
Chapter 6 • The IP Security Protocol (IPsec) 111
Intranet
Intranet
CD
B
A
X
Y
M
Internet
Figure 6–4: IP security tunneling.
are encrypted. The ESP Header is designed to provide several different
services (some overlapping with the Authentication Header), including
the following.
• Confidentiality of datagrams through encryption.
• Authentication of data origin through the use of public key
encryption
• Antireplay services through the same sequence number mecha-
nism as provided by the Authentication Header
• Limited traffic flow confidentiality through the use of security
gateways
The ESP Header can be used in conjunction with an Authentication
Header. In fact, unless ...