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Copyright 2005 OPNET Technologies, Inc. Confidential, not for distribution to third parties.

Introduction to MPLS

Technology Tutorials

Session 1801

Copyright 2005 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 2

1801 Introduction to MPLS

Agenda

Introduction

MPLS Fundamentals

MPLS Applications

Traffic Engineering

Resiliency and restoration

MPLS-based VPNs

Advanced Topics

MPLS Support in OPNET

Conclusion

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What is MPLS?

Different things to different people

One answer

Generic tunneling mechanism

Evolving suite of IETF standard/near standard protocols for the Internetbackbone

Enabling technology for new and converged IP services

Integrates packet switching with network layer routing

De-couples routing from forwarding in an IP network

Works with any routing paradigm

Employs a simple forwarding paradigm called label swapping



Origins

Mid 90s

Switch when you can, route when you must

Bring L2 performance to L3 (IP)

Switching (L2)

Simple table lookup

Could be done in hardware at wire speed

IP Routing (L3)

Longest prefix match algorithm

Was performed in software at < wire speed

Make IP networks work more like ATM without the cost andcomplexity

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MPLS Timeline

Precursors started in mid 1990s

Toshiba (Cell Switching Router)

Ipsilon (IP Switching)

Cisco (Tag Switching)

IBM (Aggregate Route-based IP Switching)

IETF MPLS working group formed in 1997 MPLS was chosen as a generic name for the technology

MPLS RFCs released in 2001



MPLS Combines Routing and Switching

IP routing (pure Layer 3 technology) Provides rich functionality: wide range of protocols, interface types, and

speeds

ATM switching (pure Layer 2 technology) Does simple forwarding of Layer 2 protocol packets based on circuit numbers

One view is that MPLS combines the best of both Rich functionality and flexibility of Layer 3 routing

Speed and simplicity of Layer 2 switching

IP Routing ATM SwitchingMultiprotocol Label

Switching

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Motivation for MPLS Today

Original performance motivations no longer relevant LPM can be done at wire speed

Other factors have taken over Growth and evolution of the Internet

Growing number of users

Increasing need for bandwidth

Diverse service types and QoS requirements

Use of overlapping address space (RFC 1918)

Managing bandwidth vs. buying bandwidth

Limitations of existing core technologies

Movement to a single unified network

Need for scalability in the Internet backbone



Agenda

Introduction

MPLS Fundamentals

MPLS Applications

Traffic Engineering


MPLS-based VPNs

Advanced Topics


Conclusion

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MPLS Fundamentals

How it works

The Label Switched Path (LSP)

Label Switching Router (LSR) functions

Traffic assignment

Inside the MPLS label



Label Switching Router (LSR)

Sets up Label Switched Paths (LSPs)

Forwards traffic along LSPs using label swapping

Can be a router or switch

Runs one or more IP routing protocols

to learn network topology

to distribute MPLS topology state information to other LSRs

to forward native IP packets

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Label Switched Path (LSP)

A unidirectional tunnel through the MPLS domain For a round trip, two LSPs are required



Forwarding Equivalence Class (FEC)

Definition: A group of IP packets that are forwarded in the same way

Packets are classified into FECs

Only once

At the ingress to the MPLS domain

A FEC identifies a set of IP packets to map to an LSP

Packets in the same FEC

Receive the same label from the ingress LSR

Are mapped to the same LSP and forwarded over the same path (or sets ofpaths in the case of multi-path routing)

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FEC (cont.)

FECs are not necessarily new In conventional IP, a FEC is formed at each routerbased on Layer 3 lookup

Packets with the same longest matching address prefix (based on destinationaddress) are treated in the same way

FECs are currently derived from IP routing protocols

Based on destination IP prefix (IP header)

Mappings can be policy-based (e.g., ToS bits)

MPLS offers additional flexibility and granularity for classification ofFECs, such as

Same egress router or switch

Same longest matching destination address IP prefix

Same longest matching destination IP Prefix AND same Type of Service bits Same application flow



MPLS How It Works

LSRs use (extended) link state IGPs to learn network topology

Path setup: For each LSP configured on an ingress LSR:

Ingress LSR looks up or calculates the path

Ingress LSR signals the LSP

Transit and egress LSRs set up labels for the LSP and confirm to ingress LSR

Forwarding: For each packet that arrives on an ingress LSR:

Ingress LSRs assigns traffic to LSPs based on FEC

Interior LSRs forward traffic using label switching

Egress LSR forwards traffic based on IP or VPN rules

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MPLS Domain Boundaries

IP packet enters the MPLS domain

Ingress LSR (LSR1) assigns a label and forwards the packet to the next hop in the

label switched path (LSP) Intermediate LSR (LSR2, LSR3) does a simple lookup, swaps the label, and forwards

the packet

Egress LSR (LSR4) or Penultimate hop (LS3) removes the label and forwards thepacket using based on conventional IP or VPN rules



Path Setup Example

LSR1 transmits a Label Request message to LSR4 Each downstream router modifies the route list

LSR4 transmits a Label Mapping message to LSR1 LSR4 assigns an inbound label and transmits upstream

Intermediate LSRs (LSR3 and LSR2) Store outbound label provided by downstream LSR

Assign an inbound label and transmit upstream

LSR1 binds the label to the FEC

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Packet Forwarding Example

Ingress: LSR1

Egress: LSR 4



MPLS Label

Short fixed length identifier used to designate a FEC

Has local significance only

Changes from hop to hop

For IP, the label is contained in a shim header

For ATM the label is VPI/VCI

For Frame Relay the label is DLCI

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MPLS Packet Format and Shim Header

MPLS is often described as introducing a shim header between theoriginal layer 2 and layer 3 headers

This is the reason MPLS is sometimes described as Layer 2.5

The 32-bit MPLS shim header is added to the IP header

Maps network layer routing to data link layer switched paths



Where Does MPLS Fit in the OSI Model?

