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© M. Baldi: see page 2MPLS - 1

MPLSMulti-protocol label switching

Mario BaldiPolitecnico di Torino

(Technical University of Torino)

http://staff.polito.it/mario.baldi

© M. Baldi: see page 2MPLS - 2

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© M. Baldi: see page 2MPLS - 3

MPLS is the enabling technology for the New Broadband (IP) Public

Network

From MPLS Forum Documents

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IP

ATM

IP

Leased Line

Frame Relay

ATM CircuitEmulation

IP over DWDM

IP over ATM Circuit Emulation

IP over ATM

IP over SONET/SDH

IP over Frame Relay

WDM

IP

ATM

The “onion” that makes telecos “cry”

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IPIP router

with LAN or WAN

interface

IP router with T3 interfacePABX with T1 interfaceIP router with LAN (GE) or WAN (PoS) Interface

IP/MPLS

λ Switching

The future: WDM, IP, MPLS

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The idea

Instead of the IPdestination address

Forwarding packets according to a label

Label IP packet

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Why?

The label may be used as an index

Faster lookup

Traffic engineering

Instead of longest prefix matching

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MPLS introduces a connection-oriented

paradigm in IP networks

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Network architecture

Label edge routerIngress/egress LSR

Label switch router (LSR)

MPLS networkMPLS cloud

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Egress LSR

Ingress LSR

Label Switched Path (LSP)

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Label switching

D

D

1234

03

0

12

3

01

0

2

A

D

X

0

0

1

1

In Out

2

2

1

In Out

0

1

In Out

0

1In Out

0

1122

0

D

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MPLS history

Tag Switching

IP on ATM

No problems with resolution of addresses

Simpler signaling

Only one control plan

ATM with IP

Reusing ATM switching hardware

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MPLS history

MPλS (Multi-Protocol Lambda Switching)

G-MPLS (Generalized MPLS)

Packet switching

Cell switching

Circuit switching (SONET/SDH)

Lambda switching

Anything switching

Unifying control plan

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MPLS “header”

Contains the label

MPLS key elements

Upgraded routing protocols

Constraints in choosing paths

Protocols for label distribution

Signaling

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Shim headerMPLS header

Level 2 IP packet

Label Exp S TTL20 bit 3 bit 8 bit1

TTL: Time to live

Exp: Experimental bits (CoS)S: Bottom of stack

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VCI/VPI (ATM)

MPLS labels in layer 2 header

Connection oriented layer 2protocols

ATM and frame relay

DLCI (Frame relay)

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Forwarding equivalence class (FEC)

Packets that

Follow the same pathin MPLS network

Are treated the same wayby each LSR

Receive the same label

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Label Binding

A LSR determines the label it intends to use for packets belonging to a given FEC

Downstream binding

Packets of the FEC shall be received with chosen label

Upstream node to be notified

Unsolicited

On-demand

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Input label

Output port

LSP Creation

Label Mapping

The label used by the downstream switch of a link for packets

belonging to a FEC is associated to

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Downstream Label Binding

Label Distribution

The downstream switch of a link choses the label to be attached to packets belonging to a FEC when

forwarded on the link

The label is communicated to the upstream switch

Label mapping for the corresponding port

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Static label binding (and mapping)

Through management

Non-scalable

Equivalent to PVC ATM

No interoperability among managing systems

Impossible to have LSPs through different networks

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Dynamic label binding

Protocol (IP) driven

Explicit creation of LSP

The creation of LSPs is linked to the discovery of routes towards destinations

Explicit signaling

Initiated by label edge routers

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Routing protocol: BGP

Only protocol driven

Designed for allocation in integrated service networks

Resource reservation protocol (RSVP)

Label distribution protocols

Three alternatives (incompatible)

Label distribution protocol (LDP)

Designed for the purpose

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Routing protocols

Used to determine LSP routing

Guide label binding procedures

They indirectly determine packet routing

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carry topology information

Routing protocols

Existing protocols

IS-IS

OSPF

BGP-4

In MPLS context

they are enhanced d to...

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Routing protocols

...carry information to constraint routing decisions (constraint data)

Capacity of links

Link utilization

Dependencies among links

Used for fault recovery

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Enhanced routing protocols

Constraint based routingis fundamental to support

traffic engineering

IS-IS–TE

OSPF–TE

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Similar to routing for IP packets

Ingress and egress labels

Switches agree on corrispondencies among

Each switch decides the next stepof LSP path

Hop-by-hop routing

Labels and FEC

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The choice is constraint based

Constraint based routing

Explicit constraint based routing

For example, LSR ingress

A single switch may choose the path of an LSP

Explicit routing

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CR-LDP

Constraint-based routing LDP

Should be modified

Label distribution protocols

RSVP-TE

RSVP for Traffic Engineering

To be used withOSPF-TE and IS-IS-TE

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New possibilities

Traffic engineering

Per-class traffic engineering

Guaranteed quality of service

Fast fault recovery

Not yet supported

In less than 50 ms

Synergy with DiffServ

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Control plane and data plane

Data plane

Control plane

RIP IGRP

OSPF

BGPIS-IS

Routing database

Routingtable

Continuous updating

IP

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Control plane and data plane

Dataplane

Control plane

RIPIGRP

OSPF

BGP

IS-IS

Routing database

Forwarding table

MPLS

LDPRSVP

LSP setup

Signaling (LSP setup)

Routingtable

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Traditional IP routingTraffic for D on optimal path

D

Aggregation!

