forwarders used in order or based on RTT ?

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forwarders used in order or based on RTT ?

Bob Harold
The BIND ARM (9.16.2) says:
"There may be one or more forwarders, and they are queried in turn until the list is exhausted
or an answer is found."

But
says:
"Forwarders are selected based on an RTT(round-trip-time)-based algorithm"

So which is correct?  
And did it change at some point?

--
Bob Harold
DNS and DHCP Hostmaster - UMNet
Information and Technology Services (ITS)
[hidden email]   734-512-7038

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Re: forwarders used in order or based on RTT ?

Matus UHLAR - fantomas
On 16.10.20 09:56, Bob Harold wrote:

>The BIND ARM (9.16.2) says:
>"There may be one or more forwarders, and they are queried in turn until
>the list is exhausted
>or an answer is found."
>
>But
>https://lists.isc.org/pipermail/bind-users/2015-August/095544.html
>says:
>"Forwarders are selected based on an RTT(round-trip-time)-based algorithm"
>
>So which is correct?

both are. The ARM does not say they are queried in defined order.
The order is defined by RTT

>And did it change at some point?

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Matus UHLAR - fantomas, [hidden email] ; http://www.fantomas.sk/
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Re: forwarders used in order or based on RTT ?

Bob Harold
That is certainly not obvious.  How do I request improving the manual?

"in turn" would seem to imply "in order", and the order would logically be the order I listed them.

--
Bob Harold
DNS and DHCP Hostmaster - UMNet
Information and Technology Services (ITS)
[hidden email]   734-512-7038


On Fri, Oct 16, 2020 at 10:21 AM Matus UHLAR - fantomas <[hidden email]> wrote:
On 16.10.20 09:56, Bob Harold wrote:
>The BIND ARM (9.16.2) says:
>"There may be one or more forwarders, and they are queried in turn until
>the list is exhausted
>or an answer is found."
>
>But
>https://lists.isc.org/pipermail/bind-users/2015-August/095544.html
>says:
>"Forwarders are selected based on an RTT(round-trip-time)-based algorithm"
>
>So which is correct?

both are. The ARM does not say they are queried in defined order.
The order is defined by RTT

>And did it change at some point?

--
Matus UHLAR - fantomas, [hidden email] ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
Fucking windows! Bring Bill Gates! (Southpark the movie)
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Re: forwarders used in order or based on RTT ?

Bind-Users forum mailing list
In reply to this post by Matus UHLAR - fantomas
On Fri, Oct 16, 2020 at 10:22 AM Matus UHLAR - fantomas
<[hidden email]> wrote:

>> On 16.10.20 09:56, Bob Harold wrote:
> >The BIND ARM (9.16.2) says:
> >"There may be one or more forwarders, and they are queried in turn until
> >the list is exhausted or an answer is found."
> >
> >But [an old mailinglist post] says:
> >"Forwarders are selected based on an RTT(round-trip-time)-based algorithm"
> >
> >So which is correct?
>
> both are. The ARM does not say they are queried in defined order.
> The order is defined by RTT

To be fair, the ARM strongly implies in its context that it's the
order you put them in the list.

The ARM discrepancy has already been noted by ISC, but the first bug
report in the long long ago on it was never really fixed.    They
raised the issue again internally a few months ago and so I would
anticipate that the ARM will be fixed in a not too distant release.

https://gitlab.isc.org/isc-projects/bind9/-/issues/2030
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Re: forwarders used in order or based on RTT ?

@lbutlr
In reply to this post by Bob Harold
On 16 Oct 2020, at 08:36, Bob Harold <[hidden email]> wrote:
> That is certainly not obvious.  How do I request improving the manual?
>
> "in turn" would seem to imply "in order", and the order would logically be the order I listed them.]

I disagree. In turn means one is tried, then if that fails the next is tried. There is no implication at all that the order they are tried in is the order specified.

It would not hurt anything to say they were tried in turn accords to RTT, but as it stands the documentation doesn’t say what you think it says.

Again, "in turn" doesn’t mean "in the order I expect" it simply means one after another until all are checked (or one succeeds).


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"Wuh, I think so, Brain, but I prefer Space Jelly."

