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MPLS Tutorial ETSI June 99. Francois Le Faucheur Systems Architect Cisco Systems [email protected] Agenda. Label Switching Technology Overview History & Motivation Destination-Based Routing Label Distribution Protocol(s) Encapsulation MPLS Over ATM Applications Quality of Service

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Mpls tutorial etsi june 99 l.jpg

MPLS TutorialETSI June 99

Francois Le Faucheur

Systems Architect

Cisco Systems

[email protected]

Cisco Systems


Agenda l.jpg
Agenda

  • Label Switching Technology Overview

    • History & Motivation

    • Destination-Based Routing

    • Label Distribution Protocol(s)

    • Encapsulation

    • MPLS Over ATM

  • Applications

    • Quality of Service

    • Traffic Engineering

    • VPNs

  • Conclusion: Gbit Routing or MPLS?

Cisco Systems


Label switching motivation l.jpg
Label Switching Motivation

  • Address major network evolution problems:

    • Throughput

    • Scaling

      • Number of nodes, flows, routes

    • Traffic engineering (explicit routes)

  • Permit graceful evolution of routing

    • Flexibility, new applications

  • Simplify integration of ATM and IP

Cisco Systems


Label switching basics l.jpg
Label Switching Basics

  • Combines Layer 3 routing with label-swapping forwarding

    • Simplicity of Layer 2 forwarding offers high performance

    • Layer 3 routing has proven scalability

  • Clean separation of Forwarding and Control/Routing

    • Forwarding component: Simple label-swapping paradigm

    • Control component: Collection of modules to maintain and distribute label bindings

    • Separation leads to graceful evolution of control paradigm

Cisco Systems


Label switching devices l.jpg
Label Switching Devices

Label Switching Routers (LSRs)

(ATM Switch or Router)

Label Edge Routers

Cisco Systems


Forwarding component l.jpg
Forwarding Component

  • Label Forwarding Information Base (LFIB)

    • Each entry consists of:

      • Incoming label

      • One or more sub-entries:

        • Outgoing label, outgoing interface, outgoing MAC address

    • LFIB is indexed by incoming label

Cisco Systems


Forwarding component cont l.jpg
Forwarding Component (Cont.)

  • Forwarding algorithm:

    • Extract label from a packet

    • Find LFIB entry withincoming label = label from packet

    • Replace label in packet with outgoing label(s)

    • Send packet on outgoing interface(s)

  • Observation: forwarding algorithm is

    • Network Layer-independent

    • independent of how labels have been assigned (ie by Control module)

Cisco Systems


Label switching example l.jpg

128.89.10

1

128.89.10

0

171.69

1

171.69

1

...

...

Label Switching Example

Destination-Based Routing Module

Address

Prefix

Address

Prefix

Interface

Interface

128.89.10

Advertises Reachability

to 128.89.10

i/f 0

i/f 1

i/f 1

Advertises Reachability to 128.89.10 and 171.69

171.69

Advertises Reachability

to 171.69

Cisco Systems Confidential

0675_03F7_c3

10


Label switching example cont l.jpg

128.89.10

1

128.89.10

0

171.69

1

171.69

1

...

...

Label Switching Example (Cont.)

Address

Prefix

Address

Prefix

Interface

Interface

128.89.10

Advertises Binding

<5,128.89.10> Using LDP

i/f 0

i/f 1

i/f 1

Advertises Bindings

<3,128.89.10>

<4,171.69> Using LDP

171.69

Advertises Binding

<7,171.69> Using LDP

11


Label switching example cont10 l.jpg

Local

Label

Remote

Label

Address

Prefix

Local

Label

RemoteLabel

Address

Prefix

Interface

Interface

Label Switching Example (Cont.)

128.89.10

0

3

5

128.89.10

1

x

3

4

7

171.69

1

x

4

171.69

1

...

128.89.10

...

0

1

1

7

171.69.12.1

data

171.69.12.1

data

4

171.69.12.1

data

171.69

‘Edge’ Router Does

Longest Match, Adds Label

Subsequent Routers

Forward on Label Only

Cisco Systems


Label distribution protocol ldp l.jpg
Label Distribution Protocol (LDP)

  • Used to distribute <label,prefix> bindings

  • Incremental updates over reliabletransport

  • One of several label-binding mechanisms

Cisco Systems


Frame encapsulation l.jpg

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Label | Exp |S| TTL |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Frame Encapsulation

  • Can be used over Ethernet, 802.3, or PPP links

  • new Ethertypes/PPP PIDs

  • Contains everything needed at forwarding time

  • MPLS Headers can be used “recursively”

