Hello
On configuration front, only the following to be done
NJ Router:
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tunnel source to be changed to new IP address
IP address of the physical interface towards the IP & Routing
All Spoke Routers: in the tunnel
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no Ip nhrp map multicast <old Physical IP at NJ>
no ip nhrp map <NJ tunnel IP> <old Physical IP at NJ>
Ip nhrp map multicast <New Physical IP at NJ>
ip nhrp map <NJ tunnel IP> <New Physical IP at NJ>
From the migration point of view, What I would suggest is start from one of the Spoke router and remove its configuration related to NJ and make sure that it works with Australia Hub, then you can do the migration of NJ router ( All other spokes should fall back to Australia) and Join the previous Spoke to test . If that is successful, you can plan for the migration of the all other spokes
Hope this helps
Harish.
