MAC address ranges of virtualized world

Nowadays when several MAC addresses are associated with one switch port, we cannot assume that this port is connected to another switch or hub as before. It might be connected to a Virtual Machine server.

It would be helpful for us to locate which switch ports are connected to Virtual Machine servers, right from command line interface.

The following table copied from Microsoft Technet site summarizes default MAC addresses information used by VMWare, Xen, and Microsoft:

Microsoft Technet: How to Set the Static MAC Address Range for Virtual Network Devices

Reserved For	Prefixes
VMware	00:05:69 00:0C:29 00:1C:14 00:50:56
Microsoft	00:03:FF 00:0D:3A 00:12:5A 00:15:5D 00:17:FA 00:1D:D8 00:50:F2
XenSource	00:16:3E

How to make use of this table? Use "show mac-address-table interface" command to check first. For example:

Switch# show mac-address-table interface f0/1
Vlan Mac Address Type Ports
---- ----------- -------- -----
100 0015.5dXX.YYYY DYNAMIC Fa0/1
100 0015.5dXX.ZZZZ DYNAMIC Fa0/1
Total Mac Addresses for this criterion: 2
Switch#


According to the show command result and above table, we are almost sure that interface "FastEthernet0/1" is connected to one Microsoft Virtual Server host.

If we change the command to "show mac-address-table | include 0015.5d" form, we can even list how many virtual guest instances are there inside your network:

Switch# show mac-address-table interface | include 0015.5d
100 0015.5dXX.YYYY DYNAMIC Fa0/1
100 0015.5dXX.ZZZZ DYNAMIC Fa0/1
200 0015.5dWW.YYYY DYNAMIC Fa0/3
200 0015.5dWW.ZZZZ DYNAMIC Fa0/4
Switch#

Welcome to virtualized world!