S = Bottom of Stack

TTL = Time to Live

EXP = Experimental (formerly COS = Class of Service)

Cisco Systems


Label switching and atm l.jpg
Label Switching and ATM 3

  • label switching forwarding:

    • Make decision using fixed length label

    • Rewrite the label with a new value

    • Sounds like ATM

  • label switching control:

    • Based on L3 protocols

    • used to set-up/maintain ATM VCs (instead of traditional ATM Control plane protocols UNI/PNNI)

    • Resolves ‘impedance mismatch’

Cisco Systems


Label distribution for atm downstream on demand l.jpg
Label Distribution for ATM 3Downstream on Demand

Output

i/f

Local

Label

Address

Prefix

Remote

Label

Input

i/f

Requests a labelfor 128.89

128.89

0

1

5

7

6

0

2

8

128.89

...

128.89

Requests Two Labels for 128.89

Returns a Label to Each Requester

Requests a labelfor 128.89

Label Switching = ATM switching

because labels copied in VCI

Cisco Systems


Mpls atm impedance mismatch l.jpg
MPLS ATM Impedance Mismatch 3

  • Downstream on Demand

    • label conservation

  • VC-Merge

    • Cell Interleave

  • Loop prevention

    • Hop count fields in request and response

    • Per-VC queuing to limit damage

    • loop detection

    • optional loop prevention

  • TTL semantics

    • Decrement by hop count on ingress

    • Use ‘router alert’ to handle traceroute

Cisco Systems


Scaling in l2 l3 networks l.jpg
Scaling in L2/L3 Networks 3

Problem: Huge Number of Routing Adjacencies

Impacts Routing Performance

Cisco Systems


Scaling in mpls networks l.jpg
Scaling in MPLS Networks 3

Solution: Only Neighbor-Neighbor

Routing Adjacencies

Cisco Systems


Agenda18 l.jpg
Agenda 3

  • Label Switching Technology Overview

    • History & Motivation

    • Destination-Based Routing

    • Label Distribution Protocol(s)

    • Encapsulation

    • MPLS Over ATM

  • Applications

    • Quality of Service

    • Traffic Engineering

    • VPNs

  • Conclusion: Gbit Routing or MPLS?

Cisco Systems


Mpls qos l.jpg
MPLS QoS 3

  • MPLS targets support of existing IETF QoS models (does not reinvent a new QoS model):

    • Diff-Serv over MPLS

    • Int-Serv over MPLS

  • targeted result is end-to-end IP QoS through MPLS clouds indistinguishable from IP QoS in non-MPLS network

Cisco Systems


Diff serv on atm lsrs l.jpg
Diff-serv on ATM-LSRs 3

  • Challenges:

    • No DS field in header

    • Re-ordering constraints of Diffserv

    • Different drop algorithms in switches (ie no RED/WRED)

  • Solution approach:

    • Use parallel LSPs to one destination (FEC)

    • Each LSP represents a group of PHBs (ie the PHBs with ordering constraint)eg. EF, Default, AF1x, AF2x, AF3x, AF4x

      --> one LSP per <FEC, PHB group>

    • CLP to indicate drop preference within PHB group

Cisco Systems


Parallel lsps l.jpg
Parallel LSPs 3

EF

  • PHB Group (ie EF, AF1x, AF2x,..) signaled at label establishment time

  • Switch performs scheduling based on PHB Group :

    • eg. all AF1x labels into the same queue

    • eg. Switches perform per-class WFQ (not per-VC)

  • Switch performs “drop precedence” based on CLP bit

AF1

AF2

Cisco Systems


Diff serv on ppp lsr l.jpg
Diff-Serv on PPP LSR 3

  • Two complementary approaches pursued and allowed simultaneously

  • Similar to Diff-Serv over ATM LSR

    • ie Parallel LSPs

    • PHB Group is signaled at LSP set-up

    • use MPLS Shim Header EXP field to convey Drop Precedence

  • use MPLS EXP field exactly as DSCP is used for IP

    • takes advantage of fact that MPLS EXP field is seen at every PPP LSR hop

    • use MPLS EXP field to indicate the PHB Group as well as the Drop Precedence

    • limit to total 8 PHBs

Cisco Systems


Int serv over mpls l.jpg
Int-Serv over MPLS 3

  • Each RSVP session has dedicated label

    • label binding carried in RSVP RESV and PATH messages

    • Enables simple flow classification (label vs. src and dest address and port)

    • Note: this is for establishment of a label per RSVP flow (as opposed to using RSVP to set up labels for fat aggregates for Traffic Engineering)

  • Stable I-D but not high priority of MPLS group

Cisco Systems


Agenda24 l.jpg
Agenda 3

  • Label Switching Technology Overview

    • History & Motivation

    • Destination-Based Routing

    • Label Distribution Protocol(s)

    • Encapsulation

    • MPLS Over ATM

  • Applications

    • Quality of Service

    • Traffic Engineering

    • VPNs

  • Conclusion: Gbit Routing or MPLS?

