Billion Electric Company BiGuard 30 - Manual (Page 163)

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Transport Mode
- This mode is used to provide data security between two networks. It provides
protection for the entire IP packet and is sent by adding an outer IP header
corresponding to the two tunnel end-points. Since tunnel mode hides the original IP
header, it provides security of the networks with private IP address space.
E.2.3 Tunnel Mode AH
AH is typically applied to a data packet in the following manner:
IP AH/E TC IP Dat
AH/E TC IP Dat
Original Packet
IP Header TCP Data
Org IP Header TCP Data
Packet with IPSec Authentication Header
AH
Authenticated
New IP Header