Split DNS! What is it and when should you use it? Split DNS is a method of splitting (duh!) your DNS zone when you use the same domain name for your internal and external domains.

In an unsplit DNS setup, you have a single DNS zone for domain.com. All the resource records for internal and external servers are included in one zone. You publish your DNS servers to the external network so that external clients can access your published servers. In this type of setup your DNS zone would be setup as follows:

• domain.com www A 111.222.111.1
• mail A 111.222.111.2
• web A 192.168.1.101
• exch A 192.168.1.102       
• MX mail.domain.com

With a split DNS configuration you have two dns zones setup, an internal zone with the internal records for your local clients on an internal DNS server and an external zone on an external server with the external records to be used by your external clients. Most domain registrars offer some type of DNS service which you can use for the external zone. In this setup your DNS zones would look like this.

External domain.com

• www A 111.222.111.1
• mail A 111.222.111.2       
• MX mail.domain.com

Internal domain.com

• www CNAME web.domain.com
• mail CNAME exch.domain.com
• web A 192.168.1.101
• exch A 192.168.1.102

For more DNS tips see:

DNS Tips