MPLS: The Magic Behind the Myths

Grenville Armitage

Lucent Technologies

Introduction

Reviews key differences (and similarities) between IP routing and emerging MPLS approach

Article highlights MPLS does not offer much as once portrayed – e.g. gigabit forwarding

Fails to point out flaws in vision Contribution related to traffic engineering

Scalability Issues

MPLS provides traffic engineering capabilities – agreed

Benefits of MPLS extend only as far as its deployment

End-to-end solution possible only if entire network MPLS enabled

MPLS is domain specific!

Scalability Issues (contd.)

VoIP packet

Supports MPLS

No MPLS

No QoS guarantee

MPLS is domain specific!!

Stateful Routers

LSR (label-switching routers) keep info about different labels

Labels correspond to states stored in router Routers that keep information are bad Does not mention how to deal with failures

Stateful Routers

12

4

3

PP

??

Lose label information

Loss of Label makes packet Unroutable!

Control and Management

Unclear how QoS characteristics of each LSP managed

Unclear how non-shortest paths for traffic engineering obtained

Human intervention required for router configuration

Complex and error-prone

MPLS not for QoS

Domain specificity and scalability issues in deployment

No standards to designate Type of Service (TOS) bits

MPLS has no end-to-end solution MPLS suffers from static routing problems

Static Routing Problem

1

2

34P

P

P

P

MPLS offers static routing only!

MPLS not for QoS (contd.)

Internet is a significant and rapidly growing carrier of voice traffic

Ineffective and impractical for fluctuating demands of VoIP

MPLS nothing but domain-specific circuit switching

MPLS for VPNs

No automatic encryption of data Susceptible to data leak if a connection is

disrupted Potential for administrator doing wrong

provisioning causing loss of privacy Not clear how MPLS will make use of

encryption for security ISPs must manage routing table for each VPN

Where does MPLS fit ??

Aims to perform a useful function at the wrong layer – not universally useful

LSR, according to IETF specs, expects to speak IP

No strategy for evolving an existing ATM network into MPLS network

No Application-level Routing Intelligence

Need to distinguish different packets on the network

QoS requirements statically determined in MPLS

Can’t make use of application specific knowledge and requirements

MPLS unfit for VoIP

MPLS unaware of application requirements No alternate routing to prevent latency, delay,

packet loss, jitter Static and domain-specificity hurts in long run

Conclusions

MPLS static and non-application aware Suited to core of major networks Can be deployed only in single-domain

environment where all routers are MPLS enabled

No end-to-end solution Guaranteed QoS still elusive

MPLS – No Magic, All Myth!!