NHRP Entry Points to My Own Router

[eitanbenari4]

I'm working with a DMVPN Phase 3 setup, and I noticed something strange in the output of show ip nhrp on my own router (R4).
This is the output:

R4#sh ip nhrp
10.0.0.1/32 (overlay) via 10.0.0.1
Tunnel0 created 00:15:18, never expire
Type: static, Flags: used
NBMA address: 200.0.0.4
10.0.0.2/32 (overlay) via 10.0.0.2
Tunnel0 created 00:02:11, expire 01:57:48
Type: dynamic, Flags: router nhop
NBMA address: 200.0.0.2
10.0.0.4/32 (overlay) via 10.0.0.4
Tunnel0 created 00:02:11, expire 01:57:48
Type: dynamic, Flags: router unique local
NBMA address: 200.0.0.0
(no-socket) 

R4#sh ip int br
Ethernet0/0 200.0.0.0 YES manual up up
Tunnel0 10.0.0.4 YES manual up up

why on ROUTER 4 i see entry for its own interface tunnel address 10.0.0.4 and physical address 200.0.0.0 in the show ip nhrp command? 

[M02@rt37 · Accepted solution]

Hello @eitanbenari4 

It is normal. You see the 10.0.0.4/200.0.0.0 entry because routeur R4 registers itself with the NHRP database as part of DMVPN Phase 3*. The entry is flagged as "unique local", indicating it's the local router’s own address mapping — and it is necesary for correct NHRP operations...

*DMVPN phase 3 uses spokes that now respond to NHRP Resolution Requests. This means that the Hub is no longer the only one holding NHRP information.

[eitanbenari4]

Hey thank you! can you please explain to me the basic differences between phase 2 and phase 3. 

[M02@rt37]

You're so welcome @eitanbenari4 

Phase 2 allows for dynamic Spoke-to-spoke tunnels. All routers are configured with mGRE tunnels, and the Spokes have the NHS hub configured statically. When a spoke needs to send a packet via a Next-Hop on the mGRE cloud, it sends an NHRP Resolution Request packet to the Hub/NHS. The Hub responds with an NHRP Resolution Reply packet from its cache and the Spoke can then know the NBMA address of another Spoke and contact it directly.

For Phase3 , as in Phase 2, mGRE tunnels are used on both the hub and the spokes, but we're adding an NHRP redirection that allows the Data Plane of spoke-to-spoke conversations to directly reach the spokes without going through the hub (without requiring CEF resoluton). NRHP Pphase 3 uses spokes, which now respond to NHRP Resolution Requests. This means that the hub is no longer the only one holding NHRP information.

--source: https://www.networklife.net/2014/10/dmvpn-phase-12-et-3/