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MAC Addresses used by the Cisco 3750


The CPU on a 3560 or 3750 has a stash of 128 MAC addresses allocated when the device is built, for physical ports and SVI (vlan) interfaces.

Explanation of MAC Address allocation

You can get the "base" MAC address by issueing a show version. The first 64 addresses (inclusive) from that address are used for physical ports. The next 64 after that are used for SVI (vlan) interfaces.

The CPU allocates MAC addresses to vlan interfaces in the order which the interfaces are created, so they can change after a reboot of the switch.

If you use more than 64 vlan interfaces, the additional interfaces will all get the same MAC address as the 64th interface.

For example:

base address: xx:xx:xx:xx:3e:00

first vlan address: xx:xx:xx:xx:3e:40 (this is base + 64)
last vlan address: xx:xx:xx:xx:3e:7f (this is base + 127)

Further Information

You might also find the following page interesting: Supported Platforms for Unique MAC Address Configuration on VLAN or L3 Interfaces for Catalyst Switches

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‎06-11-2009 04:31 AM
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