January 9, 2009

Fix Slow DNS in Leopard

Filed under: Uncategorized — kenjun @ 9:05 am

With Leopard, a major change occurred in DNS lookups. Any program in Leopard that can use version 6 IP addresses will send out a new type of DNS lookup request – the SRV Record. In Tiger and previous OS X versions, DNS lookups were A record requests.

SRV records are new (sadly, 8 years old is new in the DNS world), provide more information than A records, but have terrible support in terms of hardware (your DSL router or cable modem) and DNS servers that answer with SRV information. For every SRV request that Leopard sends it must wait for a valid reply. If the request fails, Leopard must try again. If it fails again, Leopard will finally ask for an A record. This is one reason why Mac users are experiencing slow Internet on new Macs with Leopard or after upgrading to Leopard from Tiger.


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