Cisco Systems


Ip routing the fish l.jpg
IP Routing & “the Fish” 3

R8

R3

R4

R5

R2

R1

R6

R7

IP (Mostly) Uses Destination-Based Least-Cost Routing

Flows from R8 and R1 Merge at R2 and Become Indistinguishable

From R2, Traffic to R3, R4, R5 Use Upper Route

Alternate Path Under-Utilized

6


Mpls traffic engineering l.jpg
MPLS Traffic Engineering 3

  • MPLS TE is not about offering additional QoS services visible by end-user

  • MPLS TE is about reducing cost of providing end-user services (eg Diff-Serv) through better use of given resources

  • May improve QoS

  • MPLS TE takes advantage of “connection-like” nature of MPLS to distribute traffic based on Bandwidth demand/use

  • like current Voice Traffic Engineering

Cisco Systems


Mpls te tunnel l.jpg
MPLS TE Tunnel 3

R8

R3

R4

R5

R2

R1

R6

R7

Labels, like ATM VCs can be used to establish virtual circuits which are “Qos Routed”

Normal Route: R1->R2->R3->R4->R5

TE Tunnel: R1->R2->R6->R7->R4->R5

0401_10F8_c1

NW97_EMEA_504

6


Mpls te l.jpg
MPLS TE 3

  • TE Tunnels need be “automatically” routed

  • performs Constraint Based Routing where constraints include:

    • Bandwidth need of a tunnel versus bandwidth available on all links

    • Policy constraint configurable by Operator (eg that sort of Tunnel must not use that sort of links)

Cisco Systems


Te example deployment l.jpg

POP4 3

POP

POP

POP

POP2

POP1

TE Example Deployment

Find route & set-up tunnel for 20 Mb/s from POP1 to POP4

Find route & set-up tunnel for 10 Mb/s from POP2 to POP4

WAN area

Cisco Systems


Mpls te components 1 l.jpg
MPLS TE Components (1) 3

  • Link state IGP protocols enhanced to advertise “unreserved capacity” per link

  • SPF computation enhanced to route a TE tunnel (Constraint based Routing):

    • first prune the links which do not satisfy a constraint from the topology

    • Pick shortest path on the remaining topology

Cisco Systems


Mpls te components 2 l.jpg
MPLS TE Components (2) 3

  • Tunnel set-up (ie label binding) along the route computed by Constraint Base Routing:

    • via RSVP with extensions (eg Explicit Route Object), Note: RSVP state applies to a large aggregate of flows (i.e. a tunnel), rather than to a single flow or

    • via CR-LDP (ie extensions over LDP such as Explicit Route TLV)

Cisco Systems


Mpls te components 3 l.jpg
MPLS TE Components (3) 3

  • MPLS LFIB handles the forwarding “as usual”

    • only LFIB has been populated by another Control module than Destination Based LDP)

  • IGP enhanced on tunnel Head-ends to “route” IP packets “into” TE tunnels

Cisco Systems


Traffic engineering summary l.jpg
Traffic Engineering Summary 3

  • Connection-like aspects of MPLS allow traffic engineering for IP

  • Addresses limitations of connectionless routing

  • Avoids drawbacks of overlay (L2/L3) model

  • Combination with constraint-based routing provides automatic tunnel setup which maximises usage of existing resources and re-optimization on topology change

  • Underlying mechanism to achieve IP QoS more efficiently

  • In core, uses unmodified label switching Forwarding component

Cisco Systems


Agenda34 l.jpg
Agenda 3

  • Label Switching Technology Overview

    • History & Motivation

    • Destination-Based Routing

    • Label Distribution Protocol(s)

    • Encapsulation

    • MPLS Over ATM

  • Applications

    • Quality of Service

    • Traffic Engineering

    • VPNs

  • Conclusion: Gbit Routing or MPLS?

