basics of mpls
DESCRIPTION
Basics of MPLSTRANSCRIPT
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1© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics 1
Basics of MPLS
Cisco Advanced Services EDCS-336890
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222© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
• Introduction
Name, Location and Current profile
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333© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Agenda
• Business Drivers for MPLS
• MPLS Capabilities
• MPLS Concepts
• Basic MPLS Forwarding
• Basic MPLS Applications
Hierarchical Routing
IP+ATM Integration
• Summary and Benefits of MPLS
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Business Drivers for MPLS
444© 2003 Cisco Systems, Inc. All rights reserved.
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555© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Old World New World
Changing Telecom Landscape
Infrastructure
Traffic
Services Focus
Private Networks
Business Networks
OSS
In-House
FR-Based VPNs
Voice-Centric
Transport
Circuit-Switched
Network-Based Service-Based
Outsourced
IP Value-Added
IP-Based VPNs
Data-Centric
Packet-Switched
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666© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Customer Requirements
Businesses are building on IPBusinesses are building on IP Businesses need Businesses need privateprivate
IP servicesIP services
CustomersSuppliersPartners
TelecommutersMobile Users
RemoteOffices
IP Intranet IP Extranet
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777© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
ValueValue--AddedAdded
IP ServicesIP Services
Problem:How to Build a Network
that Can Deliver theseServices andand SLAs
Service Provider Requirements
Growth: IP ConnectionGrowth: IP Connection
Internet, Intranet, Internet, Intranet,
ExtranetExtranet
Multimedia
Content
Hosting
Service Portfolio
Revenue: TransportRevenue: Transport
Frame Relay, ATM, Frame Relay, ATM,
Managed ServicesManaged Services
ManagedIntranets
PrivateVoice Networks
Profit: IP VASProfit: IP VAS
Hosting, Voice, Hosting, Voice,
Video, ASPVideo, ASP’’ss
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888© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
The Barriers
• Carriers’ customers want IP services:
They need connectionless IP services
They need more flexible IP quality of service guarantees
They need more privacy than the Internet provides
• Frame Relay and ATM services are available:
They provide connection-oriented service
They have inflexible point-to-point bandwidth guarantees
But they have good privacy
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999© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
The Solution - MPLS
• MULTI-PROTOCOL LABEL SWITCHING
• A mechanism that delivers the best of both worlds:
PRIVACY and QOS of ATM, 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
scales to large and small private networks
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101010© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS Basics
• Traditional routing
Each router holds entire routing table and forwards to next hop (destination based routing)
• MPLS combines L3 routing with label swapping and forwarding
• MPLS Forwarding
Label imposed once at ingress routerAll forwarding decisions then made on label only – no routing table lookups
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MPLS Capabilities
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Key Cisco MPLS Capabilities
IP/ATM Integration Traffic Engineering
VPN’s
IP Multicast IP CoS
RSVP
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131313© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
• Put routers around the edge of an ATM network
• Connect routers using Permanent Virtual Circuits
• This does not provide optimal integration of IP and ATM
Traditional IP over ATM
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141414© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
IP+ATM Integration
• Internal routing scalability
Limited adjacencies
• External routing scalability
Full BGP4 support, with all the extras
• VC merge for very large networks
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151515© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Traffic Engineering
Route chosen byIP routing protocol
Route specified bytraffic engineering
• Why traffic engineer?
Optimise link utilisation
Specific paths by customer or class
Balance traffic load
• Traffic follows pre-specified path
• Path differs from normally routed path
• Controls packet flows across a L2 or L3 network
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161616© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS VPNs
• Private, connectionless IP VPNs
• Outstanding scalability
• Customer IP addressing freedom
• Multiple QoS classes
• Secure support for intranets and extranets
• Simplified VPN Provisioning
• Support over any access or backbone technology
VPN C
VPN A
VPN B
VPN C
VPN AVPN B
VPN C
VPN A
VPN B
VPN CVPN A
VPN B
Connection-Oriented VPN Topology
VPN C
VPN A
VPN B
VPN C
VPN AVPN B
VPN C
VPN A
VPN BVPN C
VPN AVPN BConnectionless
VPN Topology
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171717© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Single carrier networkSingle carrier network
supporting multiple supporting multiple
customer IP VPNscustomer IP VPNs
Separately engineeredSeparately engineeredcustomer private IP
networks
BGP+ MPLSNetwork
vs.
