it depends if you configure your VPN server for windows authentication you
don't needs IAS ( IAS is a radius server)
but if you configure you VPN server for radius authentication then you need
to have IAS server installed
While it is true that if your access server can use
Windows authentication this is not the only reason
for using a IAS/RADIUS server.
He may have security or other reasons for "needing"
IAS, as described below....
One typically need RADIUS (IAS) in four situations:
1) Different companies OWN the access points and the
authentication servers
2) Different vendors BUILD the access points and the
authentication servers
3) You wish to use different MACHINES so as to
separate the access from the authentication for the
purpose usually of inserting FIREWALLS between
4) You wish to consolidate the ACCESS POLICY of
many access points on a single server (RADIUS).
In #1 and #2, you are providing an open standard glue between
access servers and authenticators (AD, UNIX, etc.)
In #3, you are separating the functionality. While this could be
for performance reasons it is generally so that you can further
protect the different components with filters and firewalls since
by their nature access servers are EXPOSED.
In #4, you might have 10 access servers (even owned by the
same company and all built by Microsoft) but wish to consolidate
the "Remote Access Policy" on your single-IAS server so that
changes can be made one time and affect all access servers/clients.
Several (or even all) of the reasons may apply at the same time.