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Large-Scale MPLS VPN Deployment Overview This chapter describes scalability issues encountered in large-scale MPLS VPN networks and presents a number of solutions that allow these networks to scale while growing. It includes the following topics: n MP-BGP Scalability Mechanisms n Partitioned Route Reflectors Objectives Upon completion of this chapter, you will be able to perform the following tasks: n Understand the MP-BGP scaling issues in large-scale MPLS VPN backbones n Describe the built-in scalability mechanisms n Design and implement networks using partitioned BGP route reflectors MP-BGP Scalability Mechanisms Objectives Upon completion of this section, you will be able to perform the following tasks: n Understand MP-BGP scaling issues n Describe the automatic filtering in MP-BGP n Describe the functions of the BGP Route Refresh feature n Describe the Outbound Route Filter feature and its benefits 2 Large-Scale MPLS VPN Deployment Copyright Ó 2000, Cisco Systems, Inc. Scaling •Existing BGP techniques can be used to scale the route distribution: route reflectors •Each edge PE router needs only the information for the VPNs it supports ▪Only routes for VRFs are configured on the PE router •Route-reflectors are used to distribute VPN routing information © 2000, Cisco Systems, Inc. www.cisco.com Chapter#4-5 A network designer that wants to design a scalable MPLS VPN solution is always faced with a number of scalability issues, several of them being related to the MPLS VPN architecture: n MPLS VPN uses internal BGP (IBGP) to propagate VPNv4 routes between PE routers. Default IBGP implementation requires a full-mesh of BGP sessions between PE routers—a design that is only appropriate for very small networks. n As the number of MPLS VPN customers grows, the PE routers have to store more and more customer routes (in traditional overlay VPN implementations, the customer routes are not seen by the provider routers—this issue is therefore not present in overlay VPN implementations). In very large MPLS VPN networks, providing connectivity to large customers, the number of routes that need to be stored by the PE routers exceeds the current scaling capabilities of Cisco IOS BGP implementation as well as memory and CPU resources of the PE routers. The IBGP full-mesh scalability roadblock is easily removed using traditional BGP scaling tools—BGP route reflectors and BGP confederations (both of them are described in the appropriate lessons of the BGP curriculum and their operations will not be discussed further in this section). Note BGP route reflectors are a preferred scalability tool for MPLS VPN networks and their positioning will be covered extensively in the next section. Copyright Ó 2000, Cisco Systems, Inc. Large-Scale MPLS VPN Deployment 3 The memory and CPU requirements imposed on a PE router by a large number of customer routes can be easily reduced if the PE router only stores routes relevant to the VPN customers connected to it and ignores all the other VPNv4 routes. The incoming route filtering had to be configured manually with early MPLS VPN implementation. To reduce the configuration complexity, Cisco IOS releases 12.0(7) T and 12.1 provide automatic filtering of incoming Multi-protocol BGP (MP-BGP) updates. 4 Large-Scale MPLS VPN Deployment Copyright Ó 2000, Cisco Systems, Inc. Auttomattiic MP--BGP Updates Filtering •The non-reflecting PE router discards any VPN-IPv4 route that hasn’t a route-target that is configured to be imported in any of the attached VRFs •This reduces significantly the amount of information each PE has to store •The size of the BGP table is proportional to the number of VRFs configured on the PE router © 2000, Cisco Systems, Inc. www.cisco.com Chapter#4-6 The automatic MP-BGP updates filtering uses a very simple algorithm—all VPNv4 routes received by a PE router that do not correspond to any VRF configured on the router are automatically ignored. This usually results in a significant reduction of VPNv4 BGP table on the PE router, as the size of the table becomes proportional to the number of VRFs configured on the PE router and not the overall size of the MPLS VPN network. Copyright Ó 2000, Cisco Systems, Inc. Large-Scale MPLS VPN Deployment 5 ... - tailieumienphi.vn
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