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Routing & Switching · Advanced

Multipoint GRE (mGRE)

A GRE tunnel interface with no fixed destination that can reach many endpoints, used as the DMVPN overlay.

Definition

mGRE interfaces rely on NHRP to map tunnel (overlay) addresses to NBMA (underlay) addresses dynamically. A single interface on the hub serves all spokes, and spokes also use mGRE in DMVPN Phase 2 and 3 to build direct tunnels.

Example

tunnel mode gre multipoint

Exam tip

Point-to-point GRE on spokes limits DMVPN to Phase 1 hub-and-spoke only.

Related terms