Re: [DNSOP] SVCB and the specialness of _

Ben Schwartz <> Wed, 07 October 2020 01:10 UTC

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From: Ben Schwartz <>
Date: Tue, 06 Oct 2020 21:09:50 -0400
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To: Brian Dickson <>
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Subject: Re: [DNSOP] SVCB and the specialness of _
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On Tue, Oct 6, 2020 at 8:51 PM Brian Dickson <>

> Other than the syntactic brevity, is there any functional difference to
> the client between a TargetName of "." versus a TargetName of "$HOSTNAME"
> in the description above?

Currently, "." means $HOSTNAME for the HTTPS record (when no prefixes are
applied).  With the proposed change, "." would always mean $HOSTNAME when a
ServiceMode record is returned directly for the original query.  However,
if the ServiceMode record is reached via a CNAME or AliasMode record, then
"." does not correspond to (the original) $HOSTNAME.

First, is the use of the standard zone file construct of "@", which only
> exists within the zone master file, and gets substituted on import with
> whatever $ORIGIN is.

Yes, the syntax already supports "@" and relative names when writing out a
TargetName in the zone file.  This is useful, but I don't think it has the
effect of guiding users toward a good configuration.