Reverse DNS with BYOIP

Question

Hi there,

We have a couple of BYOIP pools we've imported into AWS and need to set up reverse DNS. For all of the IPs we allocate from that pool the "Update reverse DNS" option is disabled. The IPs have A records and the option is available for all of the other elastic IPs. Just wondering how we set up reverse DNS for these BYOIPs?

Cheers

Answer

You need to find who is the DNS authority for reverse DNS (i.e. name servers for the subnet). Ideally it's a full class C (or larger, i.e. /24) - if not it can get more complex and may eliminate option A below.

Remember DNS reads right to left, so lookup name server for 3.2.1.in-addr.arpa if your IP was 1.2.3.0/24 (i.e. 1.2.3.4 is one of your IPs).

I did a couple queries via CloudShell:

sudo apt install bind-tools -y

dig NS 3.2.1.in-addr.arpa

Once you find the authoritative name server then you can either request: a) Move it to route 53 (I've never done this but it's likely why your option is disabled) b) Request changes in the name server manually / outside of AWS

Below is a sample output, This one is managed by cais so I would have to contact them to make changes / assign the NS to Route 53 if I had the /24:

[cloudshell-user@ip-10-6-21-56 ~]$ dig NS 10.177.205.in-addr.arpa.

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.amzn2.5.2 <<>> NS 10.177.205.in-addr.arpa.

.....

;; ANSWER SECTION:

10.177.205.in-addr.arpa. 300 IN NS ns.cais.com.

10.177.205.in-addr.arpa. 300 IN NS ns2.cais.com.

You may end up with no NS entries listed, if that's the case you need to go back to whomever manages your IP addresses and ask them why there is no authoritative name server for the IP subnets.

Good luck!

Reverse DNS with BYOIP

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