Bug ID 803233: Pool may temporarily become empty and any virtual server that uses that pool may temporarily become unavailable

Last Modified: Sep 13, 2023

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

Known Affected Versions:
12.1.3,,,,,,,, 12.1.4,, 12.1.5,, 13.0.0, 13.0.0 HF1, 13.0.0 HF2, 13.0.0 HF3, 13.0.1, 13.1.0,,,,,,,,, 13.1.1,,,,, 13.1.3,,,,,, 14.0.0,,,,,, 14.0.1,, 14.1.0,,,,,, 14.1.2,,,,,,,,, 14.1.3, 15.0.0, 15.0.1,,,,, 15.1.0,,,,,, 15.1.1, 16.0.0,

Fixed In:
16.1.0, 16.0.1, 15.1.2,,,

Opened: Jul 08, 2019

Severity: 3-Major


Intermittently (depending the timing of operations that keep MCP busy): 1. Messages similar to the following may be logged in the LTM log, indicating that the virtual server associated with a pool became temporarily unavailable: -- notice mcpd[4815]: 01071682:5: SNMP_TRAP: Virtual /Common/test_vs has become unavailable. -- notice mcpd[4815]: 01071681:5: SNMP_TRAP: Virtual /Common/test_vs has become available. 2. Optionally, if a 'min-up-members' value is configured for the pool, a message similar to the following may be logged in the LTM log, indicating that the number of available pool members became less than the configured value: -- notice mcpd[4815]: 01070282:3: Number of pool members 2 less than min up members 3.


Under these conditions, existing Ephemeral pool members may be removed before new Ephemeral pool members can be created to replace them, causing the pool member to become temporarily empty. This can result in intermittent loss of availability of the virtual server if all records returned by the DNS server for the referenced FQDN change from the previous response.


1. The pool members are all FQDN pool members. 2. The DNS query to resolve pool member FQDNs returns a completely new (non-overlapping) set of IP addresses. (This causes all existing Ephemeral pool members to be removed and replaced with new Ephemeral pool members.) 3. MCP is very busy and slow to process messages.



Fix Information

FQDN ephemeral pool members are created in a more timely manner when FQDN resolution via DNS returns new address records.

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips