Amer Networks E5Web GUI - Manual (Page 95)

The Link Monitor is a cOS Core feature that allows monitoring of the connectivity to one or more
IP addresses external to the Clavister Security Gateway. This monitoring is done using standard
ICMP "Ping" requests and allows cOS Core to assess the availability of the network pathways to
these IP addresses. The administrator can select one of a number of actions to occur should a
pathway appear to be broken for some reason.
Link Monitor Actions
If sufficient replies are not received to link monitor polling, cOS Core makes the assumption that
the common link to those IP address is down and can then initiate one of 3 configurable actions:
• A cOS Core reconfigure.
• A High Availability (HA) cluster failover.
• An HA cluster failover followed by a cOS Core reconfigure.
Monitoring Multiple Hosts
A single Link Monitor object can monitor a single host or it can monitor multiple hosts. When
monitoring a single host, either a failure of the host or the connection to the host can cause the
monitor's action to be trigger.
When multiple hosts are specified for a single Link Monitor object, more than 50% of the hosts
have to be unreachable for the object's action to trigger. This is useful when it is the availability
of the connection to the hosts that is important and not the hosts themselves. If it is the
availability of a single host that is important then a Link Monitor object should be created that
monitors only that host.
The Link Monitor Reconfigure is Different
The reconfigure that can be triggered by the link monitor has one special aspect to it. The link
monitor reconfigure has the additional action of restarting all interfaces. This means that if there
is a problem related to a particular Ethernet NIC, perhaps due to overload, then this can be
cleared by interface initialization. This results in only a momentary delay in throughput while the
reconfigure takes place.
Link Monitor Uses
The Link Monitor is useful in two distinct scenarios:
• An external device develops an occasional problem with its link to the Clavister Security
Gateway and the physical link needs to be renegotiated. Such problems can occur sometimes
with some older equipment such as ADSL Modems. For this scenario action 1. Reconfigure
should be selected.
A reconfigure means that the cOS Core configuration will be reloaded. All connections and
states are saved but reloading means all traffic is suspended for a short period and all
interface links to external devices are renegotiated.
• In an HA cluster setup, the link from the master to the external Internet (or other part of a
network) can be continually monitored so that should the link fail, the slave will take over
(assuming that the slave has a different physical connection to the monitored address). The
action chosen for HA should be either 2. Failover or 3. Failover and reconfigure.
If the first action option 1. Reconfigure is chosen in an HA cluster, then the reconfigure will
also cause a failover since it will temporarily suspend the master's operation while the
Chapter 2: Management and Maintenance
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