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© M. Baldi: see page 2MPLS - 1

MPLSMulti-protocol label switching

MPLSMulti-protocol label switching

Mario BaldiPolitecnico di Torino

(Technical University of Torino)

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

Mario BaldiPolitecnico di Torino

(Technical University of Torino)

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


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

Network

From MPLS Forum DocumentsFrom MPLS Forum Documents


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”


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, MPLSThe future: WDM, IP, MPLS


The ideaThe idea

Instead of the IPdestination addressInstead of the IP

destination address

Forwarding packets according to a labelForwarding packets according to a label

LabelLabel IP packetIP packet


Why?Why?

The label may be used as an indexThe label may be used as an index

Faster lookupFaster lookup

Traffic engineeringTraffic engineering

Instead of longest prefix matchingInstead of longest prefix matching


MPLS introduces a connection-oriented

paradigm in IP networks

MPLS introduces a connection-oriented

paradigm in IP networks


Network architectureNetwork architecture

Label edge routerIngress/egress LSRLabel edge routerIngress/egress LSR

Label switch router (LSR)Label switch router (LSR)

MPLS networkMPLS cloud

MPLS networkMPLS cloud


Egress LSREgress LSR

Ingress LSRIngress LSR

Label Switched Path (LSP)Label Switched Path (LSP)


Label switchingLabel switching

DD

DD

11223344

0033

00

1122

33

0011

00

22

AA

DD

XX

00

00

11

11

InIn OutOut

22

22

11

InIn OutOut

00

11

InIn OutOut

00

11InIn OutOut

00

11112222

00

DD


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


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


MPLS “header”MPLS “header”

Contains the labelContains the label

MPLS key elementsMPLS key elements

Upgraded routing protocolsUpgraded routing protocols

Constraints in choosing pathsConstraints in choosing paths

Protocols for label distribution Protocols for label distribution

SignalingSignaling


Shim headerShim headerMPLS headerMPLS header

Level 2Level 2 IP packetIP packet

LabelLabel ExpExp SS TTLTTL20 bit20 bit 3 bit3 bit 8 bit8 bit11

TTL: Time to liveTTL: Time to live

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


VCI/VPI (ATM)VCI/VPI (ATM)

MPLS labels in layer 2 headerMPLS labels in layer 2 header

Connection oriented layer 2protocols

Connection oriented layer 2protocols

ATM and frame relayATM and frame relay

DLCI (Frame relay)DLCI (Frame relay)


Forwarding equivalence class (FEC)Forwarding equivalence class (FEC)

Packets thatPackets that

Follow the same pathin MPLS network

Follow the same pathin MPLS network

Are treated the same wayby each LSR

Are treated the same wayby each LSR

Receive the same label Receive the same label


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


Input labelInput label

Output portOutput port

LSP CreationLSP Creation

Label MappingLabel Mapping

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

belonging to a FEC is associated to

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

belonging to a FEC is associated to


Downstream Label BindingDownstream Label Binding

Label DistributionLabel 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 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

The label is communicated to the upstream switch

Label mapping for the corresponding portLabel mapping for the corresponding port


Static label binding (and mapping)Static label binding (and mapping)

Through managementThrough management

Non-scalableNon-scalable

Equivalent to PVC ATMEquivalent to PVC ATM

No interoperability among managing systemsNo interoperability among managing systems

Impossible to have LSPs through different networksImpossible to have LSPs through different networks


Dynamic label bindingDynamic label binding

Protocol (IP) drivenProtocol (IP) driven

Explicit creation of LSPExplicit creation of LSP

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

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

Explicit signalingExplicit signaling

Initiated by label edge routersInitiated by label edge routers


Routing protocol: BGPRouting protocol: BGP

Only protocol drivenOnly protocol driven

Designed for allocation in integrated service networksDesigned for allocation in integrated service networks

Resource reservation protocol (RSVP)Resource reservation protocol (RSVP)

Label distribution protocolsLabel distribution protocols

Three alternatives (incompatible)Three alternatives (incompatible)

Label distribution protocol (LDP)Label distribution protocol (LDP)

Designed for the purposeDesigned for the purpose


Routing protocolsRouting protocols

Used to determine LSP routingUsed to determine LSP routing

Guide label binding proceduresGuide label binding procedures

They indirectly determine packet routingThey indirectly determine packet routing


carry topology informationcarry topology information


Existing protocolsExisting protocols

IS-ISIS-IS

OSPFOSPF

BGP-4BGP-4

In MPLS context

they are enhanced d to...

In MPLS context

they are enhanced d to...



