NHRP PROTOCOL FOR DMVPN ARCHITECTURE
Imola includes NHRP protocol that, in Hub & Spoke systems (Imola plays the Spoke role) allows
routers with Hub role to activate GRE tunnels dynamically, without configuring them in advance.
The main task of the NHRP protocol in this case is to communicate to the Hub the physical address,
which should be used to establish the tunnel. It is compliant to the Cisco's Dynamic Multipoint VPN
(DMVPN)
For example: the Hub has IP address 85.34.166.17 and the Spoke (an Imola router) has IP address
217.201.121.1.
The Imola GRE tunnel IP address is 192.168.10.11/24 and the Hub GRE tunnel IP address will be
192.168.10.1/24
On the router Imola the following commands are set:
set gre tunnel 0 name tunnel 0
set gre tunnel 0 multicast
set gre tunnel 0 ttl 64
set gre tunnel 0 tunnel-source 217.201.121.1
set gre tunnel 0 tunnel-destination 85.34.166.17
set gre tunnel 0 tunnel-address 192.168.10.11/24
set gre tunnel 0 on
set nhrp interface tunnel 0
set nhrp map 192.168.10.1/24 85.34.166.17
set nhrp holding-time 300
set nhrp on
Enabling the NHRP protocol on Imola will ensure that the GRE tunnel required will be created
dynamically. The holding time parameter specifies how long the tunnel is still valid. When it
expires, the activation request will be renewed.
With the command show nhrp the NHRP status will be displayed:
root@IMOLA> show nhrp nbma 85.34.166.17
Interface: tunnel 0
Type: static
Protocol-Address: 192.168.10.1/24
NBMA-Address: 85.34.166.17
Flags: up
or:
root@IMOLA> show nhrp schedule
Timeout: 10
Description: Admin connection timeout for fd 11
Timeout: 147
Description: Renew registration for 192.168.10.1/24 nbma 85.34.166.17 dev tunnel 0
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