Hi,
The MAC address table size is based on the sup for the 6500 series. Here are some numbers for Sup 2T.
In the legacy compute environment, one physical server runs one application and has a single active connection to the access layer. At the aggregation layer, each switch has only half of its interfaces active (most likely 10 Gigabit Ethernet in a data center architecture) as a result of Hot Standby Router Protocol (HSRP) and Spanning Tree Protocol (STP) operations. Since there are no virtual machines (VMs) running in this environment, the maximum number of MAC addresses required at the distribution layer is roughly:
Maximum 10G density = 130 ports (6509-E with 8 x WS-X6716-10G-3C/3CXL)
Maximum 10G Density density with HSRP/STP operations: 65
Maximum 1G density at access layer = 384 ports (8 x WS-X6748-GE-TX)
Number of MAC addresses per 1G host = 1
Maximum number of MAC addresses at distribution = (65 * 384 * 1) = 24,576
In the virtualized compute environment, each physical server runs multiple VMs and has multiple active connections to the access layer because of the Cisco Catalyst 6500 Series Virtual Switching System (VSS). At the distribution layer, each switch has all of its interfaces active as a result of VSS. The maximum number of MAC addresses dictates the total number of VMs that can be supported in a pod connecting to a VSS. With a table size of 128 K, the PFC4 can support up to 42,666 VMs since each VM has three MACs each - one for each network interface card (NIC) and one for server migration (for example, through VMware vMotion). This is an increase of over 10,000 VMs compared to what the PFC3 could support (32,000).
Link:
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/white_paper_c11-663636.html
HTH
