 HF1, 12.0.0 HF2

Fixed In:
12.1.0, 12.0.0 HF3, 11.6.1, 11.5.4 HF2, 11.4.1 HF10

Opened: Oct 29, 2015
Severity: 2-Critical

Symptoms

A resolver sending a query with a small EDNS0 UDP buffer limit can lead to packet truncation. These response packets are flagged as truncated in the header, but the OPT record might be cut/missing leading some resolvers to consider the packet malformed.

Impact

Some resolvers regard OPT-less truncated packets as malformed and cease follow-up requests via TCP or a larger EDNS0 UDP limit.

Conditions

Primarily via dynamic settings such as iRules on DNS_RESPONSE events adding new records, or DNSSEC record signing with responses over UDP.

Workaround

none

Fix Information

Truncated DNSSEC or iRule DNS packets are RFC-compliant.

Behavior Change