Dynamic Multipoint Virtual Private Network

Dynamic Multipoint Virtual Private Network (DMVPN)^[1] is a dynamic tunneling form of a virtual private network (VPN) supported on Cisco IOS-based routers, Huawei AR G3 routers^[2] and USG firewalls, and on Unix-like operating systems.

Benefits

DMVPN provides the capability for creating a dynamic-mesh VPN network without having to pre-configure (static) all possible tunnel end-point peers, including IPsec (Internet Protocol Security) and ISAKMP (Internet Security Association and Key Management Protocol) peers. DMVPN is initially configured to build out a hub-and-spoke network by statically configuring the hubs (VPN headends) on the spokes, no change in the configuration on the hub is required to accept new spokes. Using this initial hub-and-spoke network, tunnels between spokes can be dynamically built on demand (dynamic-mesh) without additional configuration on the hubs or spokes. This dynamic-mesh capability alleviates the need for any load on the hub to route data between the spoke networks.

Technologies

Generic Routing Encapsulation (GRE), RFC 1701, or multipoint GRE if spoke-to-spoke tunnels are desired
NHRP (next-hop resolution protocol), RFC 2332
IPsec (Internet Protocol Security) using an IPsec profile, which is associated with a virtual tunnel interface in IOS software. All traffic sent via the tunnel is encrypted per the policy configured (IPsec transform set)
An IP based routing protocol, EIGRP, OSPF, RIPv2, BGP or ODR (DMVPN hub-and-spoke only).^[3]

Internal routing

Routing protocols such as OSPF, EIGRPv1 or v2 or BGP are generally run between the hub and spoke to allow for growth and scalability. The Cisco-proprietary EIGRP is generally considered preferable as it is an advanced distance vector style protocol which better matches with the NBMA (Non-Broadcast Multi-Access) style network that DMVPN builds. Both EIGRP and BGP allow a higher number of supported spokes per hub.^[4]

Encryption

As with GRE tunnels, DMVPN allows for several encryption schemes (including none) for the encryption of data traversing the tunnels. For security reasons Cisco recommend that customers use AES.^[5]

References

External links

Cisco Systems
DMVPN Overview
Cisco DMVPN Design Guide
Dynamic Multipoint IPsec VPNs (Using Multipoint GRE/NHRP to Scale IPsec VPNs)
DMVPN Management
Open source NHRP protocol implementation

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