How the Appliance Formulates Subsequent DNS Queries

If the DNS name server can't resolve the query, the appliance formulates subsequent DNS queries based on the information in its DNSINFO.CFG file:

The DNSINFO.CFG File

The DNSINFO.CFG file lets you control the processing of partial host names. It contains three sections:

• Domain: The <DOMAIN> keyword instructs the DNS name resolver to try appending the appliance's domain and subdomain names first. You can prevent this initial lookup sequence by removing the <DOMAIN> keyword from the file.

• DNSPingHost: The DNSPingHost keyword is an optional entry that specifies the domain that Excelerator uses to validate communications with its DNS servers.

  If multiple entries exist, Excelerator uses only the first. If no entry exists, the system uses www.volera.com by default. This entry is only used to verify the DNS server's availability. It is skipped by the name resolution process.

• Format strings: These strings give the DNS name resolver alternate names to try.

An Example

For example, assume the following:

• The browser request URL is webserver.
• The appliance's domain name is support.acme_ex2.com.
• The appliance's DNSINFO.CFG file has the following content:

  <DOMAIN>

  DNSPingHost=www.volera.com

  www.%s.com

  www.%s.ed

  www.%s.org

  www.%s.gov

  www.%s.net

  %s.com

  %s.edu

  %s.org

  %s.gov

  %s.net

  www.%s

After the initial request fails, the appliance formulates subsequent requests as follows:

1. If the <DOMAIN> keyword is not found, the process skips to Step 3. Otherwise, the appliance formulates a second query by appending the appliance's domain name to the URL as follows:

   webserver.support.acme_ex2.com

2. If this query fails, the appliance appends the appliance's subdomain names to the URL in order as follows:

   webserver.acme_ex2.com

   and then

   webserver.com

   If both these queries fail to return an IP address, the appliance continues with Step3.

3. The appliance skips the DNSPingHost entry and then appends each format string in the DNSINFO.CFG file in the order listed until one of the following occurs:
   • The DNS server returns an IP address for the name.
   • The appliance's query options are exhausted and it returns a DNS error to the browser.

4. If a DNS name has already been tried, the appliance skips the query and moves to the next item in the list.

   Continuing with the example, the appliance would submit the following queries, substituting webserver for the %s variable in the format strings of the DNSINFO.CFG file.

   www.webserver.com

   www.webserver.edu

   www.webserver.org

   www.webserver.gov

   www.webserver.net

   webserver.edu

   webserver.org

   webserver.gov

   webserver.net

   www.webserver

   Because webserver.com was tried previously, the appliance skips the sixth line (%s.com) in the DNSINFO.CFG file.