DMVPN Phase 2 Configuration scenario

In DMVPN phase 1 we saw that there is no direct Spoke – Spoke communication. In phase 2 there will be a multipoint GRE tunnel interface on the spokes as well instead of point-point GRE tunnel. So we have direct spoke-spoke tunneling in phase 2. When a spoke router wants to reach to another spoke router it will send out a NHRP resolution request to HUB to find the NBMA address of the other spoke.

Let us use the same topology diagram as the one we used in our post for DMVPN phase 1 configuration as below:

Most of the configuration on the hubs and the Spoke will remain the same as in phase 1 except:

  • Now the Spokes will have Multipoint GRE tunnel interface.
  • There will be no manual destination configured on the spokes.

The first packet from spoke to spoke will traverse the hub after which we will see a dynamic tunnel created towards the spoke and the packet there onwards will reach directly the Spoke.

Configuration

R1:

interface Loopback0

ip address 1.1.1.1 255.255.255.255

!

interface Tunnel0

ip address 192.168.10.1 255.255.255.0

no ip redirects

no ip next-hop-self eigrp 100  #So that hub doesn’t list itself as the next hops for the routing updates of the spoke.

no ip split-horizon eigrp 100

ip nhrp authentication cisco

ip nhrp map multicast dynamic

ip nhrp network-id 10

tunnel source FastEthernet0/0

tunnel mode gre multipoint

!

interface FastEthernet0/0

ip address 9.9.0.1 255.255.255.0

!

router eigrp 100

network 1.1.1.1 0.0.0.0

network 192.168.10.0

R2:

interface Loopback0

ip address 2.2.2.2 255.255.255.255

!

interface Tunnel0

ip address 192.168.10.2 255.255.255.0

ip nhrp authentication cisco

ip nhrp map 192.168.10.1 9.9.0.1

ip nhrp map multicast 9.9.0.1

ip nhrp network-id 1

ip nhrp nhs 192.168.10.1

tunnel source FastEthernet0/0

tunnel mode gre multipoint

!

interface FastEthernet0/0

ip address 9.9.0.2 255.255.255.0

!

router eigrp 100

network 2.2.2.2 0.0.0.0

network 192.168.10.0

R3:

interface Loopback0

ip address 3.3.3.3 255.255.255.255

!

interface Tunnel0

ip address 192.168.10.3 255.255.255.0

ip nhrp authentication cisco

ip nhrp map 192.168.10.1 9.9.0.1

ip nhrp map multicast 9.9.0.1

ip nhrp network-id 1

ip nhrp nhs 192.168.10.1

tunnel source FastEthernet0/0

tunnel mode gre multipoint

!

interface FastEthernet0/0

ip address 9.9.0.3 255.255.255.0

!

router eigrp 100

network 3.3.3.3 0.0.0.0

network 192.168.10.0

Verification

On spokes we see only a single tunnel created towards the Hub.

R3#sh dmvpn

Legend: Attrb –> S – Static, D – Dynamic, I – Incomplete

N – NATed, L – Local, X – No Socket

# Ent –> Number of NHRP entries with same NBMA peer

NHS Status: E –> Expecting Replies, R –> Responding, W –> Waiting

UpDn Time –> Up or Down Time for a Tunnel

==========================================================================

Interface: Tunnel0, IPv4 NHRP Details

Type:Spoke, NHRP Peers:1,

 

# Ent  Peer NBMA Addr Peer Tunnel Add State  UpDn Tm Attrb

—– ————— ————— —– ——– —–

     1 9.9.0.1            192.168.10.1    UP 00:00:45     S

 

R2#sh dmvpn

Legend: Attrb –> S – Static, D – Dynamic, I – Incomplete

N – NATed, L – Local, X – No Socket

# Ent –> Number of NHRP entries with same NBMA peer

NHS Status: E –> Expecting Replies, R –> Responding, W –> Waiting

UpDn Time –> Up or Down Time for a Tunnel

==========================================================================

 

Interface: Tunnel0, IPv4 NHRP Details

Type:Spoke, NHRP Peers:1,

 

# Ent  Peer NBMA Addr Peer Tunnel Add State  UpDn Tm Attrb

—– ————— ————— —– ——– —–

     1 9.9.0.1            192.168.10.1    UP 00:00:45     S

The routing table on R2 shows the route for R3 is learnt directly via the R3 and vice versa.

R2#sh ip route | i 3.3.3.3

D        3.3.3.3 [90/28288000] via 192.168.10.3, 00:03:16, Tunnel0

R3#sh ip route | i 2.2.2.2

D        2.2.2.2 [90/28288000] via 192.168.10.2, 00:03:40, Tunnel0

We see the initial trace goes via the Hub and post that we will also see a Dynamic Spoke-Spoke Tunnel created:

R2#traceroute 3.3.3.3 source 2.2.2.2

Type escape sequence to abort.

Tracing the route to 3.3.3.3

VRF info: (vrf in name/id, vrf out name/id)

  1 192.168.10.1 96 msec 24 msec 24 msec

  2  *

    192.168.10.3 92 msec 28 msec

Next we see a Dynamic tunnel gets created between Spoke 1 and Spoke 2.

R2#sh dmvpn

Legend: Attrb –> S – Static, D – Dynamic, I – Incomplete

N – NATed, L – Local, X – No Socket

# Ent –> Number of NHRP entries with same NBMA peer

NHS Status: E –> Expecting Replies, R –> Responding, W –> Waiting

UpDn Time –> Up or Down Time for a Tunnel

==========================================================================

 

Interface: Tunnel0, IPv4 NHRP Details

Type:Spoke, NHRP Peers:2,

 

# Ent     Peer NBMA Addr        Peer Tunnel Add   State  UpDn Tm     Attrb

—– ————— ————— —– ——– —–

1              9.9.0.1                           192.168.10.1          UP     00:05:08      S

 1             9.9.0.3                       192.168.10.3      UP    00:01:06    D

R3#sh dmvpn

Legend: Attrb –> S – Static, D – Dynamic, I – Incomplete

N – NATed, L – Local, X – No Socket

# Ent –> Number of NHRP entries with same NBMA peer

NHS Status: E –> Expecting Replies, R –> Responding, W –> Waiting

UpDn Time –> Up or Down Time for a Tunnel

==========================================================================

 

Interface: Tunnel0, IPv4 NHRP Details

Type:Spoke, NHRP Peers:2,

 

# Ent  Peer NBMA Addr        Peer Tunnel Add      State      UpDn Tm   Attrb

—– ————— ————— —– ——– —–

1          9.9.0.1                           192.168.10.1              UP          00:05:36      S

  1         9.9.0.2                        192.168.10.2          UP        00:01:35     D

R2#sh ip nhrp

192.168.10.1/32 via 192.168.10.1

Tunnel0 created 00:07:20, never expire

Type: static, Flags: used

NBMA address: 9.9.0.1

192.168.10.3/32 via 192.168.10.3

Tunnel0 created 00:03:10, expire 01:56:51

Type: dynamic, Flags: router used

NBMA address: 9.9.0.3

We now further see that the trace towards R3 from R2 goes directly without traversing the Hub:

R2#traceroute 3.3.3.3 source 2.2.2.2

Type escape sequence to abort.

Tracing the route to 3.3.3.3

VRF info: (vrf in name/id, vrf out name/id)

  1 192.168.10.3 40 msec 20 msec 32 msec

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