pfSense

+1 and so far i used a modified system.php file adding more of those and they get properly saved in the config and also used by the system

this is true add ipv6 and it has even more need

Maybe someone could instead fix/nuke the misleading note from the GUI, instead of putting in more DNS servers that will never get used for anything? (Cf. https://github.com/freebsd/freebsd/blob/master/include/resolv.h#L128)

That's for the host resolver itself -- dnsmasq and unbound in forwarding mode will pick up more.

Yup. It'd be awesome if those settings were moved to the relevant place (i.e., DNS forwarder/resolver settings). This thing is just causing perpetual user confusion. Some description improvements here: https://github.com/pfsense/pfsense/pull/3338

PR https://github.com/pfsense/pfsense/pull/3373
It seems to work too easily, what have I forgotten?

Note: I kept this in the General Setup page where it has been since eternity. Just made it so a variable number of DNS Servers can be entered. (Kill Bill mentioned moving the UI for this elsewhere)

getting this error whe trying to add more dns servers

A gateway can not be assigned to DNS '8.8.8.8' server which is on a directly connected network.
A gateway can not be assigned to DNS '8.8.4.4' server which is on a directly connected network.

2.3.3-DEVELOPMENT (amd64) 
built on Fri Jan 13 14:45:19 CST 2017 
FreeBSD 10.3-RELEASE-p15

that error happens re-saving current setup with 4 dns servers

ok already had manually added staic route for 8.8.8.8 and 8.8.4.4 causes failure in error checking

So that sort of config should have failed the input validation already prior to his change. The code considers anything on a "really locally connected" network or pointed to by a static route in the config to be "local" and a DNS server on such a network/address should not have a gateway specified.

I guess it would be possible to do more validation checks, and if the existing static route for that address already points out the selected gateway, then it is OK. But actually it is easy for the user to either remove the static route or not select a gateway for the DNS server (and then it will use the static route they already set up).