Build once,Sell once
Build once,Sell once
Build once,Sell many
Build once,Sell many
MPLS VPNs
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181818© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Core
Provider Edge
Edge
LSR
18© 1999, Cisco Systems, Inc. www.cisco.com0905_04F9_c1
TechnologiesCPE
Edge
LSR
• Provider Edge LSR
CAR (packet classification and rate limiting)
MPLS enabled
Precedence Mapping
• Core LSR
WRED (sets drop policy for congestion management)
WFQ/MDRR (queuing policies)
Fast MPLS switching
MPLS end to end class of service
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MPLS Concepts
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202020© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS concepts
• MPLS: Multi Protocol Label Switching
• Packet forwarding is done based on labels
• Labels are assigned when the packet enters into the network
• Labels allocated from a LOCAL POOL in the router
• Labels are on top of the packet
• MPLS nodes forward packets/cells based on the label value (not on the IP information)
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MPLS concepts
• MPLS allows:
Packet classification only where the packet enters the network
The packet classification is encoded as a label
In the core, packets are forwarded without having to re-classify them
No further packet analysis
Label swapping
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222222© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS Components
• Edge Label Switching Routers (ELSR)
label previously unlabeled packets - at the beginning of a Label Switched Path (LSP)
strip labels from labeled packets - at the end of a Label Switched Path
• Label Switching Routers (LSR)
forward labeled packets based on the information carried by labels
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232323© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS Components
LSR LSR
LSR LSR
ELSR
ELSR
P Network(Provider Control)
PECE CEPE
ELSR
ELSR
C Network(Customer Control)
C Network(Customer Control)
P
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Functional Components
• Forwarding component:
uses label information carried in a packet and label binding information maintained by a Label Switching Router to forward the packet
• Control component:
responsible for maintaining correct label binding information among Label Switching Routers
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252525© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Forwarding Component
• Label Forwarding Information Base (LFIB)
each entry consists of:
incoming labeloutgoing labeloutgoing interfaceoutgoing MAC address
LFIB is indexed by incoming label
LFIB could be either per Label Switching Router, or per interface
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Forwarding Component
• IOS Label Forwarding Code is based on Cisco Express Forwarding (CEF)
Maintenance of label rewrite structures in LFIB
Recursive route resolution
IP to label switching (label imposition) path
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Forwarding Component
• Forwarding algorithm:
Extract label from a packet
Find an entry in the LFIB with the INCOMING LABEL equal to the label in the packet
Replace the label in the packet with the OUTGOING LABEL(from the found entry)
Send the packet on the outgoing interface (from the found entry)
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Forwarding Component
• Carrying label information:
as part of the MAC header:
- VCI/VPI in ATM
via a “shim” between the MAC and the Network Layer header
• Label information can be carried over any Link Layer
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292929© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Label Header (Shim)
Label
1 2 3 4 5 6 7 8
EXP S
TTL
Bit
2
3
4
1
Byte
LabelEXP
STTL
Label Value (20 bits)Class of Service (3 bits)
Bottom of Stack (1 bit)Time to Live
•Can be used over Ethernet, 802.3, or PPP links•Require 2 new Ethertypes/PPP PIDs•One for unicast, one for multicast
•Four octets per label in stack
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303030© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
PPP
Ethernet
Frame Relay
Label IP header
Label
Label
IP Header
IP Header Data
ATM Header Label
IP Header
Data
ATM Header
Packet over SONET/SDH
Ethernet
Frame Relay PVC
ATM PVC’s
Subsequent cells
Data
Data
Data
GFC DataVPI VCI PTI CLP HEC
IP Header
GFC DataVPI PTI CLP HECVCI
Label
Label
Subsequent cells
ATM label switching
FR
AME
CE
LL
Label Encapsulation
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313131© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Control Component
• Labels can be distributed by several protocols
TDP/LDP – from IGP routes
RSVP – for traffic engineering paths
BGP – for VPN routes
• Responsible for binding between labels and routes:
Create label binding (local)
Distributing label binding information among Label Switching Routers
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MPLS Forwarding Decisions
• Packets are forwarded based on the label value
• IP header and forwarding decision have been de-coupled for better flexibility
• Other paradigms may be used to forward traffic
• No need to strictly follow unicast destination based routing
• Allows to have distinct forwarding decision based on different control component
Destination unicast routing, Traffic Engineering
Multicast, VPN, QoS
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Basic MPLS Forwarding
333333© 2003 Cisco Systems, Inc. All rights reserved.
