ZyXEL Communications ZyWALL Troubleshooting Manual page 18

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No traffic flow through site-to-site IPSec VPN tunnel
Tunnel established but can't get traffic across:
 Make sure there are no IP conflicts between the two sites.
 Disable the ZyWALL routers firewall.
To disable the ZyWALL's firewall/policy control, go to:
Configuration  Firewall
Policy  Policy Control
 Verify that the host you are attempting to reach is pointing to the
ZyWALL for the default gateway.
 Check for conflicting policy/static routes. A misconfigured or
out of order route can cause problems. To verify the
policy/static route rules go to, Configuration  Network 
Routing.
 Verify that the host you are attempting to reach is listening for the
traffic you are sending to it. Example: If you're sending a ping
request to a device, make sure it is set to respond to ping/icmp
requests.
Windows:
netstat -an for a list of listening ports.
Open command prompt or powershell and type
OR Configuration  Security
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