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Re: forwarders used in order or based on RTT ?

Warren Kumari
On Sun, Oct 18, 2020 at 2:32 PM @lbutlr <[hidden email]> wrote:

>
> On 16 Oct 2020, at 08:36, Bob Harold <[hidden email]> wrote:
> > That is certainly not obvious.  How do I request improving the manual?
> >
> > "in turn" would seem to imply "in order", and the order would logically be the order I listed them.]
>
> I disagree. In turn means one is tried, then if that fails the next is tried. There is no implication at all that the order they are tried in is the order specified.
>
> It would not hurt anything to say they were tried in turn accords to RTT, but as it stands the documentation doesn’t say what you think it says.
>
> Again, "in turn" doesn’t mean "in the order I expect" it simply means one after another until all are checked (or one succeeds).


"In turn" might not strictly mean in the order listed (the definitions
converge around 1: "in succession", or 2: a causal step from a
previous outcome), but there is *implication* that it is in the order
listed.
If I said "The carolers visited the houses in turn", the *implication*
is that they visited the first house, then the second, then the third,
etc and not the first, then the seventeenth, etc.

Yes, there is ambiguity - it appears that this usage is that the
succession is "in RTT order", and not "in listed order", but the fact
that it is ambiguous, and people are unsure what is meant,
demonstrates a bug in the documentation.

W

>
>
> --
> "Are you pondering what I'm pondering?"
> "Wuh, I think so, Brain, but I prefer Space Jelly."
>
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Re: forwarders used in order or based on RTT ?

Vicky Risk
Administrator
In reply to this post by Bob Harold
The ARM was updated in 9.16.6.  Sorry it took us so long!

from https://gitlab.isc.org/isc-projects/bind9/-/issues/2030
Forwarders are typically used when an administrator does not wish for
all the servers at a given site to interact directly with the rest of
the Internet. For example, a common scenario is when multiple internal
DNS servers are behind an Internet firewall. Servers behind the firewall
forward their requests to the server with external access, which queries
Internet DNS servers on the internal servers' behalf.

Another scenario (largely now superseded by Response Policy Zones) is to
send queries first to a custom server for RBL processing before
forwarding them to the wider Internet.

There may be one or more forwarders in a given setup. The order in which
the forwarders are listed in ``named.conf`` does not determine the
sequence in which they are queried; rather, ``named`` uses the response
times from previous queries to select the server that is likely to
respond the most quickly. A server that has not yet been queried is
given an initial small random response time to ensure that it is tried
at least once. Dynamic adjustment of the recorded response times ensures
that all forwarders are queried, even those with slower response times.
This permits changes in behavior based on server responsiveness.

Vicky
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Re: forwarders used in order or based on RTT ?

Warren Kumari
On Mon, Oct 19, 2020 at 11:26 AM Victoria Risk <[hidden email]> wrote:

>
> The ARM was updated in 9.16.6.  Sorry it took us so long!
>
> from https://gitlab.isc.org/isc-projects/bind9/-/issues/2030
> Forwarders are typically used when an administrator does not wish for
> all the servers at a given site to interact directly with the rest of
> the Internet. For example, a common scenario is when multiple internal
> DNS servers are behind an Internet firewall. Servers behind the firewall
> forward their requests to the server with external access, which queries
> Internet DNS servers on the internal servers' behalf.
>
> Another scenario (largely now superseded by Response Policy Zones) is to
> send queries first to a custom server for RBL processing before
> forwarding them to the wider Internet.
>
> There may be one or more forwarders in a given setup. The order in which
> the forwarders are listed in ``named.conf`` does not determine the
> sequence in which they are queried; rather, ``named`` uses the response
> times from previous queries to select the server that is likely to
> respond the most quickly. A server that has not yet been queried is
> given an initial small random response time to ensure that it is tried
> at least once. Dynamic adjustment of the recorded response times ensures
> that all forwarders are queried, even those with slower response times.
> This permits changes in behavior based on server responsiveness.


Awesome, thank you -- that's clean and easy to understand.
W

>
> Vicky
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>
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--
I don't think the execution is relevant when it was obviously a bad
idea in the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair
of pants.
   ---maf
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