GRE over IPSEC

[cdrobey]

Can anyone point me to the Cisco documentation that explains when GRE over IPSEC is required? And when IPSEC can be used without GRE?

Thanks.

[shawn]

Below is an excerpt from http://www.cisco.com/en/US/netsol/ns341/ns396/ns172/ns155/networking_solutions_white_paper09186a00800a8445.shtml

GRE

Generic Routing Encapsulation (GRE) tunnels provide a designated pathway across the shared Wide Area Network (WAN) and encapsulate traffic with new packet headers, which ensures delivery to specific destinations. The network is private because traffic can enter a tunnel only at an endpoint. Tunnels do not provide true confidentiality (as does encryption), but can carry encrypted traffic. IPsec can be used to encrypt data before it enters and after it leaves the GRE tunnel.

***

You may want to look at the GRE RFC 1701 (http://www.ietf.org/rfc/rfc1701.txt).

Regards,

Shawn

[mhussein]

Here is a document:

Configuring a GRE Tunnel over IPSec with OSPF

http://www.cisco.com/en/US/tech/tk583/tk372/technologies_configuration_example09186a00800a43f6.shtml

If you want to setup LAN-to-LAN tunnel using static routing, then you don't need GRE. But if you need routing protocols to run across the tunnel (actual protocol traffic to establish routing neighbours) then GRE is required to carry the protocol traffic.

Regards,

Mustafa