L2VPN Service Module User Guide

The postman collection and YANG files can be accessed here

Overview

The goal of this project is to automate provisioning of Layer 2 Virtual Private Networks (L2VPN) on Service Provider (SP) routers. This is done by using the Frinx ODL controller which configures routers based on intent of the L2VPN service. The Frinx ODL controller translates the L2VPN service abstraction to network element configuration. L2VPN Service

A bit about L2VPN

Problem definition and L2VPN

A company needs to reconnect multiple sites with each other via an SP which provides L2 services to the company. The company’s sites needs to see each other as directly connected on L3. L2VPN offers a solution for those requirements.

The company has two different sites and they are both connected to the Service Provider using an L2 connection. They need to interconnect two of their sites. Two company's sites connected to SP

In this case L2VPN provides site-to-site connectivity and the SP network behaves as a wire between the company’s sites. The company’s routes are exchanged via the SP network. Solution with L2VPN between sites.

Terminology

These terms are usually used in the L2VPN domain:

  • Customer Edge (CE) device – router at customer site connected to SP
  • Provider Edge (PE) device – router at the edge of the SP network which provides connectivity for CE
  • Provider (P) device – core router on the SP network providing connectivity among PE routers

Terminology in picture

L2VPN types

There are two main types of L2VPN:

  • point-to-point
  • point-to-multipoint

These types have many implementations. The Frinx ODL distribution supports Virtual Private Wire Service (VPWS) implementation.

VPWS

VPWS (Virtual Private Wire Service) is the simplest form for enabling Ethernet services over MPLS. It is also known as ETHoMPLS (Ethernet over MPLS), or VLL (Virtual Leased Line). VPWS is point-to-point L2VPN which usually uses MPLS in core networks for signaling and creates pseudo-wires on PE routers for separation of L2 connections. L2 connections are identified by interface or VLAN. The picture below shows an MPLS core network with pseudo-wires on PEs for each VPN which are identified by VLAN. VPWS example

L2VPN Provider

L2VPN Provider is an implementation which automatically provisions L2VPN on PE routers based on intended L2VPN service. It exposes a domain specific API for L2VPN manipulation and declarative configuration “what vs how”. L2VPN Provider supports network wide transactions which are transactions on top of multiple devices. Rollback of a network wide transaction means rollback of configuration on each device which was a part of the conifiguration. The rollback of a network wide transaction is done automatically if there is failed configuration on at least one device.

Use Case Specification

L2VPN Provider can be used on a network where:

  • VPWS L2VPN is needed
  • VLAN is used for pseudo-wire selection
  • MPLS encapsulation is used in SP core

Use case example

Architecture

L2VPN Provider is composed of multiple components. The high level architecture is shown in the picture below.

Architecture

An external application modifies ietf-l2vpn in CONF DS. L2VPN can be configured on nodes which are read from l2vpn-provider-edge-topology. When all changes are done, the external application calls RPC commit-l2vpn. The RPC reads ietf-l2vpn from CONF DS (the intended state) and from OPER DS (the actual state). Diff is created based on intended and actual state. This diff is configured inside network wide transaction on the necessary PE routers by using particular Network Element Plugins. If configuration of routers is successful then a new ietf-l2vpn is stored to OPER DS and RPC output is returned with status “complete”. In case configuration on one of the devices fails, the rollback of the network wide transaction starts and if the rollback is successful then RPC output has status “commit-failed-rollback-complete”, otherwise the status is “inconsistent”. The architecture can be extended very easily because Network Element Plugin needs to implement only NEP SPI, rollback, and network element registration. IOS NEP from the picture is not yet implemented.

As was mentioned, NEP registers network elements to L2VPN Provider. L2VPN Provider stores network elements as nodes to abstract topology l2vpn-provider-edge-topology and this topology is a source of nodes which can be used for L2VPN configuration.

API description

The API is described using YANG modules. An external application can consume the API via RESTCONF, NETCONF, or JAVA. The L2VPN service module provides domain specific abstraction where the abstraction describes attributes of VPNs and sites instead of configuration of network elements. The FRINX ODL Distribution translates the abstraction to network element configuration.

ietf-l2vpn@2017-08-02.yang

Original YANG is from RFC draft – YANG Data Model for MPLS-based L2VPN. This YANG module is modified due to compatibility with OpenDaylight and is extended with L2VPN Provider elements – see the modified YANG module ietf-l2vpn@2017-08-02.yang here

The YANG module contains 2 root statements and one RPC:

  • container l2vpn – represents intended state stored in CONF DS and actual state stored in OPER DS
  • container l2vpn-state – not used in current implementation
  • rpc commit-l2vpn – configures intent of L2VPN service. The output of RPC is the result of service configuration.

The following YANGs are modified due to compatibility with OpenDaylight: ietf-mpls, ietf-routing, ietf-routing-types, all accessible here.

Network Element Plugin

Network Element Plugin (NEP) is a unit which implements SPI from the L2VPN Provider. This NEP is device API specific and is responsible for:

  • announcement of discovered device (PE) to the L2VPN Provider
  • translation between SPI Data Transfer Objects (DTO) and device configuration
  • rollback of configuration on a device

IOS-XRv Network Element Plugin

This plugin configures L2VPN on IOS-XRv using NETCONF. It listens on topology-netconf and announces PE capable devices to the L2VPN Provider. Rollback on a device is done automatically using the “Rollback-on-Error” capability.

IOS-XRv NEP

IOS-XRv NEP listens on nodes in topology-netconf. When a new IOS-XRv device is connected to Frinx ODL it appears as a new node in topology-netconf and IOS-XRv registers that node as PE to L2VPN Provider. If L2VPN Provider calls SPI in order to configure PEs via the IOS-XRv NEP, NETCONF is used for device configuration.

Here is an example of L2VPN configuration on IOS-XRv (parameters encapsulated in ** are specific for VPN or site):

Mock Network Element Plugin

The purpose of this plugin is to mock functionality of the Network Element Plugin. It is mainly use for testing when you do not need to connect real devices. Mock NEP

The Mock NEP listens on nodes from mock-pe-topology. When a node is created, the NEP registers this node as a PE node to the L2VPN Provider. When the L2VPN Provider calls the SPI which Mocks NEP implements, intead of configuration of real devices, the SPI DTOs are logged.

Limitations

Implementation of L2VPN provider does not support all statements in ietf-l2vpn@2017-08-02.yang. All supported elements are listen in the postman collection. L2VPN Provider does not support reconciliation, therefore only L2VPNs created via L2VPN Provider are visible through API.

Other limitations:

  • only MPLS encapsulation is supported
  • only VLAN can be used between CE and PE for pseudo-wire selection
  • pre-configured MPLS among PEs must exist

User-facing features

frinx-l2vpn-iosxrv

Karaf installation:

Description:
Installs L2VPN Provider with IOS-XRv NEP and NETCONF connector. This feature is NEP for IOS-XRv devices.

frinx-l2vpn-testing

Karaf installation:

Description:
Installs L2VPN Provider with Mock NEP and RESTCONF. This feature can be used for testing and demonstration purposes where real PE devices are not available.

Feature Guide
Feature introduced in FRINX 2.3.1 VPN service module implementation with support for L2VPN and IOS XR (Version 6.1.2) NEP via NETCONF