DNS definition: router, PC, or both

[GRoston]

I can think of two ways to configure DNS servers:
1: Router defined

• On router: Define the desired DNS servers
• On Windows 7, Ethernet adapter properties: Set the DNS server to the address of the router

2: Computer defined

• On router: Define the desired DNS servers (not sure that this matters in this case)
• On Windows 7, Ethernet adapter properties: Set the addresses of the desired DNS servers

Questions:

1. Are these two approach equivalent? The former is preferred because it allows one to manage DNS servers for a network in one place.
2. In the second case, what role, if any, do the defined DNS servers in the router play?

I am asking this because, after some recent changes, one application is not properly resolving host addresses... Thanks!

 

[samuria]

DNS on the router is only used by default via DHCP if it's set on the PC that's the one used. If the router is used it's an extra hop as the PC asks the router who knows nothing so it goes to a DNS server which replies to the router who passed it back to PC so there is delay. If it's a cheap router it can suffer performance if it's doing lots of extra work doing DNS. A DNS server will hold Billions of records

 

[Alejandro85]

They're not equivalent, but are similar. As you said, the main advantage of setting DNSs in the router is to have a central place for many computers, so if you ever need a change, you do it in a single place and it applies to every single computer out there.


The second one also as an advantage that individual computers can override the network-wide setting and use its own, if ever the need arises. In that case, the router settings are ignored (the router isn't even queried), so it doesn't play any role here, for that computer at least.
What really happens is that, when the computer needs to resolve a DNS, it goes to, say, your ISP directly, skipping the router. In the first case Windows will query the router (without any further knowledge of what happens after that) and the router in turn will delegate the query to your ISP or prefered DNS server.


Also, as Samuria said, there is a performance hit when using the router as an intermediate DNS server, as there is an extra query going on. It's unlikely to be noticeable, as it's only an extra LAN call, strictly speaking, it's a bit slower.

If it's a cheap router it can suffer performance if it's doing lots of extra work doing DNS. A DNS server will hold Billions of records

It won't affect that much actually. Your router internal DNS server won't hold those "billions" of records, instead will only forward calls to some other server, and, at most, will keep some as a cache for performance, that in time will be phased out. Even with really cheap routers, it's unlikely to be a problem, unless serving a VERY big network of active computers.

 

[samuria]

net gear routers often fall over if there are a few users using it as dns

 

[GRoston]

As noted, I asked this question because of some wrong DNS behavior I experienced after changing my system configuration to that which I referred to as 'router defined'. Once I did this, one particular application could not access a specific domain via its domain name, but it could when I used its IP address.

Based on another discussion, and as suggested also by samuria, the problem I experienced (with my TP-LINK router) might be that the router has a broken DNS forwarder. When I switched to the 'computer defined' configuration, then everything again works (with my choice of DNS server as opposed to my ISP's).

Thanks for your helpful replies.