Chapter 21 IPSec

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.

Table 90 VPN and NAT

SECURITY

MODE

NAT

PROTOCOL

 

 

AH

Transport

N

 

 

 

AH

Tunnel

N

 

 

 

ESP

Transport

Y*

 

 

 

ESP

Tunnel

Y

 

 

 

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 260), 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 260), 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 248). 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 91 Local ID Type and Content Fields

LOCAL ID

CONTENT=

TYPE=

 

IP

Type the IP address of your computer.

 

 

DNS

Type a domain name (up to 31 characters) by which to identify this

 

ZyXEL Device.

 

 

262

 

VSG1432-B101 Series User’s Guide