We have routers that run gre tunnels and pixs that then ipsec encrypt before the packet gets to our remote sites. I would like to know if, you can run transport mode for vpn site to site connectivity as transport mode just encrypts the payload rather then the whole packet and only adds a few bytes.
Secondly, Is there anything to watch out for as far as applications are concerned in transport mode.
Thirdly, is there any advantage for voip packets when running in transport mode, thinking that the whole packet does not get encrypted, hence faster delivery i.e smaller packets. We will be having qos in place as well.