DMVPN Phase 1 Configuration scenario

DMVPN stands for Dynamic Multipoint VPN. It is a technique where we can build a VPN network on hub-spoke topologies dynamically without having the need to configure the devices statically. DMVPN also supports IPsec encryption and hence is a popular technique for building tunnels over internet connectivity thus acting as an alternative to MPLS connectivity solutions. DMVPN is usually deployed in HUB and Spoke topologies. Hub has a single multipoint tunnel interface and all the spoke sites have a single point-point tunnel interface with Hub site.

DMVPN has three phases and in this post we will discuss the first DMVPN phase. In 1st phase there can’t be any Spoke to spoke communication directly. Any spoke that needs to speak to another spoke site has to go through a Hub site in phase 1.

We will use the simple topology as below to configure the Multipoint tunnels and bring the EIGRP neighborship up between the Spoke and Hub sites.

Topology

In our topology R1 is the router at Hub site and R2 and R3 are the routers at the two spoke sites. R2 and R3 form a GRE tunnel with HUB over its multipoint GRE tunnel interface.

Once the tunnels between the Spoke and the Hub sites are up we will run EIGRP over the Tunnels and should be able to see the communication happening between the two spoke sites via the Hub site.

 

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 split-horizon eigrp 100  # As EIGRP split horizon is enabled by default and if we don’t disable this the Hub router wont advertise the routes learnt from Spoke 1 to Spoke2 and vice versa.

ip nhrp authentication cisco # Optional but we configure to authenticate our NHRP traffic

ip nhrp map multicast dynamic #this command tells the hub router where to forward multicast packets to. Since the IP addresses of the spoke routers are unknown, we use dynamic to automatically add their IP addresses to the multicast destination list when the spokes register themselves.

ip nhrp network-id 10 # ID is used to differentiate between multiple DMVPN networks, usually kept same on all routers.

tunnel source FastEthernet0/0

tunnel mode gre multipoint # Default tunnel mode is p2p GRE so enable multipoint GRE.

!

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 #Creating Static mapping between HUBs tunnel and NBMA address

ip nhrp map multicast 9.9.0.1

ip nhrp network-id 1

ip nhrp nhs 192.168.10.1 #Mention the NHRP server which in our case is hub router.

tunnel source FastEthernet0/0

tunnel destination 9.9.0.1

!

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 destination 9.9.0.1

!

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 the hub site we see the two Spoke sites are registered

R1# 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:Hub, NHRP Peers:2,

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

—– ————— ————— —– ——– —–

1 9.9.0.2            192.168.10.2    UP 01:02:37     D

1 9.9.0.3            192.168.10.3    UP 01:01:56     D

R1#sh ip nhrp

192.168.10.2/32 via 192.168.10.2

Tunnel0 created 01:03:17, expire 01:36:42

Type: dynamic, Flags: unique registered used

NBMA address: 9.9.0.2

192.168.10.3/32 via 192.168.10.3

Tunnel0 created 01:02:36, expire 01:37:22

Type: dynamic, Flags: unique registered used

NBMA address: 9.9.0.3

On the spoke we see the NHS server showing as the HUB router:

R2#  sh ip nhrp nhs detail

Legend: E=Expecting replies, R=Responding, W=Waiting

Tunnel0:

192.168.10.1  RE priority = 0 cluster = 0  req-sent 9  req-failed 0  repl-recv 3 (00:26:19 ago)

Next we see the Hub has formed EIGRP neighborship with both the spoke sites:

R1# sh ip eigrp neighbors

EIGRP-IPv4 Neighbors for AS(100)

H   Address                 Interface              Hold Uptime   SRTT   RTO  Q  Seq

(sec)         (ms)       Cnt Num

0   192.168.10.2            Tu0                      12 00:36:51   56  1470  0  8

1   192.168.10.3            Tu0                      13 00:43:37   41  1470  0  6

R1#sh ip route eigrp

Codes: L – local, C – connected, S – static, R – RIP, M – mobile, B – BGP

D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area

N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2

E1 – OSPF external type 1, E2 – OSPF external type 2

i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2

ia – IS-IS inter area, * – candidate default, U – per-user static route

o – ODR, P – periodic downloaded static route, H – NHRP, l – LISP

+ – replicated route, % – next hop override

Gateway of last resort is not set

2.0.0.0/32 is subnetted, 1 subnets

D        2.2.2.2 [90/27008000] via 192.168.10.2, 00:37:11, Tunnel0

3.0.0.0/32 is subnetted, 1 subnets

D        3.3.3.3 [90/27008000] via 192.168.10.3, 00:43:57, Tunnel0

Both the spokes learn route about each other via the Hub site as follows:

R2#sh ip route | i 3.3.3.3

D        3.3.3.3 [90/28288000] via 192.168.10.1, 00:37:25, Tunnel0

R3#sh ip route | i 2.2.2.2

D        2.2.2.2 [90/28288000] via 192.168.10.1, 00:37:33, Tunnel0

We see the trace also goes from Spoke > Hub > Spoke as follows:

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 56 msec 44 msec 24 msec

2 192.168.10.3 40 msec 56 msec 76 msec

Please follow and like us:

Related Post

No Responses

Add Comment

Social Media Auto Publish Powered By : XYZScripts.com
Select your currency