You'd think that an unresponsive nameserver would be flagged dead, and such information be cached. Does anyone know whether that's actually done in Bind 8.3.4? Or perhaps not by default?
This certainly does not happen when all authoritative nameservers are unresponsive. See http://www.nanog.org/mtg-0310/wessels.html, in particular pages 23 and 24 of the slides. In my simulations with 100% packet loss, DNS caches running BIND8, dnscache, W2000, and W2003 all amplified the user's query rates. Only BIND9 attenuated. The results do depend on the actual query rate, however. At a higher query rate, the other caches would/should attenuate as well (perhaps reaching their hard-coded rate limits), but I don't have the exact numbers. It would be interesting to repeat the simulation and take out, say, half of a set of authoritative nameservers during the middle of the test. Duane W.