IPv6 automatic reverse DNS

Baldur Norddahl baldur.norddahl at gmail.com
Fri Oct 28 23:02:57 UTC 2016


Hello

Many service providers have IPv4 reverse DNS for all their IP addresses. 
If nothing is more relevant, this will often just be the IPv4 address 
hashed somehow and tagged to the ISP domain name. For some arcane reason 
it is important to have the forward DNS match the reverse DNS or some 
mail servers might reject your mails.

However with IPv6 it is not practical to build such a complete reverse 
DNS zone. You could do a star entry but that would fail the 
reverse/forward match test.

It should be simple to build a DNS server that will automatically 
generate a hostname value for every reverse lookup received, and also be 
able to parse that hostname value to return the correct IPv6 address on 
forward lookups.

Does any DNS server have that feature? Should we have it? Why not?

I know of some arguments for:

1a) mail servers like it

1b) anti spam filters believe in the magic of checking forward/reverse 
match.

2) traceroute will be nicer

3) http://ipv6-test.com/ will give me 20/20 instead of 19/20 (yes that 
was what got me going on this post)

4) Output from "who" command on Unix will look nicer (maybe).

Regards,

Baldur


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