This article explains how to change the MAC address of a physical network adapter on an VmWare ESXi 5.1 host.
1) Connect you with SSH to your ESXi Server
2) Open the file /etc/vmware/esx.conf
3) Search for your old MAC address and replace it with the new one. You can search in the VI editor by typing “/” without brackets.
4) Save your changes by typing :wq
If you are using Xen and get an error Device xxxxx (xxx) could not be connected. Failed to find an unused loop device when you try to create a guest. This is because you are out of loop devices.
Run this on command line:
echo "options loop max_loop=32" > /etc/modprobe.d/xen
With the value 32 you are able to run 16 Guests on your host, assuming you aren’t using loop devices for other purposes. Use a number suitable for your needs.
Shutdown your guests and run this on command line:
rmmod loop && modprobe loop
Show all loop devices:
ls -l /dev/ | grep loop