Perhaps I am not understanding something in your question. I have been doing IPSec VPN to protect GRE tunnels on 1721 routers since very early 12.3 mainline code. Or perhaps you are referring to tunnel protection used with the Virtual Tunnel Interface which I find supported on 1721 since 12.3(14)T.
If I am not understanding what you are asking then please clarify.
OK, I guess the "tunnel protection ipsec profile profile_name" command is available but it looks like "tunnel mode ipsec" isn't. Maybe you don't need that last command to get the ipsec tunnel to work? I always just resorted to building my crypto maps statically on 1721's because of that.
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...