Ethernet – List over assigned global Ethernet MAC multicast address

Is there a reliable way to infer the switch "Base ethernet MAC Address" from receiving such a CDP interface MAC Address, so that I can use that "Base ethernet MAC Address" as a globally unique identifier for the switch device equipment on the network?

You can't determine the base ethernet mac from CDP without guessing or assumptions about how Cisco behaves today (as well as future behavior). On the other hand, if all you want is a unique identifier, use the Chassis serial number; however, that would require polling the CDP source for entPhysicalSerialNum... a small price to eliminate guesswork.

entPhysicalSerialNum has the added bonus of working across many of Cisco's current platforms.

Sample SNMP walk of entPhysicalSerialNum:

[mpenning@tsunami ~]$ snmpbulkwalk -OXsq -v 2c -c ciscoro -m ENTITY-MIB \
  172.16.1.200 entPhysicalDescr
entPhysicalDescr[1] 2650 chassis
entPhysicalDescr[2] 2600 Chassis Slot
entPhysicalDescr[3] C2600 Mainboard
entPhysicalDescr[4] 2600 DaughterCard Slot
entPhysicalDescr[5] 2600 DaughterCard Slot
entPhysicalDescr[6] AIM Container Slot 0
entPhysicalDescr[7] 2600 Chassis Slot
entPhysicalDescr[8] One port Fastethernet TX
entPhysicalDescr[9] AmdFE
entPhysicalDescr[10] AmdFE
[mpenning@tsunami ~]$ snmpbulkwalk -OXsq -v 2c -c ciscoro -m ENTITY-MIB \
  172.16.1.200 entPhysicalSerialNum
entPhysicalSerialNum[1] JAB05290Z8Q
entPhysicalSerialNum[2]
entPhysicalSerialNum[3] yyyyyyyyyyy
entPhysicalSerialNum[4]
entPhysicalSerialNum[5]
entPhysicalSerialNum[6]
entPhysicalSerialNum[7]
entPhysicalSerialNum[8] 25809045
entPhysicalSerialNum[9]
entPhysicalSerialNum[10]
[mpenning@tsunami ~]$

I was able to resolve the issue. On the Kemp (with HA pair) you have the option of using a "Virtual MAC Address". If this box isn't checked, then the MAC of a load balancer VIP is that of the physical interface of the active Kemp unit. If this box is checked, then the MAC address of the VIP is a VRRP MAC. As you mentioned above the VRRP RFC states that the MAC being "00:00"{blah} with the last octet being the Router ID. The default Kemp HA [router] ID is 01. On my Powerconnects using Firmware 5.1.x.x I'm not using VRRP but I ran some traces and determined that the Powerconnect will drop a VRRP frame if the router ID is the same as itself. They do this EVEN if VRRP isn't configured and in that mode they default to 01. So changing the Kemp HA router ID to something like 22 (0x16) resulted in everything working.