Restrictions and guidelines: GRE configuration
When you configure a GRE tunnel, follow these restrictions and guidelines:
You must configure the tunnel source address and destination address at both ends of a tunnel. The tunnel source or destination address at one end must be the tunnel destination or source address at the other end.
As a best practice, do not configure the same tunnel source and destination addresses for local tunnel interfaces that use the same tunnel mode.
To ensure correct packet forwarding, identify whether the destination network of packets and the IP address of the local tunnel interface are on the same subnet. If they are not, configure a route reaching the destination network through the tunnel interface. You can configure the route by using one of the following methods:
Configure a static route, using the local tunnel interface as the outgoing interface of the route.
Enable BGP, IS-IS, or OSPF on both the tunnel interface and the interface connecting the private network. This allows BGP, IS-IS, or OSPF to establish a routing entry with the tunnel interface as the outgoing interface.
GRE encapsulation and de-encapsulation can decrease the forwarding efficiency of tunnel-end devices.