IPsec Tunnel Interfaces Using Static VTI (CCIE Notes)

To minimize the complexity of configuration we can use IPsec profiles and associate them to Virtual Tunnel Interfaces. Its more like a Route Based VPN in Juniper NetScreen. There are other reasons why you would want to consider using VTIs to implement GRE over IPsec and they can be found here.

Jeremy Stretch has written a fantastic post on configuring GRE over IPsec using VTIs in the most simplest way possible – http://packetlife.net/blog/2008/jul/14/ipsec-quick-and-dirty/ so i won’t be bothering to include that all over again.

Just adding some notes below for my reference;

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IPsec over GRE – Configuration and Explanation (CCIE Notes)

As GRE does not have its own mechanism to encrypt traffic it depends on IPsec for getting the encryption job done. As opposed to GRE over IPsec, which encrypts anything that is encapsulated by GRE, IPsec over GRE encrypts only the payload and not the routing protocols running over a GRE tunnel.

In IPsec over GRE, the GRE tunnel is established over the internet, neighborship is formed and routes are exchanged and all of this is in clear text. We are only concerned with encrypting the interesting traffic flowing between the two peers. When securing the routing updates and routes isn’t a requirement and the major concern is to encrypt the information/payload flowing between the peers we use IPsec over GRE.

IPsec over GRE eliminates the additional overhead of encrypting the GRE header.

IPsec over GRE

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GRE over IPsec – Configuration and Explanation (CCIE Notes)

As GRE does not have its own mechanism to encrypt traffic it depends on IPsec for getting the encryption job done. The whole point of GRE over IPsec is to encrypt what is encapsulated by GRE.

In GRE over IPsec, the entire GRE encapsulated packet is encrypted with an IPsec header. The interesting traffic defined for IPsec encryption is the ‘GRE’ traffic between the source and destination, so the underlying payload is also encrypted along with the routing updates.

The goal is to establish EIGRP neighborship between two Cisco IOS routers R1 and R2 using the tunnel interface, exchange routes (loopback IPs) and make sure the communication takes place between the loopback networks. But allowing communication isn’t our only motive, we want to encrypt all traffic flowing between R1 and R2. That includes the routing information (EIGRP updates) sent over the internet and also the communication between the loopback networks.

Gre over IPsec

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