Interesting Marco. Based on your reply I checked and just realized that the sensors are using iptables. I thought they used to use just tcpwrappers? Did that change with version 6 or has it been like that a long time and I just never noticed?
In any event, iptables (marco's explanation) is a much more plausible explanation if you can ping other subnets but they can't ping you.
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...