Id Type And Content - ZyXEL Communications SBG5500-A User Manual

Figure 142 NAT Router Between IPsec Routers
Normally you cannot set up an IKE SA with a NAT router between the two IPsec routers because the NAT
router changes the header of the IPsec packet. NAT traversal solves the problem by adding a UDP port
500 header to the IPsec packet. The NAT router forwards the IPsec packet with the UDP port 500 header
unchanged. In the above figure, when IPsec router A tries to establish an IKE SA, IPsec router B checks
the UDP port 500 header, and IPsec routers A and B build the IKE SA.
For NAT traversal to work, you must:
• Use ESP security protocol (in either transport or tunnel mode).
• Use IKE keying mode.
• Enable NAT traversal on both IPsec endpoints.
• Set the NAT router to forward UDP port 500 to IPsec router A.
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 80 VPN and NAT
SECURITY PROTOCOL
AH
AH
ESP
ESP
Y* - This is supported in the SBG if you enable NAT traversal.

10.9.7 ID Type and Content

With aggressive negotiation mode (see
ID type and content since this identifying information is not encrypted. This enables the SBG 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 SBG does not allow you to save multiple active
rules with overlapping local and remote IP addresses.
With main mode (see
identity protection. In this case the SBG can only distinguish between different incoming SAs that
connect from remote IPsec routers that have dynamic WAN IP addresses. The SBG can distinguish
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
Chapter 10 VPN
MODE NAT
Transport N
Tunnel N
Transport Y*
Tunnel Y
Section 10.9.4 on page
Section 10.9.4 on page 189), the ID type and content are encrypted to provide
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189), the SBG identifies incoming SAs by