VRRP Command Reference
248 7705 SAR OS Router Configuration Guide
Unlike other priority event types, the host unreachable priority event monitors a repetitive task. A
historical evaluation is performed on the success rate of receiving ICMP echo reply messages. The
operational state takes the cleared and set orientation from the historical success rate. The
informational portion of the operational state is derived from the result of the last attempt. It is possible
for the previous attempt to fail while the operational state is still cleared due to an insufficient number
of failures to cause it to become set. It is also possible for the state to be set while the previous attempt
was successful.
When an event transitions from clear to set, the set is processed immediately and must be reflected in
the associated virtual router instance in-use priority value. As the event transitions from clear to set, a
hold-set timer is started with the value configured by the event’s hold-set command. This timer
prevents the event from clearing until it expires, damping the effect of event flapping. If the event
clears and becomes set again before the hold-set timer expires, the timer is reset to the hold-set value,
extending the time before another clear can take effect.
The hold-set timer must expire and the historical success rate must be met prior to the event operational
state becoming cleared.
The no form of the command deletes the specific IP host monitoring event. The event can be deleted
at any time. When the event is deleted, the in-use priority of all associated virtual router instances must
be re-evaluated. The event hold-set timer has no effect on the removal procedure.
Default no host-unreachable
Set – host unreachable ICMP host unreachable message received for drop-count consecutive
attempts
Set – no reply ICMP echo request timed out for drop-count consecutive attempts
Set – reply received Last ICMP echo request attempt received an echo reply but
historically not able to clear the event
Cleared – no ARP No ARP address found for IP address – not enough failed attempts to
set the event
Cleared – no route No route exists for IP address – not enough failed attempts to set the
event
Cleared – host unreachable ICMP host unreachable message received – not enough failed attempts
to set the event
Cleared – no reply ICMP echo request timed out – not enough failed attempts to set the
event
Cleared – reply received Event is cleared – last ICMP echo request received an echo reply
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