What's the difference between DNS on the LAN or WAN?

[Easy Limits]

I have a AC56U running the latest Merlin firmware. I was noticing that I can enter DNS numbers on the WAN tab and the LAN tab, under DHCP server. Is there any benefit to one over the other?

 

[ColinTaylor]

They perform different roles.

The settings on the WAN page are used by the router itself to do DNS lookups. The settings on LAN/DHCP are explicit server addresses that are given out to DHCP clients.

So normally the WAN DNS points to an external DNS server, and the LAN/DHCP entry is left empty which is equivalent to typing in the router's own address (192.168.1.1). What this means is that a DHCP client will receive the router's IP address as it's DNS server. So name lookups from the client will go to the DNS server running on the router (dnsmasq). If the router can't resolve the name it will forward it on to the server specified on the WAN page.

The advantage of doing it this way is that the router can cache frequently used names locally rather than the client having to go out to the internet every time. This means that name resolution is much faster. It has the added benefit that you can use DNS to resolve the names of devices on your LAN.

 

[Smokie]

Funny that I was looking at the exact same thing last night and wondering the same.

 

[Ronald Schwerer]

I assume that the LAN's DNS server (0.0.0.0) just caches the names in RAM and gets initialized on reboot. Any other way to clear that cache (incase the actual IP changes)?

 

[ColinTaylor]

I assume that the LAN's DNS server (0.0.0.0) just caches the names in RAM and gets initialized on reboot.

Correct. Although the router's DNS server address won't ever be 0.0.0.0 .

Any other way to clear that cache (incase the actual IP changes)?

You could restart the dnsmasq service or send it a SIGHUP. But it shouldn't normally be necessary because the upstream authoritative DNS server should be altering the TTL.