Showing results for 
Search instead for 
Did you mean: 

tunneling concept problem



in tunneling concept in general we have concepts of 

carrier , passenger , transport protocol

in case we are using 

GRE over IPSec


here GRE should be passenger and IPsec carrier

but in which case IPSec becomes as a Transport ?

in case of underlay protocol(infrastructure protocol) is IPSec so it can be transport

but mostly we have IP Protocol as a Transport 

my query is how possible IPSec is used as a Transport?

in other reference i see :

Generally, a logical interface that provides a way to encapsulate passesnger packets inside a transport protocol

but where we use term of carrier protocol




4 Replies 4

Hall of Fame
Hall of Fame

here is the detailed good explanation in the cisco document for reference :



***** Rate All Helpful Responses *****

How to Ask The Cisco Community for Help

Hello and thanks for your reply , Yes i see that link and one time i read it.
My Question is in my example GRE over IPSec
if IPSec is transport
GRE is carrier or passenger
and what will that traffic which is encapsulated by GRE !

but generaly tunnel related discussion X over Y means X is passenger and Y is Carrier


From my perspective and my understanding Transport means that protocol which is used to build network infrastructure, i know IP Security is Layer 3 protocol for encryption and also authentication of IP Packet being used !!!

but can purely uses IPsec for building Network infrastructure ....

if NO and from my side i also say NO

if IPSec is transport

GRE should be carrier in this case

because before configuring we can not figure it out what will be our traffic ?

and maybe i am confused with definition of Transport protocol in tunneling

maybe i should be revised 


one other idea is we take IPSec as a protocol which encrypting GRE packet and GRE also encapsulated our Data(pasenger protocol in it)

it is Transport for GRE not that things i mentioned before !


but still am i right IPsec ia not in format of network infrastructure protocol and is a protocol for carrying GRE ....



did my previous analysis was correct?

IPSec is transport the Carrier protocol (we can take this one idea)

but still we have like Layer 3 protocols is used for infrastructure (Routing ability)

mostly transport means (as i've understood) ability to gives a routing ;

IPsec although is a Layer 3 (in some reference is mentioned something else)

but how can is being used as a Transport individually

or maybe my description about Transport not correct !

transport for carrier

transport routing infrastructure

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: