HVPN stands for Hierarchy VPN, which is a VPN technology applied to hierarchical networks. It is a type of BGP/MPLS IP VPN that uses a hierarchical network model instead of a flat network model. It distributes the PE functions across multiple devices that play different roles, such as UPEs, SPEs, and NPEs. This lowers the requirements on device performance level by level, improves network scalability, and facilitates the planning and design of large-scale networks.
HVPN works by using BGP to advertise VPN routes and MPLS to forward VPN packets on the service provider’s backbone network. However, unlike a flat BGP/MPLS IP VPN, where all PEs are on the same plane and have the same performance, HVPN divides the PEs into different levels and assigns different functions to them.
The following are the main elements of an HVPN:
- Underlayer provider edge (UPE): This is a type of PE directly connected to users. It mainly provides access services for users and does not need to maintain VPN routes or labels.
- Superstratum provider edge (SPE): This is a type of PE connected to UPEs and located on the core of a network. It manages and advertises VPN routes and labels for UPEs and other SPEs.
- Network provider edge (NPE): This is a type of PE connected to SPEs and located on the network side. It forwards VPN packets between SPEs and other NPEs.
On an HVPN, a UPE establishes a BGP session with an SPE to exchange VPN routes and labels. An SPE establishes BGP sessions with other SPEs and NPEs to exchange VPN routes and labels. An NPE establishes BGP sessions with other NPEs to exchange VPN routes and labels. A UPE also establishes an LDP session with an SPE to exchange transport labels. An SPE establishes LDP sessions with other SPEs and NPEs to exchange transport labels. An NPE establishes LDP sessions with other NPEs to exchange transport labels.
Some practical use cases of HVPN are:
- Network convergence: HVPN can help network operators to converge their multiple services onto a single IP backbone network, reducing the cost and complexity of network management and maintenance. HVPN can also enable seamless interworking between different types of services and networks.
- Service migration: HVPN can facilitate the migration of legacy services to new technologies without disrupting the existing customers or applications. HVPN can also provide backward compatibility and interoperability for legacy devices and protocols.
- Service innovation: HVPN can enable new types of services that combine the advantages of both Layer 2 and Layer 3 technologies, such as Ethernet VPNs, IP VPNs over Ethernet, and Layer 2 multicast. HVPN can also support flexible service provisioning and customization based on customer needs.