Post on 31-Mar-2015
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-1
MPLS VPN Technology
Introducing the MPLS VPN Routing Model
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-2
Outline
• Overview
• MPLS VPN Routing Requirements
• What Is the MPLS VPN Routing Model?
• Existing Internet Routing Support
• Routing Tables on PE Routers
• Identifying End-to-End Routing Update Flow
• Route Distribution to CE Routers
• Summary
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-3
MPLS VPN Routing Requirements
• CE routers have to run standard IP routing software.
• PE routers have to support MPLS VPN services and IP routing.
• P routers have no VPN routes.
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-4
MPLS VPN Routing:CE Router Perspective
• The CE routers run standard IP routing software and exchange routing updates with the PE router.
– EBGP, OSPF, RIPv2, EIGRP, and static routes are supported.
• The PE router appears as another router in the C-network.
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-5
MPLS VPN Routing:Overall Customer Perspective
• To the customer, the PE routers appear as core routers connected via a BGP backbone.
• The usual BGP and IGP design rules apply.
• The P routers are hidden from the customer.
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-6
MPLS VPN Routing:P Router Perspective
• P routers do not participate in MPLS VPN routing and do not carry VPN routes.
• P routers run backbone IGP with the PE routers and exchange information about global subnetworks (core links and loopbacks).
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-7
MPLS VPN Routing:PE Router Perspective
PE routers:• Exchange VPN routes with CE routers via per-VPN routing protocols
• Exchange core routes with P routers and PE routers via core IGP
• Exchange VPNv4 routes with other PE routers via MP-IBGP sessions
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Support for Existing Internet Routing
PE routers can run standard IPv4 BGP in the global routing table:
• PE routers exchange Internet routes with other PE routers.
• CE routers do not participate in Internet routing.
• P routers do not need to participate in Internet routing.
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-9
Routing Tables on PE Routers
PE routers contain a number of routing tables:
• The global routing table contains core routes (filled with core IGP) and Internet routes (filled with IPv4 BGP).
• The VRF tables contains routes for sites of identical routing requirements from local (IPv4 VPN) and remote (VPNv4 via MP-BGP) CE routers.
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-10
End-to-End Routing Update Flow
PE routers receive IPv4 routing updates from CE routers and install them in the appropriate VRF table.
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PE routers export VPN routes from VRF tables into MP-BGP and propagate them as VPNv4 routes to other PE routers.
End-to-End Routing Update Flow (Cont.)
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-12
End-to-End Routing Update Flow:MP-BGP Update
An MP-BGP update contains these elements:• VPNv4 address
• Extended communities (route targets, optionally SOO)
• Label used for VPN packet forwarding
• Any other BGP attribute (for example, AS path, local preference, MED, standard community)
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-13
• The receiving PE router imports the incoming VPNv4 routes into the appropriate VRF based on route targets attached to the routes.
• The routes installed in the VRFs are propagated to the CE routers.
End-to-End Routing Update Flow (Cont.)
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-14
Route Distribution to CE Routers
• A route is installed in the site VRF if it matches the import route target attribute.
• Route distribution to CE sites is driven by the following:
–Route targets
–SOO attribute if defined
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-15
What Is Multi-VRF CE (VRF-Lite)?
• Multi-VRF CE (VRF-lite) is an application based on VRF implementation.
– VRF-lite supports multiple overlapping and independent VRFs on the CE router.
• The CE router separates traffic between client networks using VRFs.
• There is no MPLS functionality on the CE router.
– No label exchange between the CE and PE router.
– No labeled packet flow between the CE and PE router.
• Any routing protocol supported by normal VRF can be used in a Multi-VRF CE implementation.
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-16
Summary
• In MPLS VPNs:
– CE routers run standard protocols (static, RIPv2, OSPF, EIGRP, EBGP) to the PE routers.
– PE routers provide the VPN routing and services via MP-BGP.
– P routers do not participate in VPN routing, and only provide core IGP backbone routing to the PE routers.
• The PE router functions are extended to carry regular Internet routing via IPv4 BGP in addition to the MP-BGP.
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-17
Summary (Cont.)
• PE routers separate the global IPv4 BGP routing table from each unique customer VPNv4 MP-BGP routing table.
• The ingress PE router receives CE customer IPv4 updates and exports these IPv4 routes to other PE routers via MP-BGP.
• The egress PE router imports the VPNv4 routes and forwards them to the CE router as an IPv4 update.
• Route distribution to destination CE routers is determined by BGP communities using route targets and an optional SOO for loop detection.
© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—4-18