3

These two commands seems similar when I configure a DMVPN Spoke. What is the difference?

interface Tunnel1
 ip address 192.168.88.2 255.255.255.248
 no ip redirects
 **ip nhrp map 192.168.88.1 10.0.1.1**
 ip nhrp map multicast 10.0.1.1
 ip nhrp network-id 1
 **ip nhrp nhs 192.168.88.1**
 tunnel source FastEthernet0/0
 tunnel mode gre multipoint
1

Thanks to PacketLife.net:

Assuming router foo is configured as the Next-Hop Server, has a physical interface with IP address 10.0.1.1, and a tunnel interface with IP address 192.168.88.1 whose source is the 10.0.1.1 interface, then

ip nhrp nhs 192.168.88.1 designates router foo as the Next-Hop Server.

ip nhrp map 192.168.88.1 10.0.1.1 statically maps 192.168.88.1 to foo's physical address.

Basically, it's a chicken-and-the-egg problem. Normally, you'd query the NHS for a tunnel endpoint's physical address, but you need to know the NHS's physical address in order to query it. Thus, the static mapping.

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