The BIG-IP UDP health monitor is designed to work with ICMP Destination Unreachable message responses. When the resource is unavailable and it returns an ICMP unreachable message type in response to the monitor request, the BIG-IP system marks the resource down depending on the ICMP error message returned.
For example, when the UDP health monitor receives an ICMP host unreachable error message in response to the monitor request, it immediately marks the node down.
When the UDP health monitor receives an ICMP port unreachable error message, it notes this as a failure to connect, but will not mark the node down until the health monitor timeout expires.
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