MPLS and Traffic EngineeringDecember 08, 2003

MPLS and Traffic Engineering

Zartash Afzal UzmiDepartment of Computer Science

Lahore University of Management Sciences (LUMS)

MPLS and Traffic EngineeringDecember 08, 2003

Outline

Traditional IP Routing IP Routing Operation and Problems Motivation behind MPLS

MPLS Terminology and Operation MPLS Label, LSR and LSP, LFIB Vs FIB Transport of an IP packet over MPLS

Traffic Engineering [with MPLS] Nomenclature Requirements Examples

MPLS and Traffic EngineeringDecember 08, 2003

Traditional IP Routing

IP forwarding is done independently at every hop

IP forwarding decisions are made using: Destination IP address (in packet header!) Routing table (updated by routing algorithms!)

Each IP router runs its own instance of the routing algorithm

Each IP router makes its own forwarding decisions

MPLS and Traffic EngineeringDecember 08, 2003

How IP Routing Works?

Searching Longest Prefix Match in FIB (Too Slow)

MPLS and Traffic EngineeringDecember 08, 2003

Problems with IP Routing

IP lookup (longest prefix matching) was a major bottleneck in high performance routers

This was made worse by the fact that IP forwarding requires complex lookup operation at every hop along the path

MPLS and Traffic EngineeringDecember 08, 2003

Motivation behind MPLS

1. Avoid [slow] IP lookup

2. Provide traffic differentiation (QoS)Voice is really different from data!

3. Evolve routing functionalityControl was too closely tied to forwarding!

4. Simplify deployment of IPv6

MPLS and Traffic EngineeringDecember 08, 2003

MPLS Label

To avoid IP lookup MPLS packets carry extra information called “Label”

Packet forwarding decision is made using label-based lookups

Labels have local significance only!

IP DatagramLabel

MPLS and Traffic EngineeringDecember 08, 2003

Router that supports MPLS is known as label switching router (LSR)

Path which is followed by using labels is called label switched path (LSP)

LSR and LSP

MPLS and Traffic EngineeringDecember 08, 2003

LFIB Vs FIB

Labels are searched in LFIB whereas normal IP Routing uses FIB to search longest prefix match for a destination IP address

Why switching based on labels is faster? LFIB has fewer entries Routing table FIB has very large number of entries

In LFIB Label is an exact match In FIB IP is longest prefix match

MPLS and Traffic EngineeringDecember 08, 2003

Transport of IP over MPLS

Label Pushing:

MPLS and Traffic EngineeringDecember 08, 2003

Transport of IP over MPLS

Label Swapping:

MPLS and Traffic EngineeringDecember 08, 2003

Transport of IP over MPLS

Label Swapping:

MPLS and Traffic EngineeringDecember 08, 2003

Transport of IP over MPLS

Label Popping:

MPLS and Traffic EngineeringDecember 08, 2003

Transport of IP over MPLS

MPLS and Traffic EngineeringDecember 08, 2003

What is Traffic Engineering?

Performance optimization of operational networks optimizing resource utilization optimizing traffic performance reliable network operation

How is traffic engineered? measurement, modeling, characterization, and

control of Internet traffic Why?

high cost of network assets service differentiation

MPLS and Traffic EngineeringDecember 08, 2003

Hyperaggregation Problem

Routing Protocols Create A single "Shortest Path"

MPLS and Traffic EngineeringDecember 08, 2003

Hyperaggregation Problem

MPLS and Traffic EngineeringDecember 08, 2003

Nomenclature

Network Engineering Put the bandwidth where the traffic is! Physical cable deployment Virtual connection provisioning

Traffic Engineering Put the traffic where the bandwidth is! Optimization of routes Ability to “explicitly route” traffic

MPLS and Traffic EngineeringDecember 08, 2003

Traditional Traffic Engineering

1 1

1 2

A B

C

Traffic sent to A or B follows path with lowest metrics!