MPLS works with and supports Layer 3 technologies, but does nothave routing and addressing

MPLS is not Layer 3

MPLS is not Layer 2

MPLS is Layer 2.5 Shim Layer

It helps Layer 2 and Layer 3 fit better

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Label Stacking

Labels can be ordered hierarchically in a stack

Label stacks permit nesting of LSPs

Similar to ATM VPs for aggregating multiple VCs, but MPLS supportsarbitrary levels of hierarchy

Can be used to reduce the number of LSPs through the core

Only top label is swapped

Packets are forwarded based on the value of the label at the top of the stack

Last-in, first-out stack



Label Stacking Example

Useful for IP/MPLS VPNs and TE (illustrated later)

Also used to support resiliency (FRR bypass tunnels)

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MPLS Routing

Topology Determination

Path Determination

IGP

CSPF

Explicit Routing

IP Routing Interactions

Load Balancing



Topology Determination

Definition: An MPLS domain is a set of physically connected LSRs(includes LSRs acting as LERs)

Routers within an MPLS domain use routing protocols to discover thenetwork topology

MPLS IGPs: OSPF-TE and ISIS-TE

MPLS EGP: BGP4

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LSP Path Determination

Path determination options depending on label distribution protocol

LSP paths can be determined using

LDP: Routers calculate dynamically using IGP

Selects IGP shortest path

RSVP-TE: Routers calculate dynamically using CSPF

Selects shortest path that meets constraints

RSVP-TE: Network operator specifies using Explicit Routes (ERs)

Uses configured ERs

Multiple Explicit Routes can be configured per LSP

Primary (no more than one)

Secondary (zero or more)



LSP Attributes

Path Definition Defined at ingress LSR

Remote destination (usually loopback address)

Path Selection and Management Administratively configured explicit routes

Explicit routes may be mandatory

Fallback to CSPF

CSPF constraints, including:

Required bandwidth

Maximum hop count

Resource classes: eligibility to use a link Must be consistent with resource classes configured on interface

Priority (Setup and Holding) Used for preemption (policy-based bumping) in dynamic routing

Resilience Mode (Recovery policy)

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Constraint-Based Shortest Path First(CSPF)

Automated constraint-based TE is its intent Associate flow requirements with a FEC

Track new link state parameters

TE Extensions to OSPF and IS-IS

Calculate the shortest path across the MPLS domain that

Meets the flow requirement based on current network state

Meets a set of constraints specified in LSP attributes

Path cost based on Dijkstras shortest path first (SPF) algorithm Build a network graph

Graph edge (link) cost: inherit or override IGP link cost

Apply constraints: prune a link if

Insufficient resources to accommodate the LSP

Link cannot satisfy LSP local constraints (e.g. resource classes) Compute shortest (least-cost) path using the pruned graph

Path must also satisfy LSP constraints (e.g. maximum hops)



Explicit Routing

Explicitly routed LSPs

Sometimes referred to as Traffic Engineered Tunnels

Administratively pinning routes of LSPs

Done manually or automatically (e.g., using a TE computation)

Can mix and match with dynamically routed LSPs

Local (selected LSPs, partial mesh) a.k.a. Tactical

Global (full mesh among LERs)

Permits centralized, global decision making for traffic engineering

Explicit Routes are the output (decision variables) of TE

Indirectly enables QoS- and service-level-focused mechanisms Assuring that certain traffic or service types traverse certain network resources

(devices, links)

Possibly computed using external TE solution

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Explicitly Routed LSPs

Explicit routes can be strictly or loosely defined Strict: All hops are specified from ingress to egress, that is, each next hop is

directly connected (fully pinned)

Loose: The path between ingress and egress is partially specified (partiallypinned). When the next hop is not directly connected, use IGP or CSPF toreach it.



Agenda

Introduction

MPLS Fundamentals

MPLS Applications

Traffic Engineering


MPLS-based VPNs

Advanced Topics


Conclusion

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Traffic Engineering

Top-level view Capacity Planning: placing bandwidth to support traffic

Traffic Engineering: placing traffic where there is bandwidth

MPLS ability to arbitrarily segregate flows at whatever level ofgranularity is desired and to route those flows independently of oneanother (regardless of source/destination addresses) forms the basis fortraffic engineering



MPLS Traffic Engineering

MPLS traffic engineering defined

Definition

Controlling traffic in a predictable manner to maintain service levels

Goal

Optimize network resource utilization and traffic performance

Three types

Inline TE performed on a device using local information

Online TE done using global information by a central serverconnected to the network

Offline TE done by a server external to the network usingglobal information

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Why TE?

Bandwidth availability Infrastructure limitations, lead times

Pipe size granularity issues

Class-of-service routing

Knobs to tweak under failure scenarios

Hedge against traffic issues

Uncertainty, growth, fluctuations

Economics

