Technical Tip: How to setup PTR record for a specific IP

Description

This article describes how to configure a PTR record on FortiADC for reverse DNS resolution.

Before proceeding, make sure the required DNS zone configuration is available. Refer to the documentation linked at the end of this article for more information.

Scope

FortiADC and FortiADC VM.

Solution

A PTR record maps an IP address to a fully qualified domain name (FQDN). It is commonly used for reverse DNS lookups.

In this example, the following forward DNS record already exists:

mail.example.com → 10.10.0.100

The PTR record will provide the corresponding reverse lookup:

10.10.0.100 → mail.example.com

For a /24 network, create a primary reverse DNS zone using the first three octets of the IP address in reverse order, followed by in-addr.arpa.

For example:

10.10.0.100	    0.10.10.in-addr.arpa.	    100
192.168.200.20	200.168.192.in-addr.arpa.	20

In FortiADC, it is necessary to create a new Primary zone when Configuring DNS zones.

GUI configuration:

1. Go to Global Load Balance → Zone Tools → Zone.

2. Select Create New.

3. Configure the zone as follows:
   Name: 0.10.10.in-addr.arpa.
   Type: Primary
   Domain Name: 0.10.10.in-addr.arpa.

4. Under Zone Records, select Create New >> PTR Record.

5. Configure the PTR record as follows:
   PTR Address: 100
   FQDN: mail.example.com.

6. Save the configuration.
   
   

The trailing dot represents the root of the DNS namespace and ensures that the value is treated as an absolute domain name.

 

CLI configuration:

config global-dns-server zone
    edit "0.10.10.in-addr.arpa."
        set domain-name 0.10.10.in-addr.arpa.
            config ptr-record
                edit 1
                    set ptr-address 100
                    set fqdn mail.example.com.
                next
            end
        end
    end

Verification:

Use nslookup or dig to perform a reverse lookup:

fn nslookup 10.10.0.100

The result should show that 10.10.0.100 resolves to mail.example.com.

Refer to this document for more information on configuring the DNS zone: Configuring DNS zones.