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Configuring Communicator Web Access DNS Records

Communications Server 2007 R2

Topic Last Modified: 2009-01-23

Like most networked-aware applications, Communicator Web Access (2007 R2 release) relies on Domain Name System (DNS) records to map URLs (for example, https://im.contoso.com) to a computer (or, in some cases, pool of computers). To support Communicator Web Access you need to create two types of DNS records:

  • Host name records. (also known as an A record or AAAA record). A host name record maps the fully qualified domain name (FQDN) of the computer (for example, im.contoso.com) to an IP address.
  • Canonical name (CNAME) records. CNAME records enable you to refer to the same computer (and the same IP address) in multiple ways. Thus, as.im.contoso.com, download.im.contoso.com, and im.contoso.com can all refer to the same physical computer.

The records you need to create depend on how you are deploying Communicator Web Access. In general, you will always need a host record for each computer or load balancer you have deployed. In addition, you need to create CNAME records named as and downloaded in order to support desktop sharing.

Following are some common Communicator Web Access scenarios along with the required DNS records.

In some cases you might have just one Communicator Web Access computer (for example, a server named im, with the fully qualified domain name (FQDN) im.contoso.com). If you intend to use the URL https://im.contoso.com in order to access Communicator Web Access that means that the Communicator Web Access URL and the computer’s fully qualified domain name are the same.

Under this scenario you need to create the following DNS records:

  • A host name record for the Communicator Web Access URL (im.contoso.com)
  • A CNAME record, download.im.contoso.com
  • A CNAME record, as.im.contoso.com

In many cases the Communicator Web Access URL and the fully qualified domain name (FQDN) of the Communicator Web Access computer will not match. For example, suppose the computer is named cwaserver.contoso.com, but you would like the Communicator Web Access URL to be https://im.contoso.com. In a case like this you need to create an additional CNAME record, one that maps im.contoso.com to cwaserver.contoso.com.

Under this scenario you need to create the following DNS records:

  • A host name record for the desired URL (im.contoso.com)
  • A CNAME record, download.im.contoso.com
  • A CNAME record, as.im.contoso.com

Note that the as and download records should reference the Communicator Web Access URL rather than the fully qualified domain name (FQDN) of the server.

If you are using a hardware load balancer, then your CNAME records (as and download) must refer to the IP address of the load balancer rather than the IP address of an individual Communicator Web Access server. In this case, you will also need to create a host name record for the load balancer.

Under this scenario you need to create the following DNS records:

  • A host name record for the desired URL (im.contoso.com)
  • A CNAME record, download.im.contoso.com
  • A CNAME record, as.im.contoso.com

The CNAME records should all point to the IP address of the load balancer rather than to the IP address to any of the computers.

A similar approach is required if you are using a reverse proxy server to handle external traffic and logons. In that case, your CNAME records must refer to the IP address of the reverse proxy server. You will also need to create a host name record for this server.

Under this scenario you need to create the following DNS records:

  • A host name record for the desired URL (im.contoso.com)
  • A CNAME record, download.im.contoso.com
  • A CNAME record, as.im.contoso.com

The CNAME records should all point to the reverse proxy server rather than to either of the computers. All DNS records that point to the reverse proxy server must be located in a DNS server that is publicly available.

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