Nat Traversal Configuration; Id Type And Content; Figure 88 Nat Router Between Ipsec Routers - ZyXEL Communications Vantage CNM User Manual

Vantage CNM User's Guide

Figure 88 NAT Router Between IPSec Routers

Normally you cannot set up a VPN connection with a NAT router between the two IPSec
routers because the NAT router changes the header of the IPSec packet. In the previous figure,
IPSec router A sends an IPSec packet in an attempt to initiate a VPN. The NAT router changes
the IPSec packet's header so it does not match the header for which IPSec router B is
checking. Therefore, IPSec router B does not respond and the VPN connection cannot be built.
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. IPSec router
B checks the UDP port 500 header and responds. IPSec routers A and B build a VPN
connection.

11.8.1 NAT Traversal Configuration

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.
In order for IPSec router A (see
from IPSec router B, set the NAT router to forward UDP port 500 to IPSec router A.

11.9 ID Type and Content

With aggressive negotiation mode, 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. Telecommuters can use separate passwords to simultaneously
connect to the ZyXEL device from IPSec routers with dynamic IP addresses.
Note: 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.
175
Figure 88 on page 175) to receive an initiating IPSec packet
Chapter 11 Configuration > VPN