Transparent tunneling allows secure transmission between the VPN Client and a secure gateway through a router serving as a firewall. The router might also be configured for Network Address Translation (NAT) or Port Address Translations (PAT).
Transparent tunneling encapsulates Protocol 50 (ESP) traffic within UDP packets. It allows for both IKE (UDP 500) and Protocol 50 to be encapsulated in TCP packets before they are sent through the NAT or PAT devices and/or firewalls. The most common application for transparent tunneling is behind a home router performing PAT.
Not all devices support multiple simultaneous connections behind them. Some cannot map additional sessions to unique source ports. Check with your device's vendor to see if this limitation exists. Some vendors support Protocol 50 (ESP) PAT, which might let you operate without enabling transparent tunneling.
To use transparent tunneling, the IPSec group in the Cisco VPN device must be configured to support it.
Transparent Tunneling is enabled by default. To disable this parameter, clear the check box. We recommend that you keep this parameter enabled.
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