DNS Record Types

PTR Record

Pointer records are used to map a network interface (IP) to a host name. These are primarily used for reverse DNS.

  • Name: This usually represents the last octet of the IP address.
  • System (PTR to): This will be the value (the reverse DNS) for your host / computer within your domain.
  • TTL: The TTL (Time to Live) is the amount of time your record will stay in cache on systems requesting your record (resolving nameservers, browsers, etc.). The TTL is set in seconds, so 60 is one minute, 1800 is 30 minutes, etc.
  • Best Practice Tip
    If you plan on changing your reverse DNS TTL to a low value a few hours before you make the change (especially for mail servers). This way you won’t have any downtime during the change. Once your reverse DNS changes you can always raise your TTL to a higher value again.

 

Reverse DNS overview:

Reverse DNS is setup very similar to how normal (forward) DNS is setup.  When you delegate forward DNS the owner of the domain tell the registrar to have your domain use certain name servers.  Reverse DNS works the same way in that the owner of the IPs needs to delegate the reverse DNS to DNS Made Easy name servers as well.  The owner of the IPs is usually the ISP, the hosting provider, or your own group of they are directly delegated from ARIN.

For reverse DNS you will have to setup your reverse DNS domain.  This is a special domain that ends with “in-addr.arpa”.  This domain is created in DNS Made Easy in the same manner as any other domain (Add Domains).  You will need to ask the organization that owns those IPs (usually your ISP or your hosting provider) what domain name to create as it is based on how large of a block of IPs you have and how they are delegated to your group.

Then you will have to have the organization that owns those IPs (usually your ISP or hosting provider) delegate the reverse DNS for your IPs to DNS Made Easy (similar to how you delegated the DNS for your domains to DNS Made Easy).

If you only have a few hosts that you need reverse DNS for, it may be easier to just have the owner of those IPs set the entries in their reverse DNS domain for your hosts.

We have a full step by step tutorial that you can view at:

http://help.dnsmadeeasy.com/spry_menu/how-to-setup-reverse-dns/

 

Example 1 – PTR record for the 192.168.1.0/27 block (addresses 192.168.1.1 – 192.168.1.30) and the reverse DNS for 192.168.1.10.  This PTR record is created in the “27/1.168.192.in-addr.arpa” zone.

NAME TTL TYPE DATA/SYSTEM
10.27/1.168.192.in-addr.arpa. 1800 PTR mail.example.com.

Configuration:

1

PTR record details:

  • Name: 10.27/1.168.192.in-addr.arpa. is the host which are we are making an entry for.  The domain / zone name is always appended to your domain.  So in the data entry screen we only enter 10. The format of your reverse zone is dependent on how your provider delegates it, for example our ISP could have used 27-1.168.192.in-addr.arpa. instead of 27/1.168.192.in-addr.arpa. You must ask your provider for the correct syntax of your zone as reverse DNS will not resolve unless this is set up in the same syntax as the delegation. 
  • Data / System : mail.example.com. (including the trailing dot). You must include the trailing dot to keep the reverse DNS domain name from being appended to the end of your record.
  • TTL (time to live) – The 1800 indicates how often (in seconds) that this record will exist (will be cached) in other systems.
  • The end result of this record is that 10.27/1.168.192.in-addr.arpa. points to mail.example.com.