DMVPN - does tunnel or spoke initiate the GRE tunnel?

[Seth Beauchamp]

So just assuming its NHRP and GRE, no ipsec for this example. Does the NHRP exchange happen outside of GRE? Does the spoke initiate the GRE tunnel or does the hub initiate the GRE tunnel once it has the information for the spoke via NHRP?

[Rahul Govindan · Accepted solution]

NHRP exchange happens within GRE tunnel. Spoke always initiates the NHRP transaction as it has the Hub Logical and Public Access ip address static mapping (NHS and NBMA). Once the spoke registers with the hub, the hub learns of the logical to physical mapping and adds it in the NHRP table - allowing it to reply back.

A good explanation of the DMVPN exchange is given here:

http://blog.ine.com/2008/08/02/dmvpn-explained/

[Seth Beauchamp]

perfect, thanks.