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In this lecture we’re going to answer the question What is Recursion? We’re going take a look at the reasons why you would enable or disable recursion.
So what is Recursion?
Here is an example:
If a user opens his WEB browser and types www.serveradademy.com if the clients computer doesn’t know about serveradademy.com the DNS client will ask the preferred DNS server. let’s take a look at this clients TCPIP properties, notice the Preferred DNS servers IP address.
If the preferred server or in this case the ISP’s DNS doesn’t know about serveradademy.com, it will make queries to other DNS servers out on the internet.
This asking on behalf of the client continues until the server that is authoritative for serveradademy.com is found, and then the IP address for serveradademy.com is sent back along the chain and ends up on the clients computer. This process is known as recursion.
- Notice if you check Disable recursion notice that also disables forwarders.
- What this means is, if you only want your DNS server to answer queries based upon what it knows then check disable recursion.
In some cases, enabling recursion can be a security issue because your servers are always going out to the internet trying to resolve queries on behalf of clients. And other servers could be using your server to resolve their queries.
To disable recursion – From your DNS server Open Server Manager
- Now from tools, click the DNS manager. Right click the DNS server, from Servers properties, click the Advanced tab, and here you can disable recursion.
- Click the root hints tab. Under the Root Hints, remove all these root servers.
- If you start having problems and you need to put back all your root servers. You can use copy from server. Just type the IP address or the name of the DNS server and click ok.
- On a production DNS server, I wouldn’t disable Recursion or delete my Root Hints servers unless you have a good reason to do so.
Why you would you want to disable recursion?
- Security reasons. You are using a secure connection and don’t need DNS to go out to the Internet to resolve your queries.
- If you disable recursion there could be application problems. Emails sent from local apps may not be delivered.
- If you disable Recursion your server would only be able to answer queries based upon what it knows.
So, is there another Solution?
- One solution could be to configure selective recursion using a split-brain DNS Policy. We will discuss this when we get to policies.
- Basically, you could setup a policy that says that internal clients can query for internet names, but external clients can’t use your DNS to query for internet names. In other word’s recursion would only be allowed by internal clients and not external clients. We’ll explain more when we get into policies.
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