Hello,
On 6 Jan 2021, at 16:19, Tapani Tarvainen ipfire@tapanitarvainen.fi wrote:
On Wed, Jan 06, 2021 at 03:14:52PM +0000, Michael Tremer (michael.tremer@ipfire.org) wrote:
On 6 Jan 2021, at 12:02, Paul Simmons mbatranch@gmail.com wrote:
On 1/6/21 4:17 AM, Jonatan Schlag wrote:
When unbound has no information about a DNS-server a timeout of 376 msec is assumed. This works well in a lot of situations, but they mention in their documentation that this could be way too low. They recommend a timeout of 1126 msec for satellite connections (https://nlnetlabs.nl/documentation/unbound/unbound.conf).
A small nit, they actually suggest 1128 ... and that's indeed what the patch has:
- unknown-server-time-limit: 1128
But that's trivial. The point:
I am not entirely sure what this is supposed to fix.
It is possible that a DNS response takes longer than 376ms, indeed. Does it harm us if we send another packet? No.
If you are behind a slow satellite link, it can take more than that *every time*. So you would always have sent another query before getting a response to the previous one.
True, but aren’t these extra-ordinary circumstances?
On a regular network we want to keep eyeballs happy and when packets get lost or get sent to a slow server, we want to try again - sooner rather than later.
If we would set this to a worst case setting (let’s say 10 seconds), then even for average users DNS resolution will become slower.
With TCP that would mean never getting a response, because you'd always terminate the connection too soon. With UDP, I'm not sure, depends on how unbound handles incoming responses to queries it's already deemed lost and sent again. Adjusting delay-close might help. But it may be it would not work at all when the limit is too small.
That would mean that someone installing IPFire in some remote location with a slow link would conclude that it just doesn't work.
The downside of increasing the limit is that sometimes replies will take longer when a packet is lost on the way because we'd wait longer before re-sending. So it should not be increased too much either.
I don't have data to judge what the limit should be, but I'd tend to trust nllabs recommendation here and go with the suggested 1128 ms.
Did anyone actually experience some problems here that this needs changing?
@Jonatan: What is your motivation for this patch?
-- Tapani Tarvainen