Wednesday, September 15, 2010

Lync 2010 and Multiple Locations with Same IP Subnet

One question users keep asking me about the Location Services in Lync 2010 is "What happens if I have the same IP addressing scheme at multiple locations?"

In my previous two posts, I talked about how Lync 2010 will keep track of the locations you've setup and will automatically set your location properly when you return.  So, what DOES happen when you leave the office, which gave you an IP address in the 192.168.20.0/24 subnet and you go home where you just so happen to use the exact same subnet? Will Lync 2010 just look at the subnet and assume that you're still in the office?

It turns out that Lync 2010 will gather as much information about your connection as it can when determining your actual location.  Not only will it use your IP address, but it will also use the identifier of the wireless access point you've connected to, or the switch ID, if connected via a hardline.

I tested this at home by connecting to two different wireless access points.  I first connected to my primary WAP and logged onto Lync 2010.  I dutifully entered my location information and set it as "Home".  I noted my IP address and disconnected.  I reconnected to my backup WAP and logged onto Lync 2010.  I had the same IP address as before.  Lo and behold, Lync asked me for my location information as if it were a new location.  I entered the same information as before, but with the location tag of "Home Test".

I then reconnected to my original WAP and sure enough, the location was set back to "Home".  I reconnected to the backup WAP, and my location changed to "Home Test".  The IP address remained the same on both WAPs, but Lync was obviously looking at more than just the IP address when determining my location.

So, Lync 2010 turns out to be very intelligent about how it determines your actual location.  It will use a combination of your IP address and any other information it can glean from the connection to ensure uniqueness.  Once you've been to most of your usual locations and set your location information once (even if those locations are not in your corporate network, you shouldn't have to ever manually set it again.

UPDATE: Jens Trier Rasmussen's blog provides some more detailed information about what exactly is used to uniquely determine your location:  http://blogs.technet.com/b/jenstr/archive/2010/09/17/how-can-lync-2010-distinguish-between-network-192-168-1-x-at-home-and-in-hotel-x.aspx