Say we have a hierarchical DMVPN environment. We have a west region consisting of a hub and 2 spokes, an east region with a hub and 2 spokes and a central hub tying it all together. The west and east hubs would each have 2 tunnel interfaces - tunnel0 facing their local region and tunnel1 facing up tot he central hub. The central hub would simply have tunnel0. Everything would be configured with the same NHRP ID globally.
I'm having a hard time understanding the control plan specifics of how NHRP allows dynamic spoke to spoke tunnels between regions. I understand the phase 3 concept (shortcuts and redirects) in a single region, but can't piece it together for multiple regions. Basically, what I am struggling with is this - If I am a host off a spoke in the west region and I wish to reach a host off a spoke in the east region, ultimately what I want is a dynamic spoke to spoke tunnel. We will call these spoke 1 and spoke 2 here. - Spoke 1 gets the packet and routes it to the west hub. - The west hub receives it on say tunnel0 and routes it out tunnel1 facing up towards the central hub. - The central hub only has a single tunnel0 interface. It receives the packet in the same interface it hairpins it back out which from what I understand is what triggers the NHRP redirect back towards the west hub. Ultimately though, we need the NHRP redirect message to actually hit the original spoke so that the spoke in west can initiate an NHRP resolution request for the spoke in East. This is where I get lost. How does the redirect get to the spoke in west to begin with? My thought is that perhaps the west hub actually sends the NHRP redirect to the spoke when it sends a packet out another tunnel interface configured with the same NHRP ID as the tunnel interface that received the packet. What am I missing? -- Regards, Joe Astorino CCIE #24347 http://astorinonetworks.com "He not busy being born is busy dying" - Dylan
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