[Freeipa-users] Correct syntax for round-robin DNS srv records

[Petr Spacek]

On 22.7.2014 00:13, Mark Heslin wrote:
> Hi All,
>
> I had some off-list exchanges with Petr Spacek on this but am still trying to
> work out the correct syntax.
> I have 2 hosts:
>
>     - foo1.example.com
>     - foo2.example.com
>
> and would like to create a round-robin DNS srv record for both called
> foo.example.com
>
> I already have DNS entries for both hosts in IPA:
>
>    # ipa dnsrecord-show example.com foo1
>      Record name: foo1
>      A record: 10.0.0.1
>    # ipa dnsrecord-show example.com foo2
>      Record name: foo2
>      A record: 10.0.0.2
>
> I'd like to get the correct syntax for adding the srv record for foo.
> My understanding is that it should be something like this:
>
>    # ipa dnsrecord-add example.com _foo.tcp --srv-rec="0 50 53 foo1.example.com"
>    Record name: _foo.tcp
>    SRV record: 0 50 53 foo1.example.com
>    # ipa dnsrecord-add example.com _foo.tcp --srv-rec="0 50 53 foo2.example.com"
>    Record name: _foo.tcp
>    SRV record: 0 50 53 foo2.example.com
>
> which seemed to be added ok but on second glance I think not:
>
>    # host -t srv _foo.tcp.example.com
>    _foo.tcp..example.com has SRV record 0 50 53 foo1.example.com.example.com.
>    _foo.tcp..example.com has SRV record 0 50 53 foo2.example.com.example.com.
>
> In looking over the description of rfc2782
> <http://en.wikipedia.org/wiki/SRV_record> it appears the IPA syntax is a
> little different,

I don't think so :-)

Please note the trailing dot in "target" part of 
http://en.wikipedia.org/wiki/SRV_record#Record_format.

IPA behaves in the same way as BIND 9: All domain names without trailing dot 
are automatically extended with zone origin, i.e. "example.com.".

You have two options:
# ipa dnsrecord-add example.com _foo.tcp --srv-rec="0 50 53 foo1" (DNS server 
will automatically append "example.com.")

or

# ipa dnsrecord-add example.com _foo.tcp --srv-rec="0 50 53 foo1.example.com."
(please note the trailing dot)



Another note is about "_foo". "foo" should be "service name" according to
http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml

It will probably not cause any problems if you invent your own name 
(preferably prefixed with x- to avoid collisions in future, e.g. "_x-foo"), 
but it will not hurt you if you register your protocol into the registry :-)
See http://tools.ietf.org/html/rfc6335

> and the documentation is scarce so admittedly I'm taking a swag at this ;-)
>
> I can do this fine without srv but don't have enough familiarity with DNS srv
> here.
> Can anyone help clarify what I'm missing? I'd like to have equal weighting,
> priority
> to both hosts - I'm assuming the port (53) is correct for DNS here as well.
What are you trying to achieve? The port number refers to port used by your 
application, not to DNS.

-- 
Petr^2 Spacek