Id Type And Content - ZyXEL Communications NBG5715 User Manual

Chapter 18 IPSec VPN
Figure 86 NAT Router Between IPSec Routers
A
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 59 VPN and NAT
SECURITY PROTOCOL
AH
AH
ESP
ESP
Y* - This is supported in the NBG5715 if you enable NAT traversal.

18.7.7 ID Type and Content

With aggressive negotiation mode (see
incoming SAs by ID type and content since this identifying information is not encrypted. This
enables the NBG5715 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 NBG5715 does not allow you to save
multiple active rules with overlapping local and remote IP addresses.
With main mode (see
provide identity protection. In this case the NBG5715 can only distinguish between up to 12
different incoming SAs that connect from remote IPSec routers that have dynamic WAN IP
addresses. The NBG5715 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
and content act as an extra level of identification for incoming SAs.
140
MODE NAT
Transport N
Tunnel N
Transport Y*
Tunnel Y
Section 18.7.4 on page
Section 18.7.4 on page
138), the NBG5715 identifies
138), the ID type and content are encrypted to
Section 18.4 on page
B
123). The ID type
NBG5715 User's Guide