For an end-to-site VPN, i.e. where a device (VPN client) is responsible for encapsulating the GRE packet, is it possible to send some custom data along with the GRE packet beyond just the standard payload.
Take for example a GRE packet assembled by a VPN client:
| IP header | GRE Header | Standard Payload |
Such that the Standard Payload looked like:
|Orignal IP Header| Orignal Payload|
In theory, if I wanted to append some extra data (Custom Data), such as some identifier of the VPN Client beyond an IP address to a GRE Packet payload, such that the packet then looked like:
|IP header| GRE Header | Custom Data + Standard Payload|
Would that be possible?
It seems if there was a way to access wherever the original packet is encapsulated into a GRE packet, you could make that payload whatever you desired, assuming the VPN server knew to strip off the Custom Data section of the payload.
Essentially, is there a way to add some custom data per packet to the payload or some place in the header for a given request. If so, at what level or where would this need to take place?