Static or dynamic mac address

[ted185]

I have a virtual web server running under windows 2008R2 using hyper-v.
The Hyper-V servers is part of a clustered pair.

Every week the server is set to re-boot. Every so often the ip address
for that server becomes un-reachable.

If the WEB server moves from one clustered Hyper-V server to another the MAC
address is getting chagned.

Access to this server is through a cisco PIX firewall.

Should I set up the virtual WEB server to use a static mac address? It
looks like the day that I had issues accessing the web server the mac address
had changed.

Ted