interface Tunnel1
 ip address 172.16.31.1 255.255.255.0
 no ip redirects
 ip nhrp map multicast 10.6.100.1
 ip nhrp map 172.16.31.6 10.6.100.1
 ip nhrp network-id 1
 ip nhrp nhs 172.16.31.6
 tunnel source Loopback0
 tunnel mode gre multipoint
 tunnel key 0