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  • DMVPN Phase 3 Single Hub – OSPF – Hub example

    Design & Configure

    DMVPN Phase 3 Single Hub – OSPF – Hub example

    Traffic Flow:

    • Packet is sent from Spoke’s 1 network to Spoke’s 2 network via Hub (according to routing table)
    • Hub routes packet to Spoke2 but in parallel sends back the NHRP Redirect message to Spoke1 containing information about suboptimal path to Spoke2 and tunnel IP of Spoke2
    • Spoke1 then issues the NHRP Resolution request of Spoke’s 2 NBMA IP address to NHS with destination IP of Spoke’s 2 tunnel, this NHRP Resolution request is sent targeted to Spoke2 via NHS (according to routing table) – it is normal hop by hop NHRP forwarding process
    • Spoke2 after receiving resolution request including NBMA IP of Spoke1 sends the NHRP Resolution reply directly to Spoke1 – Reply does not traverse the Hub!
    • Spoke1 after receiving correct NBMA IP of Spoke2 rewrites the CEF entry for destination prefix – this procedure is called NHRP Shortcut
    • Spokes don’t trigger NHRP by glean adjacencies but NHRP replies updates the CEF

     

    DMVPN Phase 3 and OSPF

    • Configure OSPF p2m type (all spokes are aware of whole topology)
    • Advertise spoke’s connected routers
    • Disable split horizon on hub (Spoke to Spoke prefix advertisement)
    • The one of OSPF limitation is single area routes summarization

    DMVPN Phase 3 OSPF Hub - Spoke Example configuration

     

    R1 – DMVPN Phase 3 – OSPF Hub configuration example:

    router ospf 111
    router-id 10.1.1.1
    summary-address 10.1.0.0 255.255.0.0
    network 10.1.1.0 0.0.0.255 area 0
    network 172.16.1.0 0.0.0.255 area 0
    POD1_R1#

    interface Tunnel0
    ip address 172.16.1.1 255.255.255.0
    no ip redirects
    ip mtu 1400
    ip nhrp authentication gmlabs
    ip nhrp map multicast dynamic
    ip nhrp network-id 111
    ip nhrp shortcut
    ip nhrp redirect
    ip ospf network point-to-multipoint
    tunnel source Loopback0
    tunnel mode gre multipoint
    tunnel key 123
    tunnel protection ipsec profile DMVPN_PROFILE
    end

    Author: Marcin Bialy
     
    Grandmetric