FYI: Manually provided DNS addresses are higher priority than DHCP's
As an FYI to folks here concerned about the issue, manually entered DNS addresses do indeed supercede any provided by DHCP despite what you might be led to believe by the appearance of the
Network->Advanced->DNS preference pane.
When you manually enter a DNS server address in Mac OS X Leopard's Network preference pane, the manually entered address(es) appear below any DHCP-provided addresses (which are shown in grey as they are unchangeable), leading one to assume that DHCP-provided addresses always have priority over any a user may specify.
However, a check of the /etc/resolv.conf file generated by Mac OS X shows that in fact user-provided DNS addresses will supercede any provided by DHCP.
As an example, if your router promotes itself as a DHCP server, its IP address, say "192.168.0.253," will appear, greyed out, in the Network->Advanced->DNS preferences pane.
If you then add, say, OpenDNS' addresses of "208.67.222.222" and "208.67.220.220," the preferences window will show:
But the generated /etc/resolv.conf will show the order Mac OS X will actually reference the servers is:
While this is non-intuitive with respect to how the addresses are displayed in the preference pane, it is exactly the way one would hope things would work - allowing you to specify DNS servers to be used in lieu of any a router provides, especially handy if the router propagates the address of a DNS server that is having issues or is simply overloaded or offline.
Note that as I do not have an unpatched copy of Leopard available, I cannot say if this has always been Mac OS X's behavior or if this ordering was added by Security Update 2008-005.
Regardless, this also means no special modifications are required to try to "turn off" the honoring of DHCP-provided DNS server addresses.
When you manually enter a DNS server address in Mac OS X Leopard's Network preference pane, the manually entered address(es) appear below any DHCP-provided addresses (which are shown in grey as they are unchangeable), leading one to assume that DHCP-provided addresses always have priority over any a user may specify.
However, a check of the /etc/resolv.conf file generated by Mac OS X shows that in fact user-provided DNS addresses will supercede any provided by DHCP.
As an example, if your router promotes itself as a DHCP server, its IP address, say "192.168.0.253," will appear, greyed out, in the Network->Advanced->DNS preferences pane.
If you then add, say, OpenDNS' addresses of "208.67.222.222" and "208.67.220.220," the preferences window will show:
192.168.0.253 (greyed out)
208.67.222.222
208.67.220.220But the generated /etc/resolv.conf will show the order Mac OS X will actually reference the servers is:
nameserver 208.67.222.222
nameserver 208.67.220.220
nameserver 192.168.0.253While this is non-intuitive with respect to how the addresses are displayed in the preference pane, it is exactly the way one would hope things would work - allowing you to specify DNS servers to be used in lieu of any a router provides, especially handy if the router propagates the address of a DNS server that is having issues or is simply overloaded or offline.
Note that as I do not have an unpatched copy of Leopard available, I cannot say if this has always been Mac OS X's behavior or if this ordering was added by Security Update 2008-005.
Regardless, this also means no special modifications are required to try to "turn off" the honoring of DHCP-provided DNS server addresses.
Quad 2.5 GHz G5, 5 GB | 2.33 GHz MBP C2D 2 GB, Mac OS X (10.5.4)
