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

[ktm at rice.edu]

On Sat, May 05, 2012 at 09:00:00AM +0200, Thomas Faddegon wrote:
> 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


Hi Thomas,

Based on the RFC, if you have a CNAME record, you cannot have ANY other
record with that name. That is just the way it works.

Ken