User's Manual

VPN
Configuring the Site-to-Site VPN
Cisco ISA500 Series Integrated Security Appliance Administrator Guide 250
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For the example as illustrated in Figure 10, Site A has a LAN IP address of
10.10.10.0 and Site B has a LAN IP address of 10.20.20.0. When you
configure the Site-to-Site VPN on Site A, the local network is 10.10.10.0 and
the remote network is 10.20.20.0.
If the IP address object is not in the list, choose Create an IP Address to add
a new address object. To maintain the address objects, go to the
Networking -> Address Object Management page. See Address
Management, page 152.
NOTE The security appliance can support multiple subnets for IPSec VPN
tunnel, you may need to select a group address object including
multiple VLANs for local and remote network.
STEP 4 In the Advanced Settings tab, enter the following information:
• PFS Enable: Click On to enable Perfect Forward Secrecy (PFS) to improve
security, or click Off to disable it. If you enable PFS, a Diffie-Hellman
exchange is performed for every phase-2 negotiation. PFS is desired on the
keying channel of the VPN connection.
• DPD Enable: Click On to enable Dead Peer Detection (DPD), or click Off to
disable it. DPD is a method of detecting a dead Internet Key Exchange (IKE)
peer. The method uses IPsec traffic patterns to minimize the number of
messages required to confirm the availability of a peer. DPD is used to
reclaim the lost resources in case a peer is found dead and it is also used to
perform IKE peer failover.
If you enable DPD, enter the following information:
- Delay Time: Enter the value of delay time in seconds between DPD
sending two keepalive messages for this IPSec VPN connection. The
default is 30 seconds.
- Detection Timeout: Enter the value of detection timeout in seconds. If no
response and no traffic over the timeout, declare the peer dead. The
default is 120 seconds.
- DPD Action: Choose one of the following actions over the timeout:
Hold: Traffic from local network to remote network can trigger the
security appliance to re-initiate the IPSec VPN tunnel over the timeout.
We recommend that you use Hold when the remote peer uses a static IP
address.