Port 3268 TCP UDP
Microsoft Global Catalog (LDAP) Service.
MSFT-GC is Microsoft (MSFT) Global Catalog (GC)
An LDAP service which contains data from Active Directory (AD) forests, and is also a Domain Controller (DC). These Global Catalog servers are Domain Controllers (DC's) which store additional infomration for all of the objects that exist within an AD forest.
Assuming you're within an infrastructure that has AD, you can query the SRV records of the domain (whatportis.com in this example) to find all of the Global Catalog servers - The NSlookup command for example would be:
21 Position 1 Contributor 23,282 Views
External Links: Microsoft TechNet