© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-1 MPLS Concepts Introducing Basic MPLS Concepts © 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-2 Outline • Overview • What Are the Foundations of Traditional IP Routing? • Basic MPLS Features • Benefits of MPLS • What Are the MPLS Architecture Components? • What Are LSRs? • Summary © 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-3 Foundations of Traditional IP Routing • Routing protocols are used to distribute Layer 3 routing information. • Forwarding decision is made based on: – Packet header – Local routing table • Routing lookups are independently performed at every hop. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-4 Traditional IP Routing • Every router may need full Internet routing information. • Destination-based routing lookup is needed on every hop. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-5 Basic MPLS Features • MPLS leverages both IP routing and CEF switching. • MPLS is a forwarding mechanism in which packets are forwarded based on labels. • MPLS was designed to support multiple Layer 3 protocols • Typically, MPLS labels correspond to destination networks (equivalent to traditional IP forwarding). © 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-6 MPLS Architecture: Control Plane © 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-7 MPLS Architecture: Data Plane © 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-8 MPLS Devices: LSRs • The LSR forwards labeled packets in the MPLS domain. • The edge LSR forwards labeled packets in the MPLS domain, and it forwards IP packets into and out of the MPLS domain. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-9 Label Switch Routers: Architecture of LSRs © 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-10 LSR Architecture Example MPLS router functionality is divided into two major parts: the control plane and the data plane. [...]... Architecture of Edge LSRs © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-11 Basic MPLS Example • MPLS core routers swap labels and forward packets based on simple label lookups • MPLS edge routers also perform a routing table lookup, and add or remove labels © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-12 MPLS Labels • Are 4 byte identifiers used for forwarding decisions • Define... reserved MPLS v2.2—1-13 MPLS Labels: Frame-Mode MPLS © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-14 MPLS Label Operations: Frame Mode • • • On ingress, a label is assigned and imposed LSRs in the core swap labels based on the contents of the label forwarding table On egress, the label is removed and a routing lookup is used to forward the packet © 2006 Cisco Systems, Inc All rights reserved MPLS. .. Cisco Systems, Inc All rights reserved MPLS v2.2—1-15 MPLS Unicast IP Routing Architecture (Cont.) © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-16 MPLS Unicast IP Routing Architecture (Cont.) © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-17 MPLS Unicast IP Routing Architecture (Cont.) © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-18 LSP Building The IP routing protocol... received from the next-hop LSR © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-28 Packet Propagation Across an MPLS Network © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-29 Extranet VPNs: Peer-to-Peer VPN Implementation © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-30 MPLS VPN Architecture An MPLS VPN combines the best features of an overlay VPN and a peer-to-peer VPN:... Systems, Inc All rights reserved MPLS v2.2—1-31 MPLS VPN Architecture: Terminology Note: • • © 2006 Cisco Systems, Inc All rights reserved PE Router = Edge LSR P Router = LSR MPLS v2.2—1-32 PE Router Architecture • PE router in an MPLS VPN uses virtual routing tables to implement the functionality of customer dedicated PE routers © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-33 Propagation of... 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-19 LSP Building (Cont.) LDP propagates labels to convert the path to an LSP © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-20 PHP: Before • Double lookup is not an optimal way of forwarding labeled packets • A label can be removed one hop earlier © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-21 PHP: After A label is removed... removed on the router before the last hop within an MPLS domain © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-22 Label Distribution and Advertisement The allocated label is advertised to all neighbor LSRs, regardless of whether the neighbors are upstream or downstream LSRs for the destination © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-23 Label Distribution and Advertisement:... also store the label information in the FIB © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-24 Label Distribution and Advertisement: Interim Packet Propagation Forwarded IP packets are labeled only on the path segments where the labels have already been assigned © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-25 Label Distribution and Advertisement: Further Label Allocation Every LSR... every destination © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-26 Label Distribution and Advertisement: Receiving Label Advertisement • Every LSR stores received information in its LIB • LSRs that receive their label from their next-hop LSR will also populate the IP forwarding table © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-27 Populating the LFIB • Router B has already assigned... rights reserved MPLS v2.2—1-34 Propagation of Routing Information Across the P-Network (Cont.) Question: How will PE routers exchange customer routing information? Option #2: Run a single routing protocol that will carry all customer routes inside the provider backbone Better answer, but still not good enough: • P routers carry all customer routes © 2006 Cisco Systems, Inc All rights reserved MPLS v2.2—1-35 . All rights reserved. MPLS v2.2—1-1 MPLS Concepts Introducing Basic MPLS Concepts © 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—1-2 Outline. Systems, Inc. All rights reserved. MPLS v2.2—1-5 Basic MPLS Features • MPLS leverages both IP routing and CEF switching. • MPLS is a forwarding mechanism