# splitdns.config¶

The splitdns.config file enables you to specify the DNS server that Traffic Server should use for resolving hosts under specific conditions. For more information, refer to Split DNS.

To specify a DNS server, you must supply the following information in each active line within the file:

• A primary destination specifier in the form of a destination domain, a destination host, or a URL regular expression
• A set of server directives, listing one or more DNS servers with corresponding port numbers

You can also include the following optional information with each DNS server specification:

• A default domain for resolving hosts
• A search list specifying the domain search order when multiple domains are specified

After you modify the splitdns.config file, run the traffic_ctl config reload command to apply the changes.

## Format¶

Each line in the splitdns.config file uses one of the following formats:

dest_domain=dest_domain | dest_host | url_regex named=dns_server def_domain=def_domain search_list=search_list


The following list describes each field.

dest_domain
A valid domain name. This specifies that DNS server selection will be based on the destination domain. You can prefix the domain with an exclamation mark (!) to indicate the NOT logical operator.
dest_host
A valid hostname. This specifies that DNS server selection will be based on the destination host. You can prefix the host with an exclamation mark (!) to indicate the NOT logical operator.
url_regex
A valid URL regular expression. This specifies that DNS server selection will be based on a regular expression.
named

This is a required directive. It identifies the DNS server that Traffic Server should use with the given destination specifier. You can specify a port using a colon (:). If you do not specify a port, then 53 is used. Specify multiple DNS servers with spaces or semicolons (;) as separators.

You must specify the domains with IP addresses in CIDR (“dot”) notation.

def_domain
A valid domain name. This optional directive specifies the default domain name to use for resolving hosts. Only one entry is allowed. If you do not provide the default domain, the system determines its value from /etc/resolv.conf
search_list
A list of domains separated by spaces or semicolons (;). This specifies the domain search order. If you do not provide the search list, the system determines the value from resolv.conf(5)

## Examples¶

Consider the following DNS server selection specifications:

dest_domain=internal.company.com named=255.255.255.255:212 255.255.255.254 def_domain=company.com search_list=company.com company1.com
dest_domain=!internal.company.com named=255.255.255.253


Now consider the following two requests:

http://minstar.internal.company.com


This request matches the first line and therefore selects DNS server 255.255.255.255 on port 212. All resolver requests use company.com as the default domain, and company.com and company1.com as the set of domains to search first.

http://www.microsoft.com


This request matches the second line. Therefore, Traffic Server selects DNS server 255.255.255.253. Because no def_domain or search_list was supplied, Traffic Server retrieves this information from resolv.conf(5)