Is it OK to create CNAME records for a dynamic A record?

Question

Is it OK to create CNAME records for a dynamic A record?

Soar 116

In my company, they have been using A records only, whether those records are for server names or aliases. And since the best practice is to use CNAME records for aliases, I am planning to change that.

But many of those server name records are dynamic. So I am wondering if I should first make them static before replacing the aliases records with CNAME records. Or is it just fine to keep the server name records the way they are?

Note: I selected Azure DNS tag because there isn't another relevant tag. But the DNS I'm managing isn't Azure.

ChaitanyaNaykodi-MSFT 27,481 Reputation points Microsoft Employee Moderator

2023-05-01T20:59:12.6733333+00:00

@Soar

Thank you for reaching out. Since you are not using Azure DNS, I have added Windows DHCP tag to this question. Thank you!
Soar 116 Reputation points

2023-05-03T20:01:31.3633333+00:00

Hi Chaitanya,

I'm not asking about DHCP and how to configure IP addressed on server.

For more details and explanation, you can read my comments below.

I made the tag Azure DNS again.
GitaraniSharma-MSFT 50,096 Reputation points Microsoft Employee Moderator

2023-05-15T09:41:49.3866667+00:00

@Soar , as the question is not related to Azure DNS, I've removed it and added windows server and window network tags are the DNS or Domain Name System is part of windows server networking concept. Adding the correct tag helps directing the post to the dedicated expert team and to get faster resolution.
Soar 116 Reputation points

2023-05-15T20:27:57.8666667+00:00

I asked you to change your earlier wrong DHCP tag, but you didn't do. Good that when I re-tagged it back, you came up with something that makes sense.

To me, Azure DNS is also DNS, and the best practices of DNS apply to it. And that's the subject of my question. But I'll keep your tags.

4 answers

Your answer

ChaitanyaNaykodi-MSFT 27,481 Reputation points Microsoft Employee Moderator

2023-05-01T20:59:12.6733333+00:00

@Soar

Thank you for reaching out. Since you are not using Azure DNS, I have added Windows DHCP tag to this question. Thank you!
Soar 116 Reputation points

2023-05-03T20:01:31.3633333+00:00

Hi Chaitanya,

I'm not asking about DHCP and how to configure IP addressed on server.

For more details and explanation, you can read my comments below.

I made the tag Azure DNS again.
GitaraniSharma-MSFT 50,096 Reputation points Microsoft Employee Moderator

2023-05-15T09:41:49.3866667+00:00

@Soar , as the question is not related to Azure DNS, I've removed it and added windows server and window network tags are the DNS or Domain Name System is part of windows server networking concept. Adding the correct tag helps directing the post to the dedicated expert team and to get faster resolution.
Soar 116 Reputation points

2023-05-15T20:27:57.8666667+00:00

I asked you to change your earlier wrong DHCP tag, but you didn't do. Good that when I re-tagged it back, you came up with something that makes sense.

To me, Azure DNS is also DNS, and the best practices of DNS apply to it. And that's the subject of my question. But I'll keep your tags.

Answer 1

DF 11

Hi Soar,

Let me first make sure I understand your question correctly.

Currently, in your non-Azure DNS, you have resources that use static IP with A records and you have alias names for the same resources that also use A records, i.e.

ServerName1.yourdomain.com = IP1_address (A record)
ServerName1Alias.yourdomain.com = IP1_address (A record)

Ad you would like to make sure the alias names use CNAME records, so

ServerName1.yourdomain.com = IP1_address (A record)
ServerName1Alias.yourdomain.com = ServerName1.yourdomain.com (CNAME record)

I also understand that your concern is that some of the ServerName1 A records point to dynamically set IP addresses.

If so, you are OK to change all records for ServerNameAlias(es) from A to CNAME records. This will work fine with both static and dynamic IP addresses assigned to ServerName (A records).

As a general rule, your static network infrastructure should be using static IP addresses (so that it doesn’t rely on DHCP service, makes it more robust). In some scenarios however, it is OK to use dynamic IP addresses and DHCP to simplify devices management (i.e. printers). For those scenarios it helps to configure your DHCP to register devices in DNS automatically.

Hope this helps!

Soar 116 Reputation points

2023-04-30T12:41:01.2733333+00:00

Hi DF,

All servers do use static IP addresses. No DHCP IP configuration exists on any server (to the best of my knowledge).

The dynamic thing however is their records on the DNS. That means my predecessor didn't manually create those records on the DNS, but the DNS automatically created them as it did and is still doing the PCs' records.

So my question is: should I first create manual A records for the server names before creating CNAME records for the aliases?
DF 11 Reputation points

2023-05-04T16:24:33.6133333+00:00

Hey Soar,

I get your question now and the answer is: yes, servers with static IP addresses should be using static DNS name.

A note: as you know the dynamic DNS records are created by the DHCP service on the client, so it is interesting to see that even though your server IPs are configured as static the DNS records are dynamic. Is the timestamp on them up to date? If not (the records are stale) then this is definitely a reason to replace them with static.

Hope this helps!

Cheers
Soar 116 Reputation points

2023-05-08T19:57:52.3666667+00:00

I've read in more than a place that servers can have dynamic DNS records regardless of their static IP configuration. They say that the DNS record type only matters for aging and scavenging purposes. But maybe you're right.

My servers timestamp varies from one server to another. And as of today, they go back to up to April 24.
DF 11 Reputation points

2023-05-12T10:50:34.81+00:00
Hi @Soar,

Correct, there is nothing stopping you from creating both static and dynamic A resource records (RR) in DNS for the same network resource (i.e., server). DNS will allow it, sure. However, in general, you wouldn’t want to have multiple A RR for the same resource, especially that some would be updated automatically (dynamic RR) and others manually (static RR). This is basically a messy design, prone to errors and requiring unnecessary maintenance.

The best practise for network resources, especially those accessed by users directly, is to configure them with static IP settings. There are many reasons for doing it, but basically it makes the resource more robust for the accessing it users. Technically, however, there is nothing stopping you from configuring a server to use DHCP (rather than a static IP). It would still work, but it wouldn’t be as robust.

Best practise:

Configure network resource with static_IP and create static A RR in DNS for the resource’s main name i.e., for a server name Srv01:

Srv01.your.domain A static_IP

Create alias records (CNAME RR) for names of apps or services run on the server, pointing to the same A RR i.e., the server hosts two apps: app01 and app02 (and the apps run on the same IP as the server):

app01.your.domain CNAME Srv01.your.domain
app02.your.domain CNAME Srv01.your.domain

As you know DHCP service has been invented to automate the process of configuring node’s IP settings when it joins a network. When a server is configured to use DHCP, the DHCP client on the server finds a near DHCP server, requests an IP and registers that IP, in DNS service against the server’s name. It is that DHCP client that sets the timestamp on a dynamic RR as well and updates it every time DHCP lease is renewed. When server’s IP config changes from DHCP to static IP, the DHCP client stops being involved in IP configuration and DNS is not updated anymore.

Does 24 April correlate with the date the IP config changed to static?

Hope this helps!

Answer 2

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Answer 4

Soar 116

I don't know why you keep talking about DHCP after I explained that all the server are configure with static IP addresses. But I think now I know what to do.

I'm going to keep the existing dynamic DNS records dynamic. And then wherever I add a new Windows server, I'll let it create its own dynamic record in the DNS.

And for aliases, I'll do CNAME records regardless of what their A records are.

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Is it OK to create CNAME records for a dynamic A record?

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