[Pdns-users] Empty CNAME will result "server can't find: NXDOMAIN"

[Thomas Faddegon]

Hi PDNS community,

I want implement empty CNAME records instead of empty A records in our DNS
environment. But when I implement the empty records my MX records won't
work anymore.

Example:

*nslookup
> set type=mx
> set debug
> online-engineers.nl
Server: 212.54.40.25
Address: 212.54.40.25#53

------------
    QUESTIONS:
        online-engineers.nl, type = MX, class = IN
    ANSWERS:
    ->  online-engineers.nl
        mail exchanger = 20 mx2.global-e.nl.
        ttl = 120
    ->  online-engineers.nl
        mail exchanger = 50 mx3.global-e.nl.
        ttl = 120
    ->  online-engineers.nl
        mail exchanger = 20 mx1.global-e.nl.
        ttl = 120
    AUTHORITY RECORDS:
    ADDITIONAL RECORDS:
------------
Non-authoritative answer:
online-engineers.nl mail exchanger = 20 mx2.global-e.nl.
online-engineers.nl mail exchanger = 50 mx3.global-e.nl.
online-engineers.nl mail exchanger = 20 mx1.global-e.nl.

Authoritative answers can be found from:

*

Then I add an empty CNAME: online-engineers.nl CNAME some.otherdomain.nl

And I start a new nslookup:
*
> online-engineers.nl
Server: 212.54.40.25
Address: 212.54.40.25#53

------------
    QUESTIONS:
        online-engineers.nl, type = MX, class = IN
    ANSWERS:
    ->  online-engineers.nl
        canonical name = some.otherdomain.nl.
        ttl = 86400
    AUTHORITY RECORDS:
    ->  nl
        origin = ns1.dns.nl
        mail addr = hostmaster.domain-registry.nl
        serial = 2012050309
        refresh = 7200
        retry = 900
        expire = 2419200
        minimum = 900
        ttl = 900
    ADDITIONAL RECORDS:
------------
** server can't find online-engineers.nl: NXDOMAIN
Server: 212.54.40.25
Address: 212.54.40.25#53

------------
    QUESTIONS:
        online-engineers.nl, type = MX, class = IN
    ANSWERS:
    ->  online-engineers.nl
        canonical name = some.otherdomain.nl.
        ttl = 86400
    AUTHORITY RECORDS:
    ->  nl
        origin = ns1.dns.nl
        mail addr = hostmaster.domain-registry.nl
        serial = 2012050309
        refresh = 7200
        retry = 900
        expire = 2419200
        minimum = 900
        ttl = 900
    ADDITIONAL RECORDS:
------------
** server can't find online-engineers.nl: NXDOMAIN
>
>
> *

And when I remove the empty CNAME everything works fine again:
*
> online-engineers.nl
Server: 212.54.40.25
Address: 212.54.40.25#53

------------
    QUESTIONS:
        online-engineers.nl, type = MX, class = IN
    ANSWERS:
    ->  online-engineers.nl
        mail exchanger = 50 mx3.global-e.nl.
        ttl = 120
    ->  online-engineers.nl
        mail exchanger = 20 mx1.global-e.nl.
        ttl = 120
    ->  online-engineers.nl
        mail exchanger = 20 mx2.global-e.nl.
        ttl = 120
    AUTHORITY RECORDS:
    ADDITIONAL RECORDS:
------------
Non-authoritative answer:
online-engineers.nl mail exchanger = 50 mx3.global-e.nl.
online-engineers.nl mail exchanger = 20 mx1.global-e.nl.
online-engineers.nl mail exchanger = 20 mx2.global-e.nl.

Authoritative answers can be found from:
*

Is there a way to fix this? In the past I found an article (RFC, sorry I
can't find the source anymore) that officially empty CNAME's isn't allowed
in DNS. But many companies works with empty CNAME's , even google and
amazon.

So I think there must be a way - or workaround - to fix this.

I hope someone can give me a solution.

Regards,
Thomas
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