NHRP: No node found. Tunnel IP addr The NHS may immediately reply to the client. Again, R2 replies back across the hub and send a Resolution Request packet: first, directly R3 — this attempt fails - then it sends the resolution request to the NHS. NHRP: No need to delay processing of resolution event nbma src As we remember, each NHRP entry has countdown expire timer, initialized from the registration hold-time.
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NHRP: No node found. Tunnel IP addr The NHS may immediately reply to the client. Again, R2 replies back across the hub and send a Resolution Request packet: first, directly R3 — this attempt fails - then it sends the resolution request to the NHS. NHRP: No need to delay processing of resolution event nbma src As we remember, each NHRP entry has countdown expire timer, initialized from the registration hold-time. This will effectively tear down the spoke-to-spoke tunnel.
Firstly, this mode requires all the spokes to have complete routing information with the next-hop preserved. This may limit scalability in large networks, since not all spokes may accept full load of routing updates.
Actually, the second feature directly implies the first limitation. As we noted, the no ip next-hop-self eigrp command is required to make spoke-to-spoke tunnels work with CEF. However, they added the command only in IOS version Actually, there are few ways. This is because every hub must form OSPF adjacencies with all spokes. Such limitation is not acceptable in large installations, but still works fine in smaller deployments.
However, there is one final workaround, which is probably the one you may want to use in the current CCIE lab exam — disable CEF on spokes. This is a very interesting case per se, and we are going to see now NHRP works with process switching. Now R3 sees R3 sees the route behind R2 as reachable via R1 Rack1R3 show ip route This is opposed to CEF behavior that would only resolve the next-hop for " In addition, R1 forwards the data packet from R1 to R2, using its routing table.
Obviously, the data packet will arrive to R2 a little bit faster, since NHRP requires more time to process and forward the request. Since the NHS has no information on " The local router performs lookup for
Understanding Cisco DMVPN
Because mGRE tunnels do not have a tunnel destination defined, they cannot be used alone. These include: Simplified Hub Router Configuration. No more multiple tunnel interfaces for each branch spoke VPN. No matter how many Spoke routers connect to the Hub, the Hub configuration remains constant. Spoke routers can use dynamic public IP Addresses. Spoke routers are able to dynamically create VPN Tunnels between them as network data needs to travel from one branch to another. Lower Administration Costs.
Understanding Cisco Dynamic Multipoint VPN - DMVPN, mGRE, NHRP
Cisco DMVPN uses a centralized architecture to provide easier implementation and management for deployments that require granular access controls for diverse user communities, including mobile workers, telecommuters, and extranet users. Dynamic discovery of IPsec tunnel endpoints and crypto profiles: eliminates the need to configure static crypto maps defining every pair of IPsec peers, further simplifying the configuration. Routing Protocol: used to learn network between hub and spokes. The hub maintains an NHRP database of the public interface addresses of the each spoke. Each spoke registers its real address when it boots; when it needs to build direct tunnels with other spokes only on phase2 and phase3 , it queries the NHRP database for real addresses of the destination spokes.
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