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Microsoft Lync 2013 IIS ARR ( Application Request Routing) web server received an invalid response while acting as a gateway or proxy server

IIS (ARR) Application Request Routing enables Web server administrators, hosting providers, and Content Delivery Networks (CDNs) to increase Web application scalability and reliability through rule-based routing, client and host name affinity, load balancing of HTTP server requests, and distributed disk caching.
There are couple of ways for Microsoft Lync Reverse proxy  1. Apache Server 2. IIS ARR. You can use my Step By Step Guide to Configure Apache as a Reverse Proxy for Lync 2010 & Lync 2013 if you are interested in Apache server as reverse proxy.

Now TMG now being discontinued by Microsoft. Now most of the users are using IIS ARR or Apache as reverse proxy for Lync 2013. Here I am planning to IIS ARR (Application Request Routing) as a reverse proxy for my Lync 2013. As per Microsoft TechNet Internet Information Server Application Request Routing (IIS ARR) is a fully tested and supported option for implementing a reverse proxy for Lync Server 2010 and Lync Server 2013. Please check below TechNet article

IIS (ARR) Application Request Routing requirements,
Windows Server 2008
Windows 2008 R2
Windows Server 2012 OR Windows Server 2012 R2

You will need two NIC cards for IIS ARR, one is for external traffic with default gateway to get traffic from internet and second one for communicate with Lync 2013 front end server.

Note - Do not join reverse proxy server (IIS ARR) to your domain.

While working on IIS  (ARR) Application Request Routing) on Windows 2012 I was getting below error after digging a lot finally I found solution.

"Web server received an invalid response while acting as a gateway or proxy server"

If you are using Windows 2012 for IIS ARR then simply install ARR 3.0 from below URL, I have faced lots of issue when I used ARR 2.6 on Windows 2012, When ever I opened dialin or meet URL i was getting above errors.

Download IIS ARR 3.0

Update - Also make sure you have created host entry for meet,dialin,lyncweb & lyncdiscover on IIS ARR server. All entries should be point to the Internal IP address of the front end server.
e.g meet.vmwareandme.com ->>