A gateway can not be assigned to DNS server which is on a directly connected network

geminux · Feb 18, 2021, 2:21 PM

Hello,

I'm facing an issue while configuring a DNS forwarder.
In my configuration, the upstream DNS server is also the upstream gateway.

Let's say that :

LAN is 192.168.0.0/24
WAN is 192.168.255.0/24. (private network is not a mistake, this is an interconnection to the upstream router). .253 is pfsense, .254 is the upstream router.
An upstream gateway is declared on WAN interface with 192.168.255.254
The upstream router also privide the DNS service (And I have to use it for this WAN interface.
It is related to MPTCP bypass function on the upstream router. No choice)
(of course nat is disabled on pfsense)

So in "general config" I try to add 192.168.255.254 as DNS forwarder, and make it use the gateway (which has the same IP)

It gives the following error :

A gateway can not be assigned to DNS '192.168.255.254' server which is on a directly connected network.

I can't figure out if it's a feature or a bug. What would be the point of such limitation ?

Please note that everything is working well if I use an online DNS like 1.1.1.1 or 8.8.8.8 except that I will have some MPTCP limitation if I can't use 192.168.255.254 instead.
I'm using version 2.4.5-RELEASE-p1.

Does anybody have an explanation (or a solution) ?

Thanks

geminux · Feb 18, 2021, 3:35 PM

OK I'm dumb...

It's obvious that this gateway will be used to reach 192.168.255.254 DNS since it is a direct attached subnet... There is no risk that it uses any other gateway...

I sticked too hard to the rule "at least one DNS must be set per gateway in a multiwan environment" In the case of a DNS in a WAN subnet, selecting none is fine because routing through this interface is implicit.

My use case is not the most widespread but maybe a clarification could be made in the documentation. Meanwhile answer can now be found here