When do i have to use a gre over ipsec tunnel? i have heard that when i m using a routing protocol and vpn site to site i need a

[josedilone19]

i have configured a network with ospf and a vpn site to site without gre tunnel and it works very well. I want to know, when do i have to use gre tunnel over ipsec

[rvarelac · Accepted solution]

Hi josedilone19

GRE is used when you need to pass Broadcast or multicast traffic.  That's the main function of GRE.

Generic Routing Encapsulation (GRE) is a protocol that encapsulates packets in order to route other protocols over IP networks

However there are some other important aspect to consider: 

In contrast to IP-to-IP tunneling, GRE tunneling can transport multicast and IPv6 traffic between networks
GRE tunnels encase multiple protocols over a single-protocol backbone.
GRE tunnels provide workarounds for networks with limited hops.
GRE tunnels connect discontinuous sub-networks.
GRE tunnels allow VPNs across wide area networks (WANs).

-Hope this helps -