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

1. Dynamic Multipoint IPsec VPNs (Using Multipoint GRE/NHRP to Scale IPsec VPNs)
2. Huawei DSVPN Configuration
3. DMVPN Design Guide: Using a Routing Protocol Across the VPN
4. DMVPN Design Guide: Routing Protocol Configuration
5. DMVPN Design Guide: Best Practices and Known Limitations

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