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343434© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS: Forwarding
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MPLS: Forwarding
Existing routing protocols (e.g. OSPF, IGRP) establish routes
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MPLS: Forwarding
Label Distribution Protocol (e.g., LDP) establishes label to routes mappings
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373737© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS: Forwarding
Label Distribution Protocol (e.g., LDP) creates LFIB entries on LSRs
IN OUT I/F MAC
POP 32 E0/0 aa-00-bb
POP 27 E0/1 aa-00-cc
IN OUT I/F MAC
16 32 S0/0 aa-00-bb
18 27 S0/1 aa-00-cc
IN OUT I/F MAC
16 32 S0/0 aa-00-bb
18 27 S0/1 aa-00-cc IN OUT I/F MAC
16 POP S0/0 aa-00-bb
18 POP S0/1 aa-00-cc
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383838© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS: Forwarding
IN OUT I/F MAC
POP 32 E0/0 aa-00-bb
POP 27 E0/1 aa-00-cc
IN OUT I/F MAC
16 32 S0/0 aa-00-bb
18 27 S0/1 aa-00-cc
IN OUT I/F MAC
16 32 S0/0 aa-00-bb
18 27 S0/1 aa-00-cc IN OUT I/F MAC
16 POP S0/0 aa-00-bb
18 POP S0/1 aa-00-cc
Ingress edge LSR receives packet, performs Layer 3 value-added services, and “label” packets
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393939© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS: Forwarding
IN OUT I/F MAC
POP 32 E0/0 aa-00-bb
POP 27 E0/1 aa-00-cc
IN OUT I/F MAC
16 32 S0/0 aa-00-bb
18 27 S0/1 aa-00-cc
IN OUT I/F MAC
16 32 S0/0 aa-00-bb
18 27 S0/1 aa-00-cc IN OUT I/F MAC
16 POP S0/0 aa-00-bb
18 POP S0/1 aa-00-cc
LSRs forward labelled packets using label swapping
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404040© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS: Forwarding
IN OUT I/F MAC
POP 32 E0/0 aa-00-bb
POP 27 E0/1 aa-00-cc
IN OUT I/F MAC
16 32 S0/0 aa-00-bb
18 27 S0/1 aa-00-cc
IN OUT I/F MAC
16 32 S0/0 aa-00-bb
18 27 S0/1 aa-00-cc IN OUT I/F MAC
16 POP S0/0 aa-00-bb
18 POP S0/1 aa-00-cc
Edge LSR at egress removes remaining label* and delivers packet
* Pentulimate hop popping actually occurs. There may may not necessarily be a label in the packet at the ultimate or egress LSR.
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414141© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Traditional RoutingRoute Distribution
0
0
Routing Updates (OSPF, EIGRP…)
You Can Reach 128.89and 171.69 thru me
You Can Reach 128.89 thru Me
You Can Reach 171.69 thru Me
11171.69171.69
…………
11128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
1
22171.69171.69
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
128.89
171.69
1
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
2
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424242© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
11171.69171.69
…………
11128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
22171.69171.69
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
Traditional RoutingPacket Routing
2
0
0
1
128.89
Packets Forwarded
Based on IP Address
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
1
171.69
Data | 128.89.25.4
Data | 128.89.25.4
Data | 128.89.25.4 Data | 128.89.25.4
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434343© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
InInLabelLabel
OutLabel
11171.69171.69
…………
11128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
MPLS ForwardingIn/Out Label Fields
2
0
0
1
128.891
InInLabelLabel
OutLabel
22171.69171.69
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
171.69
InInLabelLabel
OutLabel
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
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444444© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
171.69
3636
3131
InInLabelLabel
2929
2727
OutLabel
11171.69171.69
…………
11128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
Frame Based MPLSAssigning Labels
2
0
0
1
128.891
2929
2727
InInLabelLabel
2222
PopPop
OutLabel
22171.69171.69
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
Pop Label for 128.89
Use Label 22 for 171.69
Use Label 27 for 128.89
Use Label 29 for 171.69
Unsolicited Downstream
Label Allocation
PopPop
InInLabelLabel
--
OutLabel
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
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454545© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
171.69
3636
3131
InInLabelLabel
2929
2727
OutLabel
11171.69171.69
…………
11128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
Frame Based MPLSPacket Forwarding
2
0
0
1
128.891
2929
2727
InInLabelLabel
2222
PopPop
OutLabel
22171.69171.69
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
128.89.25.4Data
Data 171.69.21.7 29Penultimate Hop
(Pop the label)
Data 128.89.25.4 27
128.89.25.4Data
171.69.21.7Data Data 171.69.21.7 22
PopPop
InInLabelLabel
--
OutLabel
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
128.89.25.4Data
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Basic Application – Hierarchical Routing
464646© 2003 Cisco Systems, Inc. All rights reserved.
