What is Partial zone transfer (IXFR)?

The Partial zone transfer (IXFR) is an exciting process, which in some cases it is very valuable. So, let’s explain a little bit more about it.

Zone transfer – definition

The zone transfer process includes duplicating the DNS data with all of the DNS records from the Primary DNS zone to the Secondary DNS zones. Thanks to it, you could create copies of all of your DNS data into one or several name servers. That way, you improve the availability of your domain name. In addition, you make sure that even if one of the name servers is down for some reason, your website is still going to be reachable for your clients. Besides, if you own an international website, the DNS resolution process is going to be quicker, for sure. The reason for that is the DNS data is going to be stored in more than one point of presence (PoP).

Partial zone transfer (IXFR)

The Partial zone transfer, or also known as IXFR zone transfer, gives you the opportunity to duplicate only the new modifications and adjustments from the Master DNS zone to the Secondary DNS zone.

When you don’t want to make a copy of the entire collection of DNS records, the IXFR zone transfer is the perfect solution. For instance, you can use it when you have adjusted just a few DNS records, like adding one new A record, and everything else is the same.

The Secondary DNS server is capable of pulling the new information. In addition, it could be arranged to check periodically after some period of time for new changes in the Master. For that purpose, it compares the serial numbers of the SOA record. In cases when this number has changed, the Secondary is going to obtain the new modifications from the Master DNS server. 

A different way for getting the new data is by getting a notification (DNS NOTIFY) from the Master DNS server, which tells that there is a modification. Then, the Secondary DNS server requests for the modifications, and if they have permission, they are going to obtain the new DNS data. 

As you see, the Partial zone transfer (IXFR) demands less data transfer which makes it a very practical and efficient approach.

Partial zone transfer vs. Full zone transfer

When we are comparing the two different types of zone transfer – the Partial zone transfer (IXFR) and the Full zone transfer (AXFR zone transfer) we could spot the difference instantly. 

The Full zone transfer includes duplicating the whole collection of available DNS records from the Primary DNS zone to the Secondary DNS zone. It is typically used when you deploy a new name server or when you haven’t updated the changes to the Secondary for a while.

Partial zone transfer (IXFR) is used only in cases when you have added, deleted, or modified several DNS records. The advantage is that you use less bandwidth, and you are not duplicating the entire zone file. 

Author: isabella

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