Comment 34 for bug 923685

I think we agree on the main principle, which is: append, unless we are confident that dynamic nameserver information will be supplied. In the case of ifupdown the condition means: there is a logical interface definition that is either "dhcp" or contains "dns-nameservers".

#26 differs from #33 only in applying the additional condition that there must be evidence that the logical interface definition is automatically activated, i.e., for logical interface L there is a line "auto L" and the default mapping is in effect. (Any use of "source" or "mapping" calls into question whether the default mapping is in effect.)

I follow your reasoning in #33, though; and not applying the additional condition will simplify the code considerably.