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© 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
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