Actually you are both somewhat right: the consumer WLAN routers get their IP address via DHCP from the internet service provider. In the DHCP protocol there are so-called "option fields" to transmit certain kinds of information - the IP address itself being the main and most important one. Other option fields tell the client the default route and - among other things - also the DNS server (in DHCPv4 this is option field 6, see RFC1395, BOOTP Vendor Information Extensions). It is possible for the client to ignore some or all of these, but per default the information is used to configure the IP stack of the client in several respects, including but not limited to the DNS server.

DHCP is explicitly not intended to configure routers, but it is done nonetheless by ISPs. When their (usually riddled with a "user-friendly", aka "crippled" firmware) routers get configured that way they pass on this information to their (WLAN-) clients. I don't know about the situation in other continents but this is how it is done all over in Europe.

It is usually a good idea to NOT use the DNS of the ISP at all and hand-pick a DNS server of your own choice for several reasons:

First, this is a good place to find out more about you and which hosts you contact. The ISP can get that information analysing your IP packets too, true, but this way you dont even need to contact a server to make them aware that you are interested in it.

Second, the DNS servers at least with Germanies ISPs are greatly hacked. IP addresses they don't want you to see are resolved not to their IP addresses but to "127.0.0.1". Some of these hacks have legal background (the German authorities think this is "internet security" and order that to prevent traffic to these sites), some hacks simply express the ISPs opinion that "we don't want our customers to go there". For many years i.e. a certain porn site was known to be "masked" this way by Vodaphone. Now, i don't care that much about porn sites but i like to decide myself if a site is worthy of my attention or not. (corollary: if someone you despise gets treated unfairly you should object as well - chances are the next one treated the same way may be you) Especially when the ones deciding upon masking or not an IP address is are a secret body (in earnest - in Germany this is decided secretly and expressly foregoing due process. But don't worry! Its all in the name of freedom and democracy.) instead of a public court.

I use 3 DNS servers. The first two are operated by UncensoredDNS, a Danish ISP who operates also this public DNS servers. The third one is cloudflare, but even though i appreciate their "no logs, no ads" policy it is there only as a backup:

Code:

91.239.100.100
89.233.43.71
1.1.1.1

I hope this helps.

bakunin