Netbios 137/138 through ASA- UDP request discard logs
The traffic is initiated from the host mentioned in the log message (10.145.0.66) and the broadcast is naturally destined for the broadcast address (10.145.0.255) of that subnet as you can see from the log message also. The source and destination are naturally on the same network as broadcast traffic wont go beyond the first L3 hop (router hop) in the network.
I dont know the operation of Netbios enough to give you a good explanation but to my understanding in Windows host networks if no separate name server is used the operation is based on broadcast traffic.
In your case the ASA naturally sees this traffic as its broadcast traffic and drops it as expected.
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...