Alibaba Cloud DNS:Reverse DNS lookups and PTR records

What is a reverse DNS lookup

Multiple domain names can use the same IP address. A reverse DNS lookup finds the domain name associated with an IP address. However, traversing the entire DNS system to find a matching domain name for an IP address is not feasible. To solve this problem, RFC 1035 defines the Pointer (PTR) record. A PTR record maps an IP address to a domain name.

Configuration flow

1. Create a reverse lookup zone for the IP address network.

2. Add a PTR record to the reverse lookup zone.

For example, if your network address range is 192.168.0.1-192.168.0.255, which is part of the 192.168.0.0/24 class C IP address range, the corresponding reverse lookup zone is 0.168.192.in-addr.arpa. If you add a PTR record for host 1 in the zone 0.168.192.in-addr.arpa that points to www.example.com, a reverse DNS lookup for the IP address 192.168.0.1 resolves to www.example.com.

In a private network environment, you can manage the following reserved address ranges and create reverse lookup zones.

• 10.0.0.0 - 10.255.255.255

• 172.16.0.0 - 172.31.255.255

• 192.168.0.0 - 192.168.255.255

Add a PTR record in internal DNS

Follow these steps to add a reverse lookup domain (zone) for the 192.168.1.0/24 address range:

1. Go to Alibaba Cloud DNS - Private DNS.

2. On the Authoritative Zone page, select the User Defined Zones tab and click Add Zone.

3. In the Authoritative Zone field, enter 1.168.192.in-addr.arpa and submit the form.

   

4. On the User Defined Zones tab, find the newly added built-in authoritative domain, and in the Actions column, click Settings.

5. Click Add Record. Add a PTR record, set the host to 1, and point the record to the host host001.example.com.

   

6. Submit the form.

Set the scope

1. On the User Defined Zones tab, find the target domain name. In the Actions column, click the Effective Scope button and select a VPC.