
208 Chapter 13 VPN
NN47923-500
IPSec using ESP in Tunnel mode encapsulates the entire original packet
(including headers) in a new IP packet. The new IP packet's source address is the
outbound address of the sending Business Secure Router, and its destination
address is the inbound address of the VPN device at the receiving end. When
using ESP protocol with authentication, the packet contents (in this case, the
entire original packet) are encrypted. The encrypted contents, but not the new
headers, are signed with a hash value appended to the packet.
Tunnel mode ESP with authentication is compatible with NAT because integrity
checks are performed over the combination of the original header plus original
payload, which is unchanged by a NAT device. Transport mode ESP with
authentication is not compatible with NAT, although NAT traversal provides a
way to use Transport mode ESP when there is a NAT router between the IPSec
endpoints (see “NAT Traversal” on page 213 for details).
Secure Gateway Address
Secure Gateway Address is the WAN IP address or domain name of the remote
secure gateway. You can specify this for a VPN rule in the VPN Branch Office
Rule Setup screen (see Figure 71 on page 222).
If the remote secure gateway has a static WAN IP address, enter it in the Secure
Gateway Address field. You can alternatively enter the domain name of the
remote secure gateway (if it has one) in the Secure Gateway Address field.
Table 46 VPN and NAT
Security Protocol Mode NAT
AH Transport N
AH Tunnel N
ESP Transport N
ESP Tunnel Y
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