[systemd-devel] systemd-resolve and name servers order

[Mark Rogers]

On Wed, 11 Oct 2023 at 09:37, Marc <Marc at f1-outsourcing.eu> wrote:

> Having 3 different nameservers reporting different results?
>

An example I have seen quite frequently is where there is an internal DNS
which resolves local (internal) server resources and forwards anything else
to an external server such as 8.8.8.8. When the internal DNS fails
(typically because it's been taken down for server updates) it would be
useful for clients to still have access to the external DNS - even if they
can't access local resources they can still access external ones, and in
reality they probably already had the internal resource IPs cached anyway.
So having client DNS configured as 192.168.x.x (primary) and 8.8.8.8
(secondary) makes sense.

But as you say this isn't how resolv.conf was designed (nor other DNS
clients in my experience), and configuring a client that way will cause a
lot of internal requests to fail even when the local DNS is operational.
It's a shame that DNS clients can't have server configurations much like MX
records where a random choice is made between servers of the same priority,
but lower priority options can be configured too (as that would also allow
load balancing of requests across multiple servers as now). I don't know of
any clients that do this, though.

Obviously there are other solutions to the problem described above (eg
having multiple internal servers, although my experience was in the SOHO
environment where that would be excessive). If as Rafał says Windows
prioritises the first DNS option then I'm pretty sure that wasn't always
the case, but it's been well over a decade since I got out of Windows IT
support! But there are certainly use cases for allowing DNS server
prioritisation in this way.
-- 
Mark Rogers // More Solutions Ltd (Peterborough Office) // 0344 251 1450
Registered in England (0456 0902) 21 Drakes Mews, Milton Keynes, MK8 0ER
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