ZyXEL P-660HNU-F1 User Guide - Page 213

IPSec and NAT, IPSec Algorithms, Key Management

Page 213 highlights

Figure 110 IPSec Architecture Chapter 16 VPN IPSec Algorithms The ESP (Encapsulating Security Payload) Protocol (RFC 2406) and AH (Authentication Header) protocol (RFC 2402) describe the packet formats and the default standards for packet structure (including implementation algorithms). The Encryption Algorithm describes the use of encryption techniques such as DES (Data Encryption Standard) and Triple DES algorithms. The Authentication Algorithms, HMAC-MD5 (RFC 2403) and HMAC-SHA-1 (RFC 2404, provide an authentication mechanism for the AH and ESP protocols. Key Management Key management allows you to determine whether to use IKE (ISAKMP) or manual key configuration in order to set up a VPN. 16.6.2 IPSec and NAT Read this section if you are running IPSec on a host computer behind the ZyXEL Device. NAT is incompatible with the AH protocol in both Transport and Tunnel mode. An IPSec VPN using the AH protocol digitally signs the outbound packet, both data payload and headers, with a hash value appended to the packet. When using AH protocol, packet contents (the data payload) are not encrypted. A NAT device in between the IPSec endpoints will rewrite either the source or destination address with one of its own choosing. The VPN device at the receiving end will verify the integrity of the incoming packet by computing its own hash value, and complain that the hash value appended to the received packet doesn't match. The VPN device at the receiving end doesn't know about the NAT in the middle, so it assumes that the data has been maliciously altered. ADSL Series User's Guide 213

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Chapter 16 VPN
ADSL Series User’s Guide
213
Figure 110
IPSec Architecture
IPSec Algorithms
The
ESP
(Encapsulating Security Payload) Protocol (RFC 2406) and
AH
(Authentication Header)
protocol (RFC 2402) describe the packet formats and the default standards for packet structure
(including implementation algorithms).
The Encryption Algorithm describes the use of encryption techniques such as DES (Data Encryption
Standard) and Triple DES algorithms.
The Authentication Algorithms, HMAC-MD5 (RFC 2403) and HMAC-SHA-1 (RFC 2404, provide an
authentication mechanism for the
AH
and
ESP
protocols.
Key Management
Key management allows you to determine whether to use IKE (ISAKMP) or manual key
configuration in order to set up a VPN.
16.6.2
IPSec and NAT
Read this section if you are running IPSec on a host computer behind the ZyXEL Device.
NAT is incompatible with the
AH
protocol in both
Transport
and
Tunnel
mode. An IPSec VPN using
the
AH
protocol digitally signs the outbound packet, both data payload and headers, with a hash
value appended to the packet. When using
AH
protocol, packet contents (the data payload) are not
encrypted.
A NAT device in between the IPSec endpoints will rewrite either the source or destination address
with one of its own choosing. The VPN device at the receiving end will verify the integrity of the
incoming packet by computing its own hash value, and complain that the hash value appended to
the received packet doesn't match. The VPN device at the receiving end doesn't know about the
NAT in the middle, so it assumes that the data has been maliciously altered.