Strange Mac OS X name resolution

Now on one Mac I have a strange issue I never had before: Sporadically, e.g. after a fresh boot, name resolution does not work. While nearly every kind of application is effected, Safari, Mail, etc. even ping. To my surprise, though, dig(1) does reliable work in this kind of stuck system state. After some review it turned out that Mac OS X provides different DNS resolution services of the classic Unix / Posix services - that apparently can get out-of-sync from what the classic resolution configuration would use. To flush them:

10.4: lookupd -flushcache
10.5: dscacheutil -flushchache
10.6: sudo killall -HUP mDNSResponder

For me, under Snow Leopard (Mac OS 10.6), killing the mDNSResponder did actually indeed help! I’ll have to keep an eye on the situation, if it’s getting too annoying I’ll have to try a clean re-install. Sigh!

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