Using Unique Shared Mac Addresses - D-Link NetDefend DFL-210 User Manual

11.3.4. Using Unique Shared Mac
Addresses
• Make sure that the advanced setting High Buffers 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 hardware restart is required for a change in this setting to
take effect.
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 using automatic. A
very high value for High Buffers can suit situations with large numbers of connections but can
have the disadvantage of increasing throughput latency.

11.3.4. Using 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. 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.
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.
In one situation, this setting should be disabled and that is when an HA cluster is set up using
non-matching hardware. In order to function correctly, unique shared MAC addresses should not be
used.
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Chapter 11. High Availability