LesD wrote:
I sort of half understand what you mean. You are saying that somehow the 'router' resolving DNS addresses is different from 'clients'.
Yes.
LesD wrote:
I don't understand the difference.
The router is an internet accessing device and needs to contact a DNS server to resolve addresses. What clients on the network then do with regards to their DNS needs is a completely separate issue.
LesD wrote:
I am talking about DNS lookup from client machines as you indicated, except all my PCs have fixed IPs rather than using DHCP.
Then the DNS servers set under DHCP Server Configuration in LAN 1 won't affect your machines. If, however, you had PCs with dynamic IPs, they would receive the DNS information from whatever you set in that window.
LesD wrote:
To give a concrete example:
The router has address 10.27.27.250
The PCs are set with fixed IP and set to use the router (10.27.27.250) as the DNS server.
I then set in LAN1 the two OpenDNS addresses for the DNS servers.
If I do not tick the 'force' button then my PCs do not use the specified OpenDNS servers.
I am certain of that because I have firewall rules which block all DNS lookups that are not going via the OpenDNS servers.
That makes perfect sense. If you don't tick the 'force' button, the DrayTek will use its normal configuration i.e. using the DNS servers suggested by the ISP. The PCs will go to the DrayTek for a DNS resolution, and the DrayTek will give them one ('forwarding' whatever information it got from the ISP).
The PCs have static IPs so won't receive the information specified in the LAN 1 settings page, since that only applies to DHCP clients.
LesD wrote:
If I do not tick the 'force' option then no one can do DNS lookups.
That also makes sense, because the DrayTek will try and access the ISP DNS servers, and will find that its access is blocked by the firewall settings.
LesD wrote:
If I remove the firewall rules then DNS works but then the OpenDNS content filtering is lost as the OpenDNS servers are not being used.
Again, that makes sense because the PCs are using the DrayTek's DNS server, and the DrayTek is using the ISP's DNS server.
LesD wrote:
The only way I can force the user PCs to use the OpenDNS servers is by ticking the 'Force ... LAN1' option.
As you currently have it setup, yes. You could also give the PCs dynamic IPs, set the OpenDNS servers in the LAN 1 DNS server setup page, and then you wouldn't have to tick the 'force' checkbox.
LesD wrote:
Which ten brings me back to my question: Once I have specified the DNS servers in LAN1 why do I need the 'force..' ticked?
Because those DNS server settings are for LAN 1 DHCP clients, not the router.
