[bind10-dev] IXFR to AXFR fallback (Re: b10-xfrin fails to receive IXFR while b10-xfrout is processing AXFR)

[JINMEI Tatuya / 神明達哉]

At Mon, 29 Apr 2013 09:01:19 +0200,
Michal 'vorner' Vaner <michal.vaner at nic.cz> wrote:

> > So, instead of doing #2911 as originally proposed, I propose to add a
> > configuration knob to disable the fallback:
> >   Xfrin/zones[n]/disable_axfr_fallback
> > This is set to false by default, and if set to true fallback from IXFR
> > to AXFR will be suppressed for that zone.
> 
> Thinking about that, we already have allow_ixfr option. Maybe we should move to
> some enum string, with options:

To be precise: you should mean use_ixfr.  I agree it's better to unify
the policy into a single configuration knob.  I'd name these:

>  • always-axfr
>  • always-ixfr
>  • ixfr-first

something like

- axfr-only (name it "only" to clarify it never tries IXFR) 
- ixfr-only (likewise.  but in this case it'd still use axfr when
  there's no "current" version of the zone)
- ixfr-first (default.  try IXFR as long as there's a "current"
  version, and fall back to AXFR if it fails)

My concern of this approach is that it'll be backward incompatible
change.  If we can still allow incompatible changes, the easiest way
is to simply migrate to the new semantics (probably renaming the
option).  But I guess we now need to think about compatibility more
seriously, after the public release version.  In that case a
compromise would be to keep the option name, define the type as "any"
so we can accept both boolean and strings, and support both old and
new versions.

---
JINMEI, Tatuya
Internet Systems Consortium, Inc.