In your case Full-duplex = configured duplex and Half-duplex=negotiated duplex. When auto-negotiation fails or is disabled, speed can be 'sensed' by the device but the devices fall back to half duplex as duplex is something that either has to be same on both ends or has to be negotiated.
It is apparent that your ISP has not properly configured his end. Double check that. Have a look at this:
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...