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| Chapter 18 VPN Screens |
| Table 103 VPN Setup | |
| LABEL | DESCRIPTION |
| Remote | This is the IP address(es) of computer(s) on the remote network behind the remote |
| Address | IPSec router. |
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| This field displays N/A when the Secure Gateway Address field displays 0.0.0.0. In |
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| this case only the remote IPSec router can initiate the VPN. |
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| The same (static) IP address is displayed twice when the Remote Address Type |
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| field in the |
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| The beginning and ending (static) IP addresses, in a range of computers are |
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| displayed when the Remote Address Type field in the |
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| Key) screen is configured to Range. |
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| A (static) IP address and a subnet mask are displayed when the Remote Address |
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| Type field in the |
| Encap. | This field displays Tunnel or Transport mode (Tunnel is the default selection). |
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| IPSec Algorithm | This field displays the security protocols used for an SA. |
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| Both AH and ESP increase ZyXEL Device processing requirements and |
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| communications latency (delay). |
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| Secure | This is the static WAN IP address or URL of the remote IPSec router. This field |
| Gateway IP | displays 0.0.0.0 when you configure the Secure Gateway Address field in the VPN- |
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| IKE screen to 0.0.0.0. |
| Modify | Click the Edit icon to go to the screen where you can edit the VPN configuration. |
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| Click the Remove icon to remove an existing VPN configuration. |
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| Apply | Click this to save your changes and apply them to the ZyXEL Device. |
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| Cancel | Click this return your settings to their last saved values. |
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18.6 Keep Alive
When you initiate an IPSec tunnel with keep alive enabled, the ZyXEL Device automatically renegotiates the tunnel when the IPSec SA lifetime period expires (see Section 18.12 on page 288 for more on the IPSec SA lifetime). In effect, the IPSec tunnel becomes an “always on” connection after you initiate it. Both IPSec routers must have a ZyXEL
If the ZyXEL Device has its maximum number of simultaneous IPSec tunnels connected to it and they all have keep alive enabled, then no other tunnels can take a turn connecting to the ZyXEL Device because the ZyXEL Device never drops the tunnels that are already connected.
When there is outbound traffic with no inbound traffic, the ZyXEL Device automatically drops the tunnel after two minutes.
18.7 VPN, NAT, and NAT Traversal
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, but a NAT device between the IPSec endpoints rewrites the source or destination address. As a result, the VPN device at the receiving end finds a mismatch between the hash value and the data and assumes that the data has been maliciously altered.
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