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2001, Cisco Systems, Inc. Chapter2-1
Chapter 2
MPLS Overview
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Objectives
Upon completion of this chapter, you willbe able to:
Place MPLS technology within the network. Provide a high-level description of MPLS
technology.
Identify services provided by MPLS
technology.
Explain the features and benefits of MPLStechnology.
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2001, Cisco Systems, Inc. Chapter2-3
Driving Business Forces
from Old World to New
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Business Perspective
Businesses are building on IPBusinesses need private
IP services
CustomersSuppliersPartners
Telecommuters
Mobile Users
RemoteOffices
IP Intranet IP Extranet
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Virtual Private Networking:A $24 Billion Opportunity
35%
6%
5%
54%
ATM/FR Managed Svcs
IP VPNs Unrealized
1998 VPN Service Distribution
0
5
10
15
20
25
1998 2001 2004
ATM/FR Managed Svcs IP VPNs Total
Worldwide VPN Service Revenues
(Billions of Dollars)
Source: CIMI Corp.
Barriers?IP+ATM Opportunity
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New World Requirements
Transport Services Leased line, Frame Relay, ATM
(current business processes)
Revenue
IP Connectivity Services Internet Intranet Extranet
Growth
IP Valued-Added Services Content hosting Collaboration Voice Video
Profit
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IP/VPN SLA
requirementscannot be met with
todays
technology!
Customer Perspective
Current Requirements
QoS
Privacy
Availability
Reliability
New Requirements
Multiple service classes
Multiple service options
ATM, Frame Relay,Private IP, Public IP
Multiple VPN options
Lower-cost managedservices
Any-to-any connectivity
Extranets, COINS(Community of InterestNetworks)
Seamless integration
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The Problem
We cant get there from here using traditionaltechnologies:
ATM or Frame Relay virtual circuits
IP tunneling Encryption
Network address translation
Why?
Functionality trade-offs
Complexity
Cost
Service degradation
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The Solution: MPLS
A new paradigm that delivers the best of bothworlds:
Privacy and QoS of ATM and Frame Relay
Flexibility and scalability of IP
Foundation for IP business services:
Flexible grouping of users and value-added
services Low-cost managed IP services:
Scalabilitysmall to large private networks
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MPLS: New Industry Standardfor Carrier Networks
What is it? Multiprotocol Label Switching
Emerging IETF industry standard
Based on Ciscos tag switching
How does it work? Forwards packets based on labels
Packets are switched, not routed
Labels represent destination and service attributes
(CoS, PrivacyVPNs, traffic engineering) Multiple mechanisms for assigning and distribution labels
(Tag Distribution Protocol, Label Distribution Protocol,Resource Reservation Protocol, Border Gateway ProtocolVersion 4)
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MPLS: The First CompleteIP Solution
Any-to-Any Connectivity
Leased Lines
Frame Relay/ATM
IP
MPLS
UserN2
N2(logical)
N
N
NetworkN2
N2(logical)
N
N
QoS
Privacy
Low-CostManagedServices
MPLS is the firstsolution that delivers on all the requirementsfor New World private IP networks.
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MPLS Technology
Overview
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Why MPLS in the Internet?
Integrate best of Layer 2and Layer 3
Keep up with growth
Reduce operations costs
Increase reliability
Create foundation for newrevenue from advanced IPservices
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MPLS Routing Scalability
Internal routingscalability
Limited adjacencies
External routingscalability
Full BGP4 support, with
extensionsVC merge for very largenetworks
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MPLS: End-to-End IPServices over ATM
IP services mappeddirectly onto ATMswitches
MPLS label tocell stream
Avoids complextranslation
Full support for IP QoS,VPN, and TrafficEngineering
IPMulticast IPCoS
RSVP
IP Multicast
IP Multicast
IP CoS
RSVP
IP
Multicast
R12
R45
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MPLS and ATM ServicesCoexisting on Same Platform
ATM standard services Private Network-
Network Interface /User-Network
Interface Signaling Voice trunking
Circuit emulation
MPLS Services
VPN CoS Traffic engineering
FR
IPATM
ATM MPLS
MPLS
IPFR
IP
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MPLS Across Non-MPLSATM Networks
ATM Network
MPLS Network
Labeled cellsaretransported ina virtual path
ATM VCsare createdas needed;
virtualchannelidentifiersare mappedto labels.
