In what kind of condition that the tunnel interface need to be configured on the router?

Hi,

The basic use of tunnel interface (GRE) on router between two locations is to route private ip blocks through public ip network.GRE tunnel interfaces are used to facilitate encapsulation of traffic that would otherwise not be routable,it may be private addresses and also be non-IP traffic (IPX, AppleTalk, etc.), or multicast traffic such as dynamic routing protocols (OSPF, EIGRP, etc.).GRE encapsulation results in an additional IP header (tunnel source IP, and tunnel destination IP).

Hope to Help !!

Ganesh.H

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