MPLS and Traffic EngineeringDecember 08, 2003

Traditional Traffic Engineering

Demerits of IGP-based traffic engineering Changing traffic metric causes ALL the traffic to

shift to the new path Can not shift traffic destined only for A or only

for B to the new path (through C) Result is under or over utilization of some links

1 4

1 2

A B

C

MPLS and Traffic EngineeringDecember 08, 2003

Traffic Engineering: IGP vs. MPLS

Traditional TE (IGP based) The ability to move traffic away from the

shortest path calculated by the IGP to a less congested path

MPLS TE Allows explicit routing and setup of LSPs Provides recovery mechanisms failure Enables Value added services

VPNs, SLAs, VoIP, etc.

MPLS and Traffic EngineeringDecember 08, 2003

MPLS TE: How we may do it?

MPLS and Traffic EngineeringDecember 08, 2003

MPLS TE: How we may do it? LSPs are set up by LSRs based on information

they learn from routing protocols (IGPs) This defeats the purpose!

If we were to use “shortest path”, IGP was okay

MPLS and Traffic EngineeringDecember 08, 2003

MPLS TE: How we actually do it?

MPLS TE Requires: Enhancements to routing protocols

OSPF-TE and ISIS-TE Enhancement to signaling protocols to

allow explicit constraint based routing RSVP-TE and CR-LDP

Constraint based routing Explicit route selection Recovery mechanisms defined

MPLS and Traffic EngineeringDecember 08, 2003

Signaling Mechanisms

RSVP-TE Extensions to RSVP for traffic engineering

BGP-4 Carrying label information in BGP-4

CR-LDP A label distribution protocol that distributes

labels determined based on constraint based routing

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RSVP-TE

Basic flow of LSP set-up using RSVP

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RSVP-TE PATH Message

PATH message is used to establish state and request label assignment

R1 transmits a PATH message addressed to R9

MPLS and Traffic EngineeringDecember 08, 2003

RSVP-TE RESV Message

RESV is used to distribute labels after reserving resources R9 transmits a RESV message, with label=3, to R8 R8 and R4 store “outbound” label and allocate an “inbound”

label. They also transmits RESV with inbound label to upstream LSR

R1 binds label to forwarding equivalence class (FEC)

MPLS and Traffic EngineeringDecember 08, 2003

Rerouting LSP Tunnels

When a more “optimal” route/path becomes available

When a failure of a resource occurs along a TE LSP

Make-before-break mechanism Adaptive, smooth rerouting and traffic

transfer before tearing down the old LSP Not disruptive to traffic

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Recovering LSP Tunnels

LSP Set-up

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Protection LSP set up

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Protection LSP

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References

RFC 2702 “Requirements for Traffic Engineering Over MPLS”

RFC 3031 “Multiprotocol Label Switching Architecture”

RFC 3272 “Overview and Principles of Internet Traffic Engineering”

RFC 3346 “Applicability Statement for Traffic Engineering with MPLS”

MPLS Forum (http://www.mplsforum.org)

MPLS and Traffic EngineeringDecember 08, 2003

Upstream and downstream LSR

172.68.10/24

LSR1 LSR2

Upstream Downstream

Data

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How MPLS Works

Ingress LSREgress LSR

Searching Longest Prefix Match in FIB (Too Slow)

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Label Distribution

171.68.32/24

LSR1LSR2

Use label 5 for destination 171.68.32/24

MPLS Data Packet

with label 5 travel

ALWAYS, Downstream to upstream label distribution

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Downstream Un-solicited

171.68.32/24

LSR1LSR2

Send label Without any Request

Upstream Upstream

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Downstream On Demand (DoD)

171.68.32/24

LSR1LSR2

Send label ONLY after receiving request

Request For label

Upstream Down Stream

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Ordered Label Distribution

Ingress LSREgress LSR

Label

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Unordered Label Distribution

Ingress LSREgress LSR

Label

Label

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Label Retention Modes

LSR1

Destination

Label

Label

?

1. Liberal Retention Mode

2. Conservative Retention Mode

MPLS and Traffic EngineeringDecember 08, 2003

Label Distribution ModesLabel distribution modes

Advertisement

Downstream-on-Demand

Downstream-Unsolicited

IndependentOrdered

Distribution

Retention

ConservativeLiberal

MPLS and Traffic EngineeringDecember 08, 2003

Hierarchical LSPIngress LSR for LSP3

LSP1

LSP2

LSP3

Ingress LSR for LSP1

Egress LSR for LSP1