Last Modified: Aug 19, 2026
Affected Product(s):
BIG-IP LTM
Known Affected Versions:
11.5.1, 11.5.1 hf1, 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, 11.5.1 hf10, 11.5.1 hf11, 11.5.2, 11.5.2 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, 11.6.1, 11.6.1 hf1, 11.6.1 hf2, 11.6.2, 11.6.2 hf1, 11.6.3, 11.6.3.1, 11.6.3.2, 11.6.3.3, 11.6.3.4, 11.6.4, 11.6.5, 11.6.5.1, 11.6.5.2, 11.6.5.3
Fixed In:
12.0.0, 11.5.3
Opened: Jan 30, 2015 Severity: 3-Major
When DNS cache resolver is resolving a DNS query, it might send queries to the backend name server iteratively. If the name server is responding slowly and the cache resolver is sending queries to name servers at a high rate, the CPU usage of the BIG-IP system might be vary high.
The CPU usage might be extremely high. Site might be unstable.
(1) Configure the cache resolver to have a large value (, for example, 40 KB) for both max-concurrent-queries and max-concurrent-udp. (2) The cache resolver sends queries to the name servers at a high rate. (3) The backend name server is responding slowly to the cache resolver.
Configure the cache resolver to have a default value for both max-concurrent-queries and max-concurrent-udp.
The CPU usage does not increase unexpectedly when the cache resolver sends a large number of DNS queries to slow backend name servers.