ZyWALL 5 User’s Guide
Chapter 13 Introduction to IPSec
217
NAT is incompatible with the
AH
protocol in both
Transport
and
Tunnel
mode. An IPSec
VPN using the
AH
protocol digitally signs the outbound packet, both data payload and
headers, with a hash value appended to the packet. When using
AH
protocol, packet contents
(the data payload) are not encrypted.
A NAT device in between the IPSec endpoints will rewrite either the source or destination
address with one of its own choosing. The VPN device at the receiving end will verify the
integrity of the incoming packet by computing its own hash value, and complain that the hash
value appended to the received packet doesn't match. The VPN device at the receiving end
doesn't know about the NAT in the middle, so it assumes that the data has been maliciously
altered.
IPSec using
ESP
in
Tunnel
mode encapsulates the entire original packet (including headers)
in a new IP packet. The new IP packet's source address is the outbound address of the sending
VPN gateway, and its destination address is the inbound address of the VPN device at the
receiving end. When using
ESP
protocol with authentication, the packet contents (in this case,
the entire original packet) are encrypted. The encrypted contents, but not the new headers, are
signed with a hash value appended to the packet.
Tunnel
mode
ESP
with authentication is compatible with NAT because integrity checks are
performed over the combination of the "original header plus original payload," which is
unchanged by a NAT device.
Transport
mode
ESP
with authentication is not compatible with
NAT, although NAT traversal provides a way to use
Transport
mode
ESP
when there is a
NAT router between the IPSec endpoints (See
for details).
Table 61
VPN and NAT
SECURITY PROTOCOL
MODE
NAT
AH
Transport
N
AH
Tunnel
N
ESP
Transport
N
ESP
Tunnel
Y
Содержание ZyXEL ZyWALL 5
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Страница 86: ...ZyWALL 5 User s Guide 84 Chapter 3 Wizard Setup ...
Страница 96: ...ZyWALL 5 User s Guide 94 Chapter 4 LAN Screens ...
Страница 102: ...ZyWALL 5 User s Guide 100 Chapter 5 Bridge Screens ...
Страница 130: ...ZyWALL 5 User s Guide 128 Chapter 7 WAN Screens Figure 45 WAN PPPoE Encapsulation ...
Страница 138: ...ZyWALL 5 User s Guide 136 Chapter 7 WAN Screens Figure 50 Dial Backup Setup ...
Страница 144: ...ZyWALL 5 User s Guide 142 Chapter 7 WAN Screens ...
Страница 152: ...ZyWALL 5 User s Guide 150 Chapter 8 DMZ Screens ...
Страница 174: ...ZyWALL 5 User s Guide 172 Chapter 10 Firewall Screens Figure 68 Creating Editing A Firewall Rule ...
Страница 179: ...ZyWALL 5 User s Guide Chapter 10 Firewall Screens 177 Figure 73 My Service Rule Configuration ...
Страница 220: ...ZyWALL 5 User s Guide 218 Chapter 13 Introduction to IPSec ...
Страница 238: ...ZyWALL 5 User s Guide 236 Chapter 14 VPN Screens Figure 110 VPN Rules IKE Network Policy Edit ...
Страница 261: ...ZyWALL 5 User s Guide Chapter 15 Certificates 259 Figure 122 My Certificate Details ...
Страница 280: ...ZyWALL 5 User s Guide 278 Chapter 16 Authentication Server Figure 133 Local User Database ...
Страница 317: ...ZyWALL 5 User s Guide Chapter 19 Bandwidth Management 315 ...
Страница 318: ...ZyWALL 5 User s Guide 316 Chapter 19 Bandwidth Management ...
Страница 352: ...ZyWALL 5 User s Guide 350 Chapter 21 Remote Management ...
Страница 366: ...ZyWALL 5 User s Guide 364 Chapter 23 Logs Screens Figure 188 Log Settings ...
Страница 389: ...ZyWALL 5 User s Guide Chapter 24 Maintenance 387 Figure 210 Restart Screen ...
Страница 390: ...ZyWALL 5 User s Guide 388 Chapter 24 Maintenance ...
Страница 416: ...ZyWALL 5 User s Guide 414 Chapter 27 WAN and Dial Backup Setup ...
Страница 432: ...ZyWALL 5 User s Guide 430 Chapter 30 DMZ Setup ...
Страница 492: ...ZyWALL 5 User s Guide 490 Chapter 37 System Information Diagnosis ...
Страница 508: ...ZyWALL 5 User s Guide 506 Chapter 38 Firmware and Configuration File Maintenance ...
Страница 520: ...ZyWALL 5 User s Guide 518 Chapter 40 Remote Management ...
Страница 536: ...ZyWALL 5 User s Guide 534 Chapter 42 Troubleshooting Figure 343 Java Sun ...
Страница 564: ...ZyWALL 5 User s Guide 562 Appendix C IP Subnetting ...
Страница 570: ...ZyWALL 5 User s Guide 568 Appendix E PPTP ...
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Страница 590: ...ZyWALL 5 User s Guide 588 Appendix G Triangle Route ...
Страница 620: ...ZyWALL 5 User s Guide 618 Appendix J Importing Certificates ...
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Страница 638: ...ZyWALL 5 User s Guide 636 Appendix O Brute Force Password Guessing Protection ...
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