Unique Shared Mac Addresses - D-Link NetDefendOS User Manual

The lower number on the left in this output is the current number of connections and the higher
number on the right is the maximum number of connections allowed by the license.
The following points are also relevant to cluster setup:
• If this is not the first cluster in a network then the Cluster ID must be changed for the cluster
so that it is unique (the default value is 0). The Cluster ID determines that the MAC address for
the cluster is unique.
• Enabling the advanced setting Use Unique Share MAC is recommended so that each interface
has its own MAC address. If this is not enabled, interfaces share a MAC address and this can
confuse some third party switches.
• Make sure that the advanced setting High Buffers (found in System > Advanced Settings >
Misc. Settings in the Web Interface) is set to be automatic for both units in the cluster. This
setting determines how memory is allocated by NetDefendOS for handling increasing
numbers of connections. A NetDefendOS restart is required for a change in this setting to
take effect and this can be achieved with the CLI command:
gw-world:/> shutdown
Where a cluster has a very high number (for example, tens of thousands) of simultaneous
connections then it may be necessary to set a high value for this instead of enabling the
Dynamic High Buffers option. A very high value for High Buffers can suit situations with large
numbers of connections but can have the disadvantage of increasing throughput.
See Section 13.10, "Miscellaneous Settings" for a full explanation of these settings.

11.3.5. Unique Shared Mac Addresses

For HA setup, NetDefendOS provides the advanced option Use Unique Shared MAC Address. By
default, this is enabled and in most configurations it should not need to be disabled.
Enabling a Unique Shared MAC Address
The effect of enabling this setting is that a single, unique MAC address will be used for each pair
of matching hardware interfaces so that, for example, the lan1 interface on the master unit will
appear to have the same MAC address as the lan1 interface on the slave unit.
Problem Diagnosis
An HA cluster will function if this setting is disabled but can cause problems with a limited
number of switch types where the switch uses a shared ARP table. Such problems can be hard to
diagnose which is why it is best to always have the setting enabled.
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Chapter 11: High Availability