All traffic will be encapsulated first with GRE tunnel's source and destination. You will not see difference between transport mode vs tunnel mode. Transport mode actually is recommended mode for DMVPN, because it saves 20 bytes overhead.
The only case you have to use tunnel mode is when using dual tier DMVPN, MGRE and encryption are on different routers.
Are you saying that if I was just running a Point-to-Point VPN with IPsec enabled, transport mode would show the inner IP addresses of the virtual tunnel interface while tunnel mode would hide the virtual tunnel ip addresses.
BUT, since I am running DMVPN over mGRE inside IPsec, the mode (tunnel or transport) is really mute because mGRE has already protected the virtual tunnel interface IP addresses?
That is correct. Transport mode will only encrypt the data payload and use the original IP header; tunnel mode will encrypt the whole IP packet (header + payload) and use a new IP header.
When using DMVPN, all traffic pass through the tunnel interface will be encapsulate first with GRE source and destination, and same ip address will be used for ipsec peers. Therefor, there is no difference of using transport vs tunnel mode.
Transport mode would be preferred as it would not hide the ip headers and even if it did it will replace the same at the other end of the tunnel, as you are stating that peer ip's will be the same as well. Also using the tunnel mode in this case will be like encrypting the ip header and then replacing it with the same ip header at the other end of the tunnel.
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...