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Hierarchical Routing
Border Routers Run BGP with External Peers
InteriorRouters
All Routers Run IBGP to Learn Exterior Routing Information, and IGP for Interior Topology
Conventional Approach
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Hierarchy of Routing Knowledge
• Isolate inter-domain and intra-domain routing
Improved stability
• Reduce interior router table size
Only IGP routes stored at interior nodes
• Improve BGP scaling
Only border nodes need run BGP
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494949© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Internet Scalability
2
01
128.89136.50156.50
119.10
1
171.69127.18204.162
PopPop
InInLabelLabel
--
OutLabel
…………
--150.10.1.1150.10.1.1
OutOutI/FI/F
AddressAddressPrefixPrefix
EBGP
EBGP
Loopback 150.10.1.1
Loopback 150.10.1.2
1717
1616
InInLabelLabel
2222
PopPop
OutLabel
22150.10.1.2150.10.1.2
…………
00150.10.1.1150.10.1.1
OutOutI/FI/F
AddressAddressPrefixPrefix
--
InInLabelLabel
1717
1616
OutLabel
11150.10.1.2150.10.1.2
…………
11150.10.1.1150.10.1.1
OutOutI/FI/F
AddressAddressPrefixPrefix
I can reach…
128.89,136.50156.50,119.10
via the BGP next hop
150.10.1.1 using onlylabel 16!
0
![Page 50: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/50.jpg)
Basic Application – IP+ATM
505050© 2003 Cisco Systems, Inc. All rights reserved.
![Page 51: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/51.jpg)
515151© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS and ATM
• Label Switching Steps:
Make forwarding decision using fixed-length Label
Rewrite label with new value
Similar to ATM cell switching
• Key differences:
Label set up: LDP vs ATM Forum Signaling
Label granularity: Per-prefix
![Page 52: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/52.jpg)
525252© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS and ATM
• Common forwarding paradigm
label swapping = ATM switching
• Use ATM user plane
use VPI/VCI for labels
Label is applied to each cell, not whole packet
• Replace ATM Forum control plane with the MPLS control component:
Network Layer routing protocols (e.g., OSPF, BGP, PIM) + Label Distribution Protocol (e.g., LDP)
![Page 53: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/53.jpg)
535353© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Label Distribution for ATM
• Uses LDP in “Downstream on Demand” mode
• Referred to as Cell Based MPLS (rather than Frame Based MPLS)
• Label Virtual Circuit (LVC) labels are requested when topology changes
• Precedence can be associated with Label Virtual Circuit (LVC)
• Some LDP extensions for negotiation of ATM specific parameters
![Page 54: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/54.jpg)
545454© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
171.69
--
--
InInLabelLabel
3030
2727
OutLabel
11171.69171.69
…………
11128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
Cell Based MPLSAssigning Labels
2
0
0
1
128.891
3030
2929
2727
InInLabelLabel
1616
1919
1818
OutLabel
00128.89128.89
22171.69171.69
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
1919
1818
InInLabelLabel
--
--
OutLabel
00128.89128.89
…………
00128.89128.89
OutOutI/FI/F
AddressAddressPrefixPrefix
DownstreamOn demand
Label Allocation
Need a Label for 128.89
Need a Label for 171.69
Need a Label for 171.69
Need a Label for 128.89
Need a Label for 128.89
Need a Label for 128.89
![Page 55: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/55.jpg)
555555© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Cells
1
Labels act as the VCidentifier for ATM
Switches (Label VC or LVC)
Labels change betweenswitches - LVCs arenot end-to-end.
Cell Based ATM MPLSForwarding Cells
In Label
In Label
11
……
Address Prefix
Address Prefix
128.89128.89
……
OutI/F
OutI/F
00
……
Out Label
Out Label
33
……
In I/F
In I/F
55
……
ELSR LSR
GFC DataVPI PTI CLP HECVCI
Label
33 33 33 33
55 55 55 55
PacketPacket 128.890
1
![Page 56: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/56.jpg)
565656© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
128.89
In Label
In Label
55
88
……
Address Prefix
Address Prefix
128.89128.89
128.89128.89
……
OutI/F
OutI/F
00
00
……
Out Label
Out Label
33
33
……
In I/F
In I/F
11
22
……
2
Cell Based ATM MPLSMultiple Labels (1)
• If multiple labels were not allocated
Cells of different packets would have same label (VPI/VCI)
Egress router can’t reassemble packets
3333
88
5555
5555
8888
88 3333 3333
PacketPacket
PacketPacket
Cells
Help!Help!1
0
![Page 57: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/57.jpg)
575757© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
128.89
Cell Based ATM MPLSMultiple Labels (2)
• Multiple labels enable edge router to reassemble packets correctly
In Label
In Label
55
88
……
Address Prefix
Address Prefix
128.89128.89
128.89128.89
……
OutI/F
OutI/F
00
00
……
Out Label
Out Label
33
77
……
In I/F
In I/F
11
22
……
2 3377
88
5555
5555
8888
88 3377 3377
PacketPacket
PacketPacket
Cells
10
Cool!Cool!
