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Chapter 21 IPSec
VSG1435-B101 Series User’s Guide
266
Finally, NAT is compatible with ESP in tunnel mode because integrity checks are
performed over the combination of the "original header plus original payload,"
which is unchanged by a NAT device. The compatibility of AH and ESP with NAT in
tunnel and transport modes is summarized in the following table.
Y* - This is supported in the ZyXEL Device if you enable NAT traversal.
21.4.7 ID Type and Content
With aggressive negotiation mode (see Section 21.4.4 on page 264), the ZyXEL
Device identifies incoming SAs by ID type and content since this identifying
information is not encrypted. This enables the ZyXEL Device to distinguish
between multiple rules for SAs that connect from remote IPSec routers that have
dynamic WAN IP addresses.
Regardless of the ID type and content configuration, the ZyXEL Device does not
allow you to save multiple active rules with overlapping local and remote IP
addresses.
With main mode (see Section 21.4.4 on page 264), the ID type and content are
encrypted to provide identity protection. In this case the ZyXEL Device can only
distinguish between up to 12 different incoming SAs that connect from remote
IPSec routers that have dynamic WAN IP addresses. The ZyXEL Device can
distinguish up to 48 incoming SAs because you can select between three
encryption algorithms (DES, 3DES and AES), two authentication algorithms (MD5
and SHA1) and eight key groups when you configure a VPN rule (see Section 21.3
on page 252). The ID type and content act as an extra level of identification for
incoming SAs.
The type of ID can be a domain name, an IP address or an e-mail address. The
content is the IP address, domain name, or e-mail address.
Table 90 VPN and NAT
SECURITY
PROTOCOL
MODE NAT
AH Transport N
AH Tunnel N
ESP Transport Y*
ESP Tunnel Y
Table 91 Local ID Type and Content Fields
LOCAL ID
TYPE=
CONTENT=
IP Type the IP address of your computer.
DNS Type a domain name (up to 31 characters) by which to identify this
ZyXEL Device.