ZyXEL nbg-5715 Guia Do Utilizador
Chapter 18 IPSec VPN
NBG5715 User’s Guide
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NAT is not normally compatible with ESP in transport mode either, but the NBG5715’s NAT
Traversal feature provides a way to handle this. NAT traversal allows you to set up an IKE SA when
there are NAT routers between the two IPSec routers.
Traversal feature provides a way to handle this. NAT traversal allows you to set up an IKE SA when
there are NAT routers between the two IPSec routers.
Figure 85
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.
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.
• 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.
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 NBG5715 if you enable NAT traversal.
18.7.7 ID Type and Content
With aggressive negotiation mode (see
), the NBG5715 identifies
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.
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.
multiple active rules with overlapping local and remote IP addresses.
With main mode (see
), the ID type and content are encrypted to
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
different incoming SAs that connect from remote IPSec routers that have dynamic WAN IP
Table 58
VPN and NAT
SECURITY PROTOCOL
MODE
NAT
AH
Transport
N
AH
Tunnel
N
ESP
Transport
Y*
ESP
Tunnel
Y
A
B