[Operators] about srv record

Dave Cridland dave at cridland.net
Tue Aug 16 09:40:23 UTC 2011


On Tue Aug 16 09:47:35 2011, Kevin Smith wrote:
> On Mon, Aug 15, 2011 at 8:44 AM, Dave Cridland <dave at cridland.net>  
> wrote:
> > On Sat Aug 13 23:34:56 2011, Josemar Müller Lohn wrote:
> >>> Is it valid to so:
> >>> _xmpp-client._tcp.alice.com. CNAME _xmpp-client.bob.com.
> >>
> >> You can only get a CNAME answer when you ask for an A record.
> >
> > I don't think that's true.
> >
> > I think it may well choke the resolvers in many XMPP  
> implementations, mind,
> > but I think it ought to work according to the specifications. A  
> CNAME merely
> > states to restart the resolution using the new name.
> >
> > Specifically, the requirement that a name with a CNAME record  
> MUST NOT have
> > any other records (aside from certain DNSSEC ones) would appear  
> to support
> > that.
> 
> Is this true? My understanding was that the target for an SRV record
> explicitly could not be a CNAME, and that the lookup done by XMPP  
> was
> explicitly SRV. (That is: I don't believe it's valid)

The RHS of a SRV cannot have a CNAME record, but I think a SRV lookup  
can legitimately return a CNAME.

So:

_xmpp-client._tcp.alice.com. CNAME _xmpp-client._tcp.bob.com.
_xmpp-client._tcp.bob.com. SRV 1 0 5222 xmpp.bob.com.

Is legal, whereas:

_xmpp-client._tcp.alice.com. SRV 1 0 522 xmpp.alice.com.
xmpp.alice.com. CNAME xmpp.bob.com.

Is not.

Dave.
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