LSRLabelSwitchRouter
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Benefits of MPLSCoS with ATM
IP QoS over Standard ATM
Allocate resources:
Per-individual, edge-to-edge VCs
By kbps bandwidth Mesh of VCs to configure
Complex error recovery
Wasted/inaccessible bandwidth
CoS with MPLS
Allocate resources:
Per-class, per-link
By % bandwidth No VCs to configure
No wasted bandwidth
Contained error recovery
Simpler to provision and
engineer
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A New Paradigm for VPNs
VPN A
VPN B
VPN C
VPN A VPN BVPN C
VPN A
VPN BVPN C
VPN A
VPN C
VPN B
MPLS-Based VPNs
Network privacy
Network-based (subnets)
IP and VPN-aware
groups users and services
Overlay VPN
Frame Relay/VC privacy
VC-based
Frame Relay/ATM aware
groups endpoints
extranet
intranet
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MPLS-Based VPN Benefits
Frame Relay privacy In a connectionless IP network Without tunnels or encryption
VPN-aware networks
Flexible user and servicegrouping
Multiple COS service classes
Scales to large and small VPNs
Low-cost managed services
No inherent scalability limits
Secure Intranets and Extranets
Multiple customer
memberships Provides Internet access
Simplified managed networks
No new PVCs to provision
No traffic matrix to update
No PVC mesh to resize
No routing topology to update
Simpler for the customer
No new application paradigms
No translation required forprivate IP addresses
No special CPE requirements
Simplified routing
Support over any access orbackbone technology
Standards based
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A New Paradigm forManaged Networks
Single-carrier networksupporting multiplecustomer IP VPNs
Separately engineeredcustomer private IPnetworks
MPLSNetwork
Vs.
Build once,sell many
Build once,
sell once
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Overlay VPN MPLS-Based VPN
LSRCPE
Lower Operational Cost
Update traffic matrix
Add (N 1) PVCs for new CPE
Resize full PVC mesh
Update OSPF design
Reconfigure each CPE for new Layer 3topology
Configure new CPEUpdate Edge LSR
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Leveraging Todays IP QoSSolutions
Technology Function
IP precedence Prioritization (in IP header) Indicates service class
Committed Access Rate (CAR) Packet classification byapplication, protocol, etc.
Sets precedence Bandwidth management: discard
or change service class
WRED Weighted Random Early Detection Congestion avoidance Service-class enforcement
WFQ, CBQ Weighted Fair Queuing Class-based Queuing Queuing policies (e.g. latency)
MPLS IP +ATM CoS Integration Traffic Engineering
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MPLS Class of Service
CoS
Distinct service classes implemented by network
Traffic flows classified
Based on Layer 3
Simpler and more efficient than mesh VCs
Two methods to indicate service class:
IP precedence copied to MPLS header (CoS field)
Up to 8 classes can be defined (3 bits)
Separate labels used for different service classes
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Benefits of MPLS CoS
IP CoS over ATM/FrameRelay VPNs
Allocate resources:
Per-individual,edge-to-edge VCs
By kbps bandwidth
Mesh of VCs to configure
Wasted/inaccessible bandwidth
IP CoS with MPLS VPNs
Allocate resources efficiently:
Per-class, per-link by % of
bandwidth Maximize transport of paid traffic
No connections to configure
Flexibility without added overhead
No wasted bandwidth as with PVCs
No call setup overhead aswith SVCs
Add traffic engineering
Path route consistency per flow
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Motivations for TrafficEngineering
Economics
Failure scenarios
Unanticipated traffic
300 MbpsTraffic Flow
155 Mbps Fiber Link
Link Failure
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MPLS Operation
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MPLS Terminology
Label Switch Router (LSR)= Router= ATM Switch + LSC
Label DistributionProtocol (LDP)
ATM EdgeLSR
Edge functions
Core Functions
Label Edge Router= LER
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Label Switched Path
Label DistributionProtocol (LDP)
ATM EdgeLSR
Edge Functions
Core FunctionsLSP
PE1
PE10
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MPLS Labels
Basic MPLS: destination-based unicast
Labels divorce forwarding from IP address
Many additional options for assigning labels
Labels define destination and service
The key: separation of routing and forwarding
Destination-
basedUnicastRouting
IP
CoS
Resource
Reservation(RSVP)
Multicast
Routing(PIM v2)
Explicit &
StaticRoutes
VPNs
Label Information Base (LIB)
Per-Label Forwarding, Queueing and Multicast Mechanisms
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MPLS Operation
CECE
PE
PE
1. Existing routing protocols (e.g., OSPF, IS-IS, BGP)establish reachability to destination networks.
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1. Existing routing protocols (e.g., OSPF, IS-IS)establish reachability to destination networks.
