Chapter 11 IPSec VPN
P-793H User’s Guide
158
Aggressive mode does not provide as much security as main mode because the identity of the
ZyXEL Device and the identity of the remote IPSec router are not encrypted. It is usually used
when the address of the initiator is not known by the responder and both parties want to use
pre-shared keys for authentication (for example, telecommuters).
11.1.2.2 VPN, NAT and NAT Traversal
In the following example, there is another router (
A
) between router
X
and router
Y
.
Figure 80
VPN/NAT Example
If router
A
does NAT, it might change IP addresses (source or destination), port numbers
(source or destination), or any combination of these. If router
X
and router
Y
try to establish a
VPN tunnel, the authentication fails because authentication depends on the original IP
addresses and port numbers.
Most routers that support NAT (like router
A
) have an IPSec pass-through feature. This
feature helps router
A
recognize VPN packets and route them appropriately. If router
A
has
this feature, router
X
and router
Y
can establish a VPN tunnel as long as the active protocol is
ESP. (See
for more information about active protocols.)
If router A does not have an IPSec pass-through or if the active protocol is AH, you can solve
this problem by enabling NAT traversal. In NAT traversal, router
X
and router
Y
add an extra
header to the IKE SA and IPSec SA packets. If you configure router
A
to forward these
packets unchanged, router
X
and router
Y
can establish a VPN tunnel.
You have to do the following things to set up NAT traversal.
• Enable NAT traversal on the ZyXEL Device and remote IPSec router.
• Configure the NAT router to forward packets with the extra header unchanged. The extra
header may be UDP port 500 or UDP port 4500, depending on the standard(s) the ZyXEL
Device and remote IPSec router support.
"
You must enable NAT traversal on the ZyXEL Device and the remote IPSec
router, and you must configure the NAT router to forward packets with the
extra header unchanged.
11.1.3 IPSec SA Overview
Once the ZyXEL Device and remote IPSec router have established the IKE SA, they can use
the IKE SA to securely negotiate IPSec SAs through which to send data between computers on
the networks.
Summary of Contents for G.SHDSL.bis 4-port Security Gateway P-793H
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Page 7: ...Safety Warnings P 793H User s Guide 7 This product is recyclable Dispose of it properly ...
Page 8: ...Safety Warnings P 793H User s Guide 8 ...
Page 30: ...List of Figures P 793H User s Guide 30 ...
Page 36: ...List of Tables P 793H User s Guide 36 ...
Page 38: ...38 ...
Page 68: ...Chapter 4 Point to 2 point Configuration P 793H User s Guide 68 ...
Page 70: ...70 ...
Page 114: ...Chapter 7 Network Address Translation NAT Screens P 793H User s Guide 114 ...
Page 116: ...116 ...
Page 152: ...Chapter 10 Content Filtering P 793H User s Guide 152 ...
Page 180: ...Chapter 12 Static Route P 793H User s Guide 180 ...
Page 194: ...Chapter 14 Dynamic DNS Setup P 793H User s Guide 194 ...
Page 216: ...Chapter 16 Universal Plug and Play UPnP P 793H User s Guide 216 ...
Page 217: ...217 PART IV Maintenance System 219 Logs 225 Tools 229 Diagnostic 235 ...
Page 218: ...218 ...
Page 224: ...Chapter 17 System P 793H User s Guide 224 ...
Page 234: ...Chapter 19 Tools P 793H User s Guide 234 ...
Page 238: ...238 ...
Page 244: ...Chapter 21 Introducing the SMT P 793H User s Guide 244 ...
Page 248: ...Chapter 22 General Setup P 793H User s Guide 248 ...
Page 256: ...Chapter 23 WAN Setup P 793H User s Guide 256 ...
Page 262: ...Chapter 24 LAN Setup P 793H User s Guide 262 ...
Page 278: ...Chapter 27 Static Route Setup P 793H User s Guide 278 ...
Page 308: ...Chapter 30 Filter Configuration P 793H User s Guide 308 ...
Page 310: ...Chapter 31 SNMP Configuration P 793H User s Guide 310 ...
Page 312: ...Chapter 32 System Password P 793H User s Guide 312 ...
Page 322: ...Chapter 33 System Information Diagnosis P 793H User s Guide 322 ...
Page 352: ...Chapter 37 Schedule Setup P 793H User s Guide 352 ...
Page 360: ...360 ...
Page 366: ...Appendix B Wall mounting Instructions P 793H User s Guide 366 ...
Page 400: ...Appendix F IP Address Assignment Conflicts P 793H User s Guide 400 ...
Page 404: ...Appendix G Common Services P 793H User s Guide 404 ...
Page 432: ...Appendix K Legal Information P 793H User s Guide 432 ...
Page 443: ...Index P 793H User s Guide 443 ...
Page 444: ...Index P 793H User s Guide 444 ...