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

routing decisions (constraint data)

Capacity of linksCapacity of links

Link utilizationLink utilization

Dependencies among linksDependencies among links

Used for fault recoveryUsed for fault recovery


Enhanced routing protocolsEnhanced routing protocols

Constraint based routingis fundamental to support

traffic engineering

Constraint based routingis fundamental to support

traffic engineering

IS-IS–TEIS-IS–TE

OSPF–TEOSPF–TE


Similar to routing for IP packetsSimilar to routing for IP packets

Ingress and egress labelsIngress and egress labels

Switches agree on corrispondencies amongSwitches agree on corrispondencies among

Each switch decides the next stepof LSP path

Each switch decides the next stepof LSP path

Hop-by-hop routingHop-by-hop routing

Labels and FECLabels and FEC


The choice is constraint basedThe choice is constraint based

Constraint based routingConstraint based routing

Explicit constraint based routingExplicit constraint based routing

For example, LSR ingressFor example, LSR ingress

A single switch may choose the path of an LSPA single switch may choose the path of an LSP

Explicit routingExplicit routing


CR-LDPCR-LDP

Constraint-based routing LDPConstraint-based routing LDP

Should be modified Should be modified

Label distribution protocolsLabel distribution protocols

RSVP-TERSVP-TE

RSVP for Traffic EngineeringRSVP for Traffic Engineering

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

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


New possibilitiesNew possibilities

Traffic engineeringTraffic engineering

Per-class traffic engineeringPer-class traffic engineering

Guaranteed quality of serviceGuaranteed quality of service

Fast fault recoveryFast fault recovery

Not yet supportedNot yet supported

In less than 50 msIn less than 50 ms

Synergy with DiffServSynergy with DiffServ


Control plane and data planeControl plane and data plane

Data planeData Data planeplane

Control planeControl Control planeplane

RIPRIP IGRPIGRP

OSPFOSPF

BGPBGPISIS--ISIS

Routing databaseRouting database

RoutingtableRoutingtable

Continuous updating

Continuous updating

IPIP


Control plane and data planeControl plane and data plane

DataplaneDataDataplanplanee

Control planeControl planControl planee

RIPRIPIGRPIGRP

OSPFOSPF

BGPBGP

ISIS--ISIS

Routing databaseRouting database

Forwarding tableForwarding table

MPLSMPLS

LDPLDPRSVPRSVP

LSP setupLSP setup

Signaling (LSP setup)Signaling (LSP setup)

Routingtable

Routingtable


Traditional IP routingTraditional IP routingTraffic for D on optimal pathTraffic for D on optimal path

DD

Aggregation!Aggregation!


Traditional IP routingTraditional IP routing

DD

Traffic for D on optimal pathTraffic for D on optimal path

4 overloaded links4 overloaded linksConConggestion!estion!


Traditional IP routingTraditional IP routingTraffic for D on optimal pathTraffic for D on optimal path

4 overloaded links4 overloaded linksUnderUnderutilizationutilization!!

9 underutilized links9 underutilized links

DD


DD

Traffic EngineeringTraffic Engineering

Allows traffic distributionAllows traffic distribution


Traffic EngineeringTraffic Engineering

DD

No No congeconge--stionstion

Uniform Uniform useuse


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

optimal pathTraffic for D on optimal path

4 overloaded links4 overloaded links

9 underutilized links9 underutilized links

DD


It is necessary to choose paths according to loadIt is necessary to choose paths according to load


overloaded linksoverloaded links

underutilized linksunderutilized linksDD


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

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



underutilized linksunderutilized links

DD


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




DD


…so does the link load...…so does the link load...Traffic for D on optimal pathTraffic for D on optimal path



DD


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




DD

Instability!Instability!


Traffic Engineering with MPLSTraffic Engineering with MPLS

DD


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 MPLSTraffic Engineering without MPLS


Only one control plan operating on physical topology

Simpler

Greater scalability

MPLS is IP-awareMPLS MPLS isis IPIP--awareaware

Traffic Engineering with MPLSTraffic Engineering with MPLS


MPλS (MPLambdaS)

MPLS control plans in optical networks

GMPLS (Generalized MPLS)

MPLS control plane in any network

Packet, circuit, optics, etc…

MPLS extensionsMPLS extensions


Adding CoS and QoS

Explicit support is required in LSR data plan and control

plan

Explicit support is required Explicit support is required in LSR data plan and control in LSR data plan and control

planplan

Resources and service modes may be associated to a FEC at

LSP setup


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


Quality of service (QoS)

Specific guaranties on

Bandwidth

Delay

Burst size


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


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

• Routing table reduction

• Forwarding table reduction


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


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)


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)


StandardizationStandardization

IETF –Internet Engineering Task ForceIETF –Internet Engineering Task Force

FR/MPLS AllianceFR/MPLS Alliance

MPLS working groupMPLS working group

Consortium of producersConsortium of producersSpeed up spreadingSpeed up spreadingAspects omitted by IETFAspects omitted by IETF

VoMPLS, ADSLVoMPLS, ADSL


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


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.