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How Does VPRN Work?

Author: gokhankosem, on 16 Oct 17 - 0 Comments
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How Does VPRN Work?

Basically in a VPRN Architecture, there is a Service Provider Network and there are multiple branches of multiple customers. Service Provider consist of P and PE devices and every branch of a customer has a CE device to connect to the Service Provider Network. These connection points are PE routers. PE routers are also the routers, that L3 VPN (VPRN) Services are defined.

In VPRN Architecture, customer routers (CE) are connected to the Service Provider Edge Routers (PE). In the Provider Edge Routers there is a specific IP forwarding table (VRF Table) for each customer (or each VPRN). This is the table created after VPRN (L3 VPN)definion.

A VRF Table is a specific Routing Table belongs to a specific VPRN. There are multiple VRF tables in a PE Router. Beside VRF tables, PE Routers also has a Default Forwarding Table.

In VPRN, customers can manage their IP addressing. They also manage CE devices and responsible from the routing inside their network. Customers use their own routing protocols. They provide the routing information of their private network to the Service Provider. For route advertisements, it can use same or different ip routing protocols between them and Service Provider Edge Router (PE Router).

Service Provider has already a routed network. And every Service Provider use an apprepriate routing protocol for their network. P and PE devices use this routing protocol inside the core network.

VPRN Service is a Layer 3 Service that provides end-to-end communication of customer branches over Service Provider IP/MPLS network. This Service is defined in PE devices of Service provider and for end-to-end service delivery, LSP tunnels are build between the PE devices. In this LSP tunnels, customer traffic is pass through the Service Provider network.

After explainning general VPRN process, let’s check VPRN process detailly. Here, we will explain VPRN with two main activities. These activities are Control Plane Activities and Data Plane Activities.

VPRN Control Plane and Data Plane

There are two planes in VPRN services. One is control Plane where VPRN prefixes and customer network is identified. And the other is Data (Forwarding) Plane where the data is transported and forwarded according to the VPN service label.

In control plane, Customer routes are advertised to the PE routers. And In PE routers they are stored in the VRF Tables. Between the PE routers, CE routes are exchanged. This is done after adding the Route Distinguisher to the routes. This allows using overlapping IP blocks. At the remote PE, the destination Customer router is identified by Route Targets and the routes are propagated to the destination Customer router. You can see this control plane process of VPRN below:

Alcatel-Lucent, VPRN Control Plane

VPRN Control Plane

In data plane, Customer routers send IP packets to the PE router. In PE router, LSP Label(Outer Label) and VPN Label(Inner Label) is added to the IP packet. In provider network, this packet is label switched. Only Outer Label is changed and Inner Label does not change. Because, Provider routers are unaware about Service.At the remote PE, the labels are removed and the traffic is propagated to the exact point according to the VPN Label. You can see the data plane provess of VPRN below:

Alcatel-Lucent, VPRN Data Plane

VPRN Data Plane

Here, we have talked about basic VPRN process. We will also explain the summary of Control Plane and Data Plane activities of VPRN. We will talk about these Contol Plane and Data Plane detailly in the next articles.

You can continue with other VPRN Articles…

VPRN (Virtual Private Routed Network) – VPRN Overview
VPRN (Virtual Private Routed Network) – VPRN Labels
VPRN (Virtual Private Routed Network) – How Does VPRN Work?
VPRN (Virtual Private Routed Network) – VPRN Control Plane Activities
VPRN (Virtual Private Routed Network) – VPRN Data Plane Activities
VPRN (Virtual Private Routed Network) – Alcatel-Luncet (Nokia) VPRN Configuration

General Alcatel-Lucent (Nokia) VPN Service Articles…

Alcatel-Lucent L2 VPN and L3 VPN Services – Part 1 (Service Terms and Service Creation Steps)
Alcatel-Lucent L2 VPN and L3 VPN Services – Part 2 (Service Types)
Alcatel-Lucent L2 VPN and L3 VPN Services – Part 3 (Network Preparation)
Alcatel-Lucent L2 VPN and L3 VPN Services – Part 4 (Tunnel Structure)

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About the Author
Gokhan Kosem is a telecommunation and network engineer. His ambition to IP networks and end-to-end system installation made him to prepare this web-site. By sharing his experiences about various networking protocols beside different system installation experiences and Cisco, Juniper, Alcatel-Lucent devices configurations, he is aimed to be helpful for his collegues in all over the world. He is currently lives in Istanbul, Turkey.

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