D-Link EXPRESS ETHERNETWORK VDI-604 User Manual page 35

public WAN IP addresses is a common method used by hackers to test
whether your WAN IP address is valid.
Discard PING from WAN side: By enabling this option, the VDI-604 will
not reply to ping (ICMP) request packets from the Internet.
VPN Pass-Through
The Broadband Router supports VPN (Virtual Private Network)
pass-through for both PPTP (Point-to-Point Tunneling Protocol) and
IPSec (IP Security). Once VPN pass-through is enabled, there is no need
to open up virtual services. Multiple VPN connections can be made
through the Broadband Router. This is useful when you have many VPN
clients on the LAN network.
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