Here are the custom rules I use:
Code:
;Switch system update server
sun.hac.lp1.d4c.nintendo.net,Deny
beach.hac.lp1.eshop.nintendo.net,Deny
;Switch phone home
receive-lp1.dg.srv.nintendo.net,Deny
receive-lp1.er.srv.nintendo.net,Deny
;Switch connection test
;conntest.nintendowifi.net,Redirect,xploit.ninty.ninja
The last line is if you want to redirect the connection test page the Switch tries to load when you connect to a network.
Here's a link to LocalDNS just in case. It's no frills but it's lightweight and dead simple:
https://gbatemp.net/threads/release-localdns-a-new-way-to-block-updates.445930/
Remember to check your routers settings first to see if it is capable of blocking the offending URLs. I wouldn't use a proxy, public DNS, or any other blocking method if my router could block traffic on anything but port 80. I have an HTPC that's always on anyways so using a DNS emulator is not a big inconvenience for me.