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JUNOS Cookbook by Aviva Garrett

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Chapter 15. VPNs

Introduction

Customers want their internal networks to function as a single network so all employees can communicate and access corporate services regardless of location. Network service providers can create private networks that join all a customer's sites into a single network. These sites can be connected with point-to-point links, including leased lines, Frame Relay circuits, ATM circuits, and GRE tunnels that allow customer routers to peer with each other. This model of overlaying a private network on top of the public Internet leaves the network provider with the responsibility of designing and operating virtual backbones for all their customers. This solution presents several problems. Scaling issues will arise because a network provider must support more customers and more virtual backbones for an ever-increasing number of customers. When a customer adds a new site, the network provider will need to reconfigure all the existing sites and, as the number of sites grows, maintaining the private network will become more complex.

One solution to the scaling issues associated with private networks are BGP-MPLS VPNs, defined in RFC 2547bis and sometimes called Layer 3 VPNs because of the BGP component. Layer 3 VPNs can support thousands of VPNs with hundreds of sites per VPN and can support overlapping address space. BGP-MPLS VPNs set up private networks that run over the shared infrastructure of the Internet. As with private networks, VPNs interconnect geographically ...

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