Fortinet FortiGate 4000 - Manual (Page 242)

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AutoIKE IPSec VPNs IPSec VPN
4 Optionally, configure NAT Traversal.
5 Optionally, configure Dead Peer Detection.
Use these settings to monitor the status of the connection between VPN peers. DPD
allows dead connections to be cleaned up and new VPN tunnels established. DPD is
not supported by all vendors.
6 Select OK to save the phase 1 parameters.
XAuth: Enable as a Server
Encryption
method Select the encryption method used between the XAuth client, the FortiGate
unit and the authentication server.
PAP— Password Authentication Protocol.
CHAP—Challenge-Handshake Authentication Protocol.
MIXED—Select MIXED to use PAP between the XAuth client and the
FortiGate unit, and CHAP between the FortiGate unit and the
authentication server.
Use CHAP whenever possible. Use PAP if the authentication server does
not support CHAP. (Use PAP with all implementations of LDAP and some
implementations of Microsoft RADIUS). Use MIXED if the authentication
server supports CHAP but the XAuth client does not. (Use MIXED with the
Fortinet Remote VPN Client.).
Usergroup Select a group of users to be authenticated by XAuth. The individual users
within the group can be authenticated locally or by one or more LDAP or
RADIUS servers.
The user group must be added to the FortiGate configuration before it can
be selected here.
Enable Select Enable if you expect the IPSec VPN traffic to go through a gateway
that performs NAT. If no NAT device is detected, enabling NAT traversal
has no effect. Both ends of the VPN (both VPN peers) must have the same
NAT traversal setting.
Keepalive
Frequency If you enable NAT-traversal, you can change the number of seconds in the
Keepalive Frequency field. This number specifies, in seconds, how
frequently empty UDP packets are sent through the NAT device to ensure
that the NAT mapping does not change until P1 and P2 keylife expires. The
keepalive frequency can be from 0 to 900 seconds.
Enable Select Enable to enable DPD between the local and remote peers.
Short Idle Set the time, in seconds, that a link must remain unused before the local
VPN peer considers it to be idle. After this period of time expires, whenever
the local peer sends traffic to the remote VPN peer it also sends a DPD
probe to determine the status of the link. To control the length of time that
the FortiGate unit takes to detect a dead peer with DPD probes, configure
the Retry Count and the Retry Interval.
Retry Count Set the number of times that the local VPN peer retries the DPD probe
before it considers the channel to be dead and tears down the security
association (SA). To avoid false negatives because of congestion or other
transient failures, set the retry count to a sufficiently high value for your
network.
Retry Interval Set the time, in seconds, that the local VPN peer unit waits between
retrying DPD probes.
Long Idle Set the time, in seconds, that a link must remain unused before the local
VPN peer pro-actively probes its state. After this period of time expires, the
local peer sends a DPD probe to determine the status of the link even if
there is no traffic between the local peer and the remote peer.