Synology RT1900AC DNS management : Too much DNS settings

[kevincork]

I'm lot in my DNS settings with my router.

My internet is coming from a 4G modem
The network is managed my my Synology Router

Synology settings
Local Network : (inside the DHCP settings) Primary DNS and Secondary DNS (my Pihole and 1.1.1.1)
Internet > Manually configure DNS server Preferred DNS server and Alternative DNS Server
(my Pihole and 1.1.1.1)

Coming back to my 4G modem, which by the way in a different subnetwork
I have Primary DNS Server
Secondary DNS Server with 1. pihole and second 1.1.1.1

1.The main issue I have is, I can't setup a individual DNS for a specific device,
E.g I would like to use a DNS Geo unlocked for my AppleTV, but whatever DNS I add in the device settings is overwritten by my Synology DNS ( I think the one which is registered in Internet, Preference DNS Server)
if I leave this field bank then I have no internet...

2. for my 4G modem which is in a different sub, should I use external DNS only such 1.1.1.1 or can I still mention my PiHole local server ?

3. In my route local network settings, is this only for internal DNS (PiHole) or external DNS (1.1.1.1)

[jfb]

@kevincork

I have Primary DNS Server
Secondary DNS Server with 1. pihole and second 1.1.1.1

If you set up your DNS this way, some of the traffic won't go to the Pi-Hole, it will go directly to Cloudflare. The terms "primary" and "secondary" can be misleading; both DNS entries will be used.

Why should Pi-hole be my only DNS server?

Reduced Ad Blocking Capability The main reason you should Pi-hole as your only DNS server is that you will see increased performance in the blocking of ads. If you have two DNS servers (Pi-hole and something else), your network clients may not always query Pi-hole for name resolution. If a query happens to be answered from a non-Pi-hole DNS server, your block lists will not apply (since that DNS server doesn't know about them). All Queries Need To Go Through Pi-hole First Since other DNS se…

Can you make a sketch of your network setup and post it here?

[kevincork]

@jfb

Reduced Ad Blocking Capability The main reason you should Pi-hole as your only DNS server is that you will see increased performance in the blocking of ads. If you have two DNS servers (Pi-hole and something else), your network clients may not always query Pi-hole for name resolution. If a query happens to be answered from a non-Pi-hole DNS server, your block lists will not apply (since that DNS server doesn’t know about them). All Queries Need To Go Through Pi-hole First Since other DNS serv…

Thank you, I actually though that Primary DNS was always used and secondary always in case of the first one wasn't responding, kind of fail-over.

Here is the map, my setup is a bit complex

Modem:

DLINK DWR-921 (192.168.0.1)
Primary DNS Server PiHole (10.0.3.70)
Secondary DNS Server 1.1.1.1

Router :

Synology RT1900 AC
Internet settings :
IP Address 192.168.0.77
Subnet mask 255.255.255.0
Gateway 192.168.0.1
DNS Server PiHole (10.0.3.70)
Set as default gateway Enabled
Manually configure DNS Server
Preferred DNS server PiHole (10.0.3.70)
Alternative DNS Server 1.1.1.1

Local Network DHCP
10.0.3.2 - 10.0.4.129
Gateway 10.0.3.1
Primary DNS PiHole (10.0.3.70)
Secondary DNS 1.1.1.1
Forward known DNS server : Enabled.

PiHole connected on internet (raspberry pi)

WiFi

Netgear Orbi 3Gbs in bridge mode
PiHole setup on Docker, connected to ethernet from the NAS to the WiFi AP but not in used yet.

[musicsnob]

@kevincork

1.The main issue I have is, I can’t setup a individual DNS for a specific device,
E.g I would like to use a DNS Geo unlocked for my AppleTV, but whatever DNS I add in the device settings is overwritten by my Synology DNS ( I think the one which is registered in Internet, Preference DNS Server)

@kevincork Don't use DHCP for those devices. Instead, assign them static IPs and whichever DNS server you'd like.

Also, like @jfb said, don't use a secondary/alternate DNS server on your router. Otherwise, your ad blocking will only appear to work some of the time. Instead, tell Pi-hole to forward DNS requests to multiple DNS servers, such as 1.1.1.1 and 1.0.0.1. Pi-hole will filter out all of the ad server requests while sending the non-ad requests to Cloudflare's DNS for normal resolution.