Verify that the concentrator has a route pointing to the network where the DNS server resides. Without it, the public filter does not allow DNS traffic and the DNS packet wil be dropped. If all is in order but still not working, try this. Create a new filter, identical to the public (default) filter and apply it to the public interface. This worked for me and hopefully, it'll work for you too. You should also have a look at CSCdt78452.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...