MPLS Operation (cont.)
2. Label Distribution Protocol (LDP)establishes label-to-destinationnetwork mappings.
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1. Existing routing protocols (e.g., OSPF, IS-IS)establish reachability to destination networks.
2. Label Distribution Protocol (LDP)establishes label-to-destinationnetwork mappings.
MPLS Operation (cont.)
3. Ingress Edge LSR receivespacket, performs Layer 3 value-added services, and labels
packets.
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1. Existing routing protocols (e.g., OSPF, IS-IS)establish reachability to destination networks.
2. Label Distribution Protocol (LDP)establishes label-to-destinationnetwork mappings.
3. Ingress Edge LSRreceives packet, performsLayer 3 value-added services,
and labels packets.
4. LSR switchespackets using labelswapping.
MPLS Operation (cont.)
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1. Existing routing protocols (e.g., OSPF, IS-IS)establish reachability to destination networks.
2. Label Distribution Protocol (LDP)establishes label-to-destinationnetwork mappings.
3. Ingress Edge LSRreceives packet, performsLayer 3 value-added services,
and labels packets.
MPLS Operation (cont.)
4. LSR switches packets
using label swapping.
5. Egress LSR removes labeland forwards standard IP
packet to customer.
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Router Example: DistributingRouting Information
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Router Example: ForwardingPackets
Packets are forwarded on the
basis of IP address.
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MPLS Example: RoutingInformation
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MPLS Example: AssigningLabels
S
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MPLS Example: ForwardingPackets
LER LERLSR
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MPLS Example: Shared Labels
Prefixes that share apath can share a label.
MPLS E l
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MPLS Example:Label Disposition
MPLS NetworkEgress LER
CERouter
RemovesLabel
MPLS E l
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MPLS Example:Standard IP mode
MPLS NetworkEgress LER
Deaggregation Pointdoes Layer 3 Lookup
CERouter
L b l H d
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Label HeaderPacket Media
Can be used over Ethernet, 802.3, or PPP links
Contains everything needed at forwarding time
One word per label
Label = 20 bitsExperimental = Class of Service, 3 bitsS = Bottom of Stack, 1 bit
TTL = Time to Live, 8 bits
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MLSTE 1.0Chapter2-45 2001, Cisco Systems, Inc.
Encapsulations
ATM Cell Header
PPP Header(Packet overSONET/Synchronous
Digital Hierarchy)
LAN MACLabel Header
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MPLS A N MPLS
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MPLS Across Non-MPLSATM Networks
Labeled cellsare transportedin a virtualpath.
ATM Network
MPLS Network
ATM VCs
are createdas needed;VCIs aremapped tolabels.
LSRLabelSwitchRouter
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MLSTE 1.0Chapter2-48 2001, Cisco Systems, Inc.
Summary
MPLS is the enabling technology to supportNew World services.
Significant customer demand for IP+ATMcapabilities.
Build oncesell many.
MPLS combines the best features of Layer 2(ATM) and Layer 3 (IP).
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MLSTE 1.0Chapter2-49 2001, Cisco Systems, Inc.
Review Questions (cont.)
1. Why do current (traditional) technologies
prove inadequate to deliver New WorldServices?
2. How do MPLS-forwarded packets carrydestination and service attributes such as
CoS, VPN, and Traffic Engineering?3. What MPLS mechanism allows IP services to
be mapped easily onto ATM switches?
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Review Questions (cont.)
4. What type of device is responsible for
adding or removing MPLS labels?5. Which field in the label is used to
map the IP precedence bits?
6. What technique is used to translate thepacket-based label for an ATMnetwork?