Cisco Systems


Scalability issues of layer 2 vpns l.jpg
Scalability issues of Layer 2 VPNs 3

  • Complexity of provisioning n2 VCs per VPN, along with QOS for each VC

  • Complexity of designing routing system for each VPN over full VC mesh

  • Poor routing performance over mesh of adjacencies

  • Poor bandwidth efficiency if mesh is not used

Cisco Systems


Why mpls vpns l.jpg
Why MPLS VPNs? 3

  • MPLS combines L3 routing and L2 forwarding

  • L3 routing provides

    • improved scalability by eliminating mesh of connections from CPE-to-CPE

  • L2 (label-based) forwarding provides

    • comparable security to L2 approaches

    • hiding of non-registered addresses

  • Hierarchical labels (label stack) further enhance scalability

Cisco Systems


Vpn example l.jpg
VPN - example 3

VPN A/Site 2

VPN B/Site 1

CEA2

CE1B1

CEB2

VPN B/Site 2

P1

PE2

CE2B1

MPLS

P2

PE1

PE3

CEA3

CEA1

P3

CEB3

VPN A/Site 3

VPN A/Site 1

VPN B/Site 3

Cisco Systems


Basic ingredients l.jpg
Basic ingredients: 3

  • Constrained distribution of routing information w/ BGP

  • VPN-IP addresses

  • Multiprotocol Label Switching (MPLS)

    • in backbone, LFIB Forwarding “as usual”

  • Peer Model

Cisco Systems


Vpn example39 l.jpg
VPN - example 3

VPN A/Site 2

VPN B/Site 1

CEA2

CE1B1

CEB2

VPN B/Site 2

P1

PE2

Single

Routing

Adjacency

VPN<-->Cloud

CE2B1

iBGP (VPN-IPv4 @)

MPLS

P2

PE1

PE3

LDP

CEA3

Two-level

labelled packets

CEA1

CEB3

VPN A/Site 3

VPN A/Site 1

VPN B/Site 3

Cisco Systems


Agenda40 l.jpg
Agenda 3

  • Label Switching Technology Overview

    • History & Motivation

    • Destination-Based Routing

    • Label Distribution Protocol(s)

    • Encapsulation

    • MPLS Over ATM

  • Applications

    • Quality of Service

    • Traffic Engineering

    • VPNs

  • Conclusion: Gbit Routing or MPLS?

Cisco Systems


A perception problem l.jpg
A Perception Problem 3

  • A lot of people think label switching is all about forwarding performance

    • ATM switches used to be faster than routers

    • Plenty of label switching marketing reinforced this

  • This causes Gbit router implementors to say `Ha! Label Switching is useless’ as routers catch up

  • If standard IP forwarding at Gbit speeds is the only requirement, Gbit routers are the solution

Cisco Systems


The value of label switching l.jpg
The value of label switching 3

  • Label switching adds value to Gbit routers

    • Traffic engineering support

    • VPNs

    • Ease of evolution

  • Label switching enables better IP/ATM integration

    • only relevant if ATM core was chosen for some reason, e.g. service integration

  • Not too hard to add label switching to Gbit routers

Cisco Systems


References l.jpg
References 3

  • Diffserv

    • RFC 2474. Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers. K. Nichols et al.

    • RFC 2475. An Architecture for Differentiated Service. S. Blake et al.

  • MPLS Basics

    • draft-ietf-mpls-arch-04.txt

    • draft-ietf-mpls-atm-01.txt

    • draft-ietf-mpls-ldp-03.txt

  • MPLS Traffic Engineering & DiffServ

    • draft-ietf-mpls-rsvp-lsp-tunnel-02.txt

    • draft-ietf-mpls-traffic-eng-00.txt

    • draft-ietf-mpls-cr-ldp-01.txt

    • draft-ietf-mpls-diff-ext-00.txt

    • draft-davari-mpls-diff-ppp-00.txt

  • MPLS VPNs

    • RFC 2547. BGP/MPLS VPNs. E. Rosen, Y. Rekhter. March 1999.

Cisco Systems


References44 l.jpg
References 3

  • Gigabit routers

    • Partridge et al. “A 50-Gb/s IP router," IEEE/ACM Transactions on Networking, vol. 6, June 1998.

  • Fast Routing Lookups

    • Brodnik et al. “Small Forwarding Tables for Fast Routing Lookups”, Sigcomm ‘97.

    • Waldvogel et al. “Scalable High Speed IP Routing Lookups”, Sigcomm ‘97.

    • Srinivasan et al. “Fast Scalable Level 4 Switching”, Sigcomm '98.

    • Lakshman and Stiliadis, "High Speed Policy Based-Packet forwarding...", Sigcomm '98.

  • MPLS

    • Davie et al. “Switching in IP Networks”, Morgan Kaufmann Publishers, May 1998.

    • Rekhter et al. “Tag Switching Architecture Overview”, IEEE Proceedings, vol 85, No. 12, Dec 1997.

Cisco Systems


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