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Traditional IP routing

D

Traffic for D on optimal path4 overloaded linksCongestion!

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Traditional IP routingTraffic for D on optimal path4 overloaded linksUnderutilization!

9 underutilized links

D

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D

Traffic Engineering

Allows traffic distribution

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Traffic Engineering

D

No conge-stion

Uniform use

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Can you do it with traditional IP routing? Traffic for D on

optimal path4 overloaded links9 underutilized links

D

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It is necessary to choose paths according to load

Traffic for D on optimal pathoverloaded linksunderutilized links

D

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In such way, unloaded links are loadedand viceversa ...

Traffic for D on optimal pathoverloaded linksunderutilized links

D

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... and routing tables change ... Traffic for D on

optimal pathoverloaded linksunderutilized links

D

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…so does the link load...Traffic for D on optimal pathoverloaded linksunderutilized links

D

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... and the paths change again!!! Traffic for D on

optimal pathoverloaded linksunderutilized links

D

Instability!

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Traffic Engineering with MPLS

D

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ATM has so far been used for traffic engineering on IP networks

Two control plans

Routers are ATM-unaware

Great number of adjacencies

Limitated scalability

Traffic Engineering without MPLS

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Only one control plan operating on physical topology

Simpler

Greater scalability

MPLS is IP-aware

Traffic Engineering with MPLS

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MPλS (MPLambdaS)

MPLS control plans in optical networks

GMPLS (Generalized MPLS)

MPLS control plane in any network

Packet, circuit, optics, etc…

MPLS extensions

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Adding CoS and QoS

Explicit support is required in LSR data plan and control

plan

Resources and service modes may be associated to a FEC at

LSP setup

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Class of service (CoS)

Relative priority among different FECs

It does offer absolute guaranties

Support of DiffServ model

Per-hop behavior

EF (expedite forwarding), AF (assured forwarding)

Traffic engineering for class

DS-aware traffic engineering

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Quality of service (QoS)

Specific guaranties on

Bandwidth

Delay

Burst size

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Advantages of QoS in MPLS

Unified network supporting all types of services

(marketing message)

Support of QoS and real-time services on IP (e.g., voice) is not ready

Alot of multi-service networks now have a paradigm “Ships-in-the-night”

ATM protocols are ATM typical services

MPLS control plan for IP services

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Header Layer 2 IP packetLabel 3

MPLS Domain 3

Label 2

MPLS Domain 2

Label 1

MPLS Domain 1

Label Stackhierarchy and scalability

• Routing table reduction

• Forwarding table reduction

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MPLS and scalability

MPLS labels introduce hierarchy

Various hierarchical levels, as needed for the necessary scalability

Routing tables of transit routers do not have to be comprehensive

LSP between edge routers

Simpler and faster exact match of labels rather than longest prefix matching

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VPN: Virtual Private Network

Services similar to those of a private network, but provided on a public

infrastructure (IP)

Privacy and security

Overlapping addressing spaces (private)

Non-unique addresses

Class of Service (CoS) and Quality of Service (QoS)

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VPN based on MPLS

The labels “hide” IP addresses of users on the public network

MPLS allows a scalable solution for VPN services

Other approaches require explicit setting (manual) of tunnels between each pair of websites

Number of VPNs

Number of VPN members

Service flexibility (thanks to FEC)

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Standardization

IETF –Internet Engineering Task Force

FR/MPLS Alliance

MPLS working group

Consortium of producersSpeed up spreadingAspects omitted by IETF

VoMPLS, ADSL

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BibliographyT. Tofoni, “MPLS – Fondamenti e applicazioni alle reti IP”, Hoepli, 2003

IETF MPLS Working Group, http://www.ietf.org/html.charters/mpls-charter.html

E. Rosen, A. Viswanathan, R. Callon, “Multiprotocol Label Switching Architecture,” RFC 3031, Standards Track, Jan. 2001

E. Rosen, D. Tappan, G. Fedorkow, Y. Rekhter, D. Farinacci, T. Li, A. Conta, “MPLS Label Stack Encoding,” RFC 3032, Standards Track, Jan. 2001

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Bibliography

F. Le Faucheur, et al., “Multi-Protocol Label Switching (MPLS) Support of Differentiated Services,” RFC 3170, Standards Track, May 2002

Davie, B., Lawrence, J., McCloghrie, K., Rekhter, Y., Rosen, E., Swallow, G. and P. Doolan, "MPLS using LDP and ATM VC Switching", RFC 3035, January 2001.

Andersson, L., Doolan, P., Feldman, N., Fredette, A. and B. Thomas, "LDP Specification", RFC 3036, January 2001.