If you want to use Smart DNS from Synology and have the machine be reachable via Tailscale, starting it with:
tailscale up --accept-dns=false
would likely work. The Tailscale DNS features like Magic DNS won't work, but connectivity would.

I don't think we have a way to make both Smart DNS and Magic DNS work simultaneously, at least not yet.

And now I realize I wrote SmartDNS when I really wanted to say MagicDNS 😁

I (want to) use Tailscale's MagicDNS, no SmartDNS is involved at all, sorry for the confusion.

To use MagicDNS, I assume that the Synology's /etc/resolv.conf needs to be updated to add the ...tailscale.net domain and 100.100.100.100 resolver, right? I guess that this is what causing the error message, because of insufficient permissions?

Could you paste the output of ls -l /etc/resolv.conf on the Synology device?
If it is a symbolic link, please also ls -l the link target.

It's a plain file (no symlink), here are the permissions:

# ls -l /etc/resolv.conf
-rw-r--r-- 1 root root 182 Dec 21 10:11 /etc/resolv.conf

Thanks!

I don't expect this to ever work on DSM7 where we don't run as root. AFAIK there's no API for us to change it as our non-root user.

If you use the SOCKS5 proxy for outgoing connections it'll do its own name resolution.

I assume you enabled TUN mode? Ah, yes, I see you did.

You could manually change the Synology DNS server to 100.100.100.100 but then Tailscale wouldn't know where to forward on non-Tailscale queries to unless you specified a global DNS server in your Tailnet config. Perhaps we need a node-local way to specify that.

1.22 added a tailscale configure-host command which can be run at each boot. I don't know if it addresses /etc/resolv.conf.

Mentioned in #4017 (comment)

The Synology CLI Administrators Guide mentions:

synonet {--set_dns} dns

But the description is:

Manually assign DNS server when all the network adapters are set to Manual IP.

Thanks @jimmybrancaccio for pointing out this ticket. To folks who have weighed in so far, I've tried on DSM7.2.2 the following suggestions with the results as noted (all as root):

1. tailscale configure-host

• No impact on /etc/resolv.conf or ability to successfully resolve TS node names

2. tailscale configure synology

• Same results as (1)

3. synonet --set_dns 100.100.100.100

• /etc/resolv.conf content is replaced with "nameserver 100.100.100.100" (previous nameserver 192.168.1.1 no longer present). TS node names resolve normally, as do all global DNS attempts, as well as local DNS managed at my 192.168.1.1)

4. Manually updating /etc/resolv.conf to

nameserver  100.100.100.100
nameserver  192.168.1.1

• Same results as (3).

I am not clear on how nslookup was able to resolve global DNS and local DNS entries (which is not something this NAS is managing) when only 100.100.100.100 was present. My TS DNS configuration is to override local DNS with:

1. 100.100.100.100 (Magic DNS)
2. 192.168.0.1 (Split DNS for one local domain only)
3. 1.1.1.1

Is 100.100.100.100 somehow able to access my account-specific configuration? I figured that for this to work, all rules would have to be written into /etc/resolv.conf , but that doesn't seem to be the case. If not, is the solution here to simply force our DSM7 boxes to use 100.100.100.100 when running Tailscale (either through synonet --set_dns or in the Synology control panel)?

Just to cut to the chase for anyone else that is looking for a quick solution, this is what is working for me now so you may give it a try:

1. Configure your https://login.tailscale.com/admin/dns settings as needed for your local network, including the option to override local DNS.

2. Modify the task you run at NAS boot to look like this (only the first line is new as you would have already had the second line per https://tailscale.com/kb/1131/synology):

synonet --set_dns 100.100.100.100
tailscale configure-host; synosystemctl restart pkgctl-Tailscale.service

@pjdubya thanks for the solution. I was close, what I missed was synonet --set_dns adding this to /etc/resolv.conf manually did not work for me. Also have to add search tailb11111.ts.net to /etc/resolv.conf in order for local net resolution to work.
So all seems good at present. Thanks

@pjdubya Thanks, your solution worked great for me! I've been struggling with this issue for a few months 😩

Do you know if the synonet --set_dns 100.100.100.100 essentially do the same thing as setting the Manually configure DNS server to 100.100.100.100?

and if that's doing the same thing, why do we need to run that task at NAS boot? Is there something that changes that configuration upon reboot? 🤔