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Temporarily changing DNS servers and search domains in Tiger
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Temporarily changing DNS servers and search domains in Tiger

I'm working on a VPN configuration utility which needs to temporarily change the DNS servers and search domains while the VPN connection is active (VPN traffic goes over a separate interface). In Panther, I did this by editing resolv.conf. In Tiger, very few programs seem to consult resolv.conf.

When I try to modify the SCDynamicStore (kSCDynamicStoreDomainState, kSCCompNetwork, kSCCompGlobal, kSCEntNetDNS), and call SCDynamicStoreNotifyValue for good measure the changes stick, but nothing happens. If I don't run as root, I get kSCStatusAccessError when I try to write to it, and if I retrieve the entry later, it does come back as I stored it, but the output of scutil --dns (and the resolver behavior) does not change.

Ideally I could associate the nameserver and search domain overrides with the interface, so when the interface goes down, the values associated with the previous interface are restored. However, the default route is not going to go through the VPN interface in most cases (in fact, the nameserver is on the public Internet), so I don't think it will be considered "primary". The VPN interface does show up as State:/Network/Interface/<iface>/IPv4 for example, but not in the output of SCNetworkInterfaceCopyAll().

If necessary, I can leave a daemon running to maintain state. (I tried that too, keeping the connection to the SCDynamicStore open, but it didn't help.) It is OK if my changes are relatively brittle - for example, I can use notifications to see if the user does something like change locations/sets and reinstall my changes or not, as appropriate if the VPN connection can be reestablished.

What is the right way to do this?



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