Internet Routing - MPLS - Massey University .Internet Routing - MPLS By Richard Harris. Semester

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Transcript of Internet Routing - MPLS - Massey University .Internet Routing - MPLS By Richard Harris. Semester

Internet Routing - MPLS

By

Richard Harris

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 2

MPLS Presentation Outline

Introduction Problems of Internet size

Methods for overcoming potential problems

What is MPLS? Overview

MPLS terminology

MPLS Architecture The label stack

Label Switching Protocols

MPLS Signalling Protocols

Traffic Management in MPLS

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 3

Introduction

Huge growth in the Internet Figures vary from 2x to 10x per annum for traffic growth!

Major ISPs (Internet Service Providers) have copedwith this growth in a variety of different directions,viz: Network architecture

Capacity expansion

Traffic management methods (Traffic Engineering)

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 4

Network Architecture

This approach entails Development of scalable network architectures

Defining suitable network topologies and structures

Identification of abstract objects and classes within thenetwork.

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 5

Capacity Expansion

Most ISPs started with backbonecapacities in the range of 44Mbps(in the USA this is DS3) during1996.

By 1999, the capacities used wereabout 622Mbps

A recent announcement shows thatISPs are now introducing capacitiesin the region of 9.9Gbps (referred toas OC-192c) and using DWDM(Dense WDM).

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 6

Traffic Management/Engineering

This direction is required because the previous twoapproaches are insufficient to solve the growthproblem mentioned in the introduction!

Architectures and capacity expansion cannot providethe high quality Internet services that are now beingdemanded by the many different customers of thisnetwork.

Traffic engineering deals with performanceoptimisation issues and it has been realised howimportant this aspect is for operating such a hugemultipurpose network.

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 7

Traffic Engineering Limitations of theexisting Internet - 1

Historically difficult to perform effective trafficengineering and management of Internet traffic.

IP was conceived as a best effort service.

Shortcomings of IP technologies: Lack of measurement capabilities

Limitations of intra-domain routing control functions.

Routing protocols like OSPF, EIGRP, IGP etc work ontopology-driven per-packet progressive connection control.Each router makes independent decisions using a localversion of a routing area link state database.

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 8

Traffic Engineering Limitations of theexisting Internet 2

Route selection is based on shortest path calculations usingsimple additive link metrics.

This approach is highly distributed and scalable, but flawed,because these protocols do not consider the characteristics ofthe offered traffic and the network capacity constraints whenmaking routing decisions.

Subsets of network resources become congested.

Alternate paths become under-utilised.

This suggests that there is poor resource allocation taking place.

Traffic engineering is required to fix these problems.

MPLS to the rescue!

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 9

What will MPLS do?

Multi Protocol Label Switching (MPLS) isexpected to

improve the price/performance of network layerrouting,

improve the scalability of the network layer,

provide greater flexibility in the delivery of (new)routing services (by allowing new routing servicesto be added without a change to the forwardingmechanism).

History

MPLS was originally proposed by a group of engineers from IpsilonNetworks, but their "IP Switching technology, which was defined onlyto work over ATM, did not achieve market dominance. Cisco introduceda related proposal, not restricted to ATM transmission, called "TagSwitching".

It was a Cisco proprietary proposal, and was renamed "LabelSwitching". It was handed over to the IETF for open standardization.

One original motivation was to allow the creation of simple high-speedswitches, (Initially it was impossible to forward IP packets entirely inhardware.)

The advantages of MPLS primarily revolve around the ability to supportmultiple service models and perform traffic management.

MPLS also offers a robust recovery framework.

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 10

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 11

What is MPLS? - 1

MPLS is a technique for combining the best features of IP andATM, viz: IP routing ATM throughput

It borrows heavily from methods used in ATM to rapidly transfercells across the network. Supports destination oriented, multicast and hierarchical routing Supports explicit routing Label-transport, Label-stack Quality of Service (QoS)

MPLS is not a specific layer 3 protocol it appears to lie betweenlayers 2 and 3.

MPLS supports many other layer 2 technologies (Frame Relay,ATM, Ethernet, Token Ring)

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 12

What is MPLS? - 2

A key concept of MPLS is the separation of an IP routersfunctions into two parts:

Forwarding

Control

Forwarding:

Responsible for how data packets are relayed between the networkrouters. It uses label swapping similar to ATM switches that useVirtual Path/Virtual Circuit identifiers although MPLS may beregarded as more general than VPI/VCI.

A label is a short fixed length number, independent of the network layer.

Label swapping essentially involves a table lookup of a packets label todetermine its route and new label value. It is much simpler thanprevious methods.

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 13

What is MPLS? - 3

A router capable of MPLS is known as a LabelSwitching Router (LSR).

A set of Label Switching Routers traversed by apacket is called a Label Switched Path (LSP).

A contiguous set of LSPs under a singleadministration is known as an MPLS domain.

A packet is transmitted across an MPLS domainbased only on its label.

Packet Label

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 14

Some MPLS Terminology

LDP: Label Distribution Protocol

LSP: Label Switched Path

FEC: Forwarding Equivalence Class

LSR: Label Switching Router

LER: Label Edge Router

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 15

MPLS Label

The label can: use an existing layer 2 header label (eg the VPI/VCI field in

the ATM cell header) or

inserted between the layer 2 and IP headers as a small shimlabel like the following:

20-bits: Label value used by LSR to lookupeither next-hop, operation to perform, or

outgoing data-link encapsulation

Label Value S

8-bits: TTLdecrementedby each LSR

Time-to-Live(TTL)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

1-bit: "Bottomof Label

Stack" Flag

Type ofservice

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 16

Route at edge, switch in core

IP ForwardingLABEL SWITCHINGIP Forwarding

IP IP #L1 IP #L2 IP #L3 IP

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 17

Label Switched Path (LSP)

IntfIn

LabelIn

Dest IntfOut

3 0.40 47.1 1

IntfIn

LabelIn

Dest IntfOut

LabelOut

3 0.50 47.1 1 0.40

47.1

47.247.3

1

2

31

2

1

2

3

3IntfIn

Dest IntfOut

LabelOut

3 47.1 1 0.50

IP 47.1.1.1

IP 47.1.1.1

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 18

- ER-LSP follows a route that the source chooses. Inother words, the control message to establish the LSP(label request) is source routed.

#216

#14

#462

#972

#14 #972

A

B

C

Route={A,B,C}

Explicitly routed or ER-LSP

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 19

IntfIn

LabelIn

Dest IntfOut

3 0.40 47.1 1

IntfIn

LabelIn

Dest IntfOut

LabelOut

3 0.50 47.1 1 0.40

47.1

47.247.3

1

2

3

1

2

1

2

3

3

In t fIn

D e s t In tfO u t

L a b e lO u t

3 4 7 .1 .1 2 1 .3 33 4 7 .1 1 0 .5 0

IP 47.1.1.1

IP 47.1.1.1

Explicitly Routed LSP (ER-LSP)

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 20

ER LSP - advantages

Operator has routing flexibility (policy-based, QoS-based)

Can use routes other than shortest path

Can compute routes based on constraints in exactlythe same manner as ATM based ondistributed topology database.(traffic engineering)

Semester 1 - 2010 Advanced Telecommunications 143.466 Slide 21

MPLS Label Stack

Stack is LIFO

Depth n stack illustrated below:

Label n

Label n-1

Label 2

Label 1 1 Last label

Push stackPop stack

Semester 1 - 2010 Advanced Telecommunicatio