Gre

IP Tunnels Tunnels encapsulate one protocol inside another, creating a virtual point-to-point link across a network that wouldn’t otherwise carry that traffic. The encapsulating network is called the underlay; the encapsulated traffic and the logical topology it creates is called the overlay. Both GRE and IP-IP are stateless — they hold no session state and provide no encryption or reliability guarantees. Common use cases: Carry IPv6 traffic across an IPv4-only core (6in4) Carry IPv4 traffic across an IPv6-only core (4in6) Extend IGP adjacencies across a WAN that doesn’t support multicast Tunnel MPLS across a non-MPLS network Bridge Layer 2 domains across a routed network Tunnel Concepts Underlay vs Overlay: ...