GRE over IPsec (Cisco VPN)

GRE over IPsec (Cisco VPN)

This section describes how to configure a FortiGate VPN that is compatible with Cisco-style VPNs that use GRE in an IPsec tunnel.

The following topics are included in this section:

  • Overview
  • Configuring the FortiGate unit
  • Configuring the Cisco router
  • Troubleshooting

 

Overview

Cisco products that include VPN support often use Generic Routing Encapsulation (GRE) protocol tunnel over IPsec encryption. This chapter describes how to configure a FortiGate unit to work with this type of Cisco VPN.

Cisco VPNs can use either transport mode or tunnel mode IPsec. Before FortiOS 4.0 MR2, the FortiGate unit was compatible only with tunnel mode IPsec.

 

Example FortiGate to Cisco GRE-over-IPsec VPN

cisco-gre-over-ipsec

In this example, users on LAN1 are provided access to LAN2.


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