Last Modified: Sep 01, 2026
Affected Product(s):
BIG-IP TMOS
Known Affected Versions:
17.5.1.8
Opened: Aug 05, 2026 Severity: 3-Major
On affected versions, BIG-IP may not properly refresh the runtime ICMP Echo response state when the availability of an associated virtual server changes. When all pool members become unavailable, the virtual server transitions to an unavailable state; however, the virtual address may continue responding to ICMP Echo requests. Conversely, after the virtual server returns to an available state, the virtual address may remain unresponsive This behavior has been observed with more than one ICMP Echo mode, including Selective and All, and is not limited to Selective mode.
The virtual address may retain a stale ICMP Echo response state after the associated virtual server changes availability: - It may continue responding to ICMP Echo requests after the virtual server becomes unavailable. - It may remain unresponsive after the virtual server returns to an available state. - ICMP-based monitoring may therefore report a virtual address state that does not reflect the current status of the virtual server. - Reapplying the ICMP Echo configuration may be required to restore the expected behavior.
- A virtual address is configured with an ICMP Echo mode that permits responses, such as Selective or All - All members of the pool associated with the virtual server become unavailable, either because they are marked down by a monitor or forced offline - The virtual server subsequently transitions from available to unavailable, or later returns to an available state
Toggle and reapply the virtual address’s ICMP Echo configuration with the following two-step process: - Change the ICMP Echo setting to Disabled - Change it back to its original mode, such as Selective or All This rebuilds the ICMP response state and restores behavior consistent with the current virtual server status
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