![Page 58: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/58.jpg)
585858© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
128.89
VC Merge
• With ATM switch that can merge VCs
Can reuse outgoing label
Hardware prevents cell interleave
Fewer labels required
For very large networks
In Label
In Label
55
88
……
Address Prefix
Address Prefix
128.89128.89
128.89128.89
……
OutI/F
OutI/F
00
00
……
Out Label
Out Label
33
33
……
In I/F
In I/F
11
22
……
2 3333
88
5555
5555
8888
88 3333 3333
PacketPacket
PacketPacket
Cells
10
![Page 59: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/59.jpg)
595959© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
VC Merge
Without VC Merge With VC Merge
• VC Merge is used to merge Label VCs (LVCs) going to the same destination
• VC Merge greatly improves IP-over-ATM scalability
![Page 60: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/60.jpg)
606060© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS Stack
IP RoutingIP Routing
MPLS SignallingMPLS Signalling
Labels on Layer 2Labels on Layer 2
MPLS: Another View
• The MPLS protocol stack consists of IP Routing and MPLS signalling, together setting up connectivity at layer 2
• Much of the complexity in the MPLS stack is in IP Routing
![Page 61: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/61.jpg)
616161© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS and ATM Services
• ATM services for real-time services
P-NNI / UNI Signaling
Voice trunking
Circuit Emulation (CES)
• MPLS for data traffic
Offloads signaling-intensive traffic
Reduces call set-up dependencies
CoCo--Existing on Same PlatformExisting on Same Platform
ATM
IPFR
ATM
FR
IP IP
![Page 62: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/62.jpg)
626262© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
MPLS is an ATM Control Stack
• MPLS and ATM Forum protocols can co-exist on same the same links and switches
• ATM MPLS sets up Label VCs (LVCs) according to IP Routing information
• Label VCs (LVCs) are not PVCs or SVCs
• LVCs, SVCs and PVCs can coexist on same links in different VPIs
IP RoutingIP Routing
MPLS SignallingMPLS Signalling
L2 VCsL2 VCs
PNNI RoutingPNNI Routing
UNI/NNI SignallingUNI/NNI Signalling
MPLS
Stack
ATM Forum
Stack
![Page 63: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/63.jpg)
Summary and Benefits
636363© 2003 Cisco Systems, Inc. All rights reserved.
![Page 64: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/64.jpg)
646464© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Summary
• MPLS allows flexible packet classification and network resources optimisation
• Labels are distributed by different protocols
LDP, RSVP, BGP
• Different distribution protocols may co-exist in the same LSR
• Labels have local (LSR) significance
No need for global (domain) wide label allocation/numbering
![Page 65: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/65.jpg)
656565© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Advanced MPLS
• Basic MPLS: destination-based unicast
• Many additional options for assigning Labels
• The Key: separation of routing and forwarding
Destination-Based Unicast Routing
IP Classof Service
Resource
Reservation(Eg. RSVP)
Multicast
Routing (PIM v2)
Explicit and
Static Routes
Virtual
Private Networks
Label Information Base (LIB)
Per-Label Forwarding, Queuing,
and Multicast Mechanisms
![Page 66: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/66.jpg)
666666© 2003 Cisco Systems, Inc. All rights reserved.MPLS Training - Basics
Benefits of MPLS
• De-couples IP packet forwarding from the information carried in the IP header of the packet
• Provides multiple routing paradigms (e.g., destination-based, explicit routing, VPN, multicast, CoS, etc…) over a common forwarding algorithm (label swapping)
• Facilitates integration of ATM and IP - from control plane point of view an MPLS-capable ATM switch looks like a router
![Page 67: Basics of MPLS](https://reader031.vdocuments.net/reader031/viewer/2022013004/577cc5011a28aba7119af7e6/html5/thumbnails/67.jpg)
676767