Chapter 10 VPN
SBG5500 Series User’s Guide
188
Figure 140
Transport and Tunnel Mode IPsec Encapsulation
Transport Mode
Transport
mode is used to protect upper layer protocols and only affects the data in the IP packet. In
Transport
mode, the IP packet contains the security protocol (
AH
or
ESP
) located after the original IP
header and options, but before any upper layer protocols contained in the packet (such as TCP and
UDP).
With
ESP,
protection is applied only to the upper layer protocols contained in the packet. The IP header
information and options are not used in the authentication process. Therefore, the originating IP address
cannot be verified for integrity against the data.
With the use of
AH
as the security protocol, protection is extended forward into the IP header to verify
the integrity of the entire packet by use of portions of the original IP header in the hashing process.
Tunnel Mode
Tunnel
mode encapsulates the entire IP packet to transmit it securely. A
Tunnel
mode is required for
gateway services to provide access to internal systems.
Tunnel
mode is fundamentally an IP tunnel with
authentication and encryption. This is the most common mode of operation.
Tunnel
mode is required for
gateway to gateway and host to gateway communications.
Tunnel
mode communications have two
sets of IP headers:
•
Outside header
: The outside IP header contains the destination IP address of the VPN gateway.
•
Inside header
: The inside IP header contains the destination IP address of the final system behind the
VPN gateway. The security protocol appears after the outer IP header and before the inside IP
header.
10.9.3 IKE Phases
There are two phases to every IKE (Internet Key Exchange) negotiation – phase 1 (Authentication) and
phase 2 (Key Exchange). A phase 1 exchange establishes an IKE SA and the second one uses that SA to
negotiate SAs for IPsec.
Summary of Contents for SBG5500-A
Page 12: ...12 PART I User s Guide...
Page 44: ...44 PART II Technical Reference...
