VoIP severs requiring the use of "virtual MAC address" configuration.  For this article the VoIP server tested supports three Ethernet ports. Each port has one signaling and one bearer IP.  The signalling IP MAC addresses are all unique, however, the MAC address for each of the 3 bearer IP's are the same.

3 Signalling IP's = Each IP/MAC address is unique
3 Bearer IP's = 1 MAC address for all IP's

The VoIP server board has 3 Ethernet ports.  Each port has one signaling and one bearer IP.  The MAC address for each signaling IP is distinct and unique. However, the MAC address for each of the 3 bearer IP's is the same.  The same MAC is configured, or used, for each of the bearer IP's and all ports are made part of the same vlan, MAC re-learning leads to packet flooding on any switch port set as trunk or member of the same VLAN.

To avoid fast MAC re-learning which leads to packet flooding it is recomended having each of the VoIP server interfaces in seperate VLANs.  This has been tested and confirmed to work in this type of VoIP server deployment where you have to configure a "virtual MAC address" for each of the bearer IP's.