Symptoms

When the first DNS server becomes unavailable for FQDN node resolution, but no ICMP message is received, bigd does not rotate to the next DNS server. In the common case where a DNS server becomes unavailable, an ICMP message will notify bigd of server unavailability, and bigd will rotate to the next available DNS server. However, if network configuration fails to route this ICMP message back to bigd, the DNS server is assumed to remain available (and all subsequent DNS resolve operations will fail, as the DNS server is unavailable).

Impact

bigd continues to send FQDN node resolutions to the (now-unavailable) DNS server, which will fail to resolve (bigd will not rotate to the next configured DNS server). Existing resolved FQDN nodes and all associated monitors will continue to function normally.

Conditions

-- Multiple DNS servers are configured for FQDN resolution for 'bigd' monitors. -- The first DNS server becomes unavailable. -- ICMP messages are not received by 'bigd'. -- BIG-IP software versions earlier than 12.1.3.3 and 13.1.0.

Workaround

Ensure network routes ICMP messages to bigd when the DNS server becomes unavailable.

Fix Information

None

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips