30: Dynamic Multipoint Virtual Private Network (DMVPN)
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© Virtual Access 2017
GW1000 Series User Manual
Issue: 1.9
Page 283 of 350
30.3.2
Scenario 2
Spoke1 is in a private (NAT-ed) network, spoke2 and hub are in public network.
Figure 142: Network diagram for DMVPN spoke behind NAT
Spoke1 sends an NHRP registration request to the hub.
Hub receives this request and compares the source tunnel address of the spoke
with the source of the packet.
Hub sends an NHRP registration reply with a NAT extension to spoke1.
The NAT extension informs spoke1 that it is behind the NAT-ed device.
Spoke1 registers its pre- and post-NAT address.
When spoke1 wants to talk to spoke2, it sends an NHRP resolution request to the
hub.
Hub checks its cache table and forwards that request to spoke2.
Spoke2 caches spoke1’s GRE pre- and post-NAT IP address and sends an NHRP
resolution reply via the hub.
Spoke1 receives the NHRP resolution reply and updates its NHRP table with
spoke2 information. It initiates a VPN IPSec connection to spoke2.
When the IPSec tunnel is established, spoke1 and spoke2 can send traffic directly
to each other.
Note
: if an IPSec tunnel fails to be established between the spokes then packets
between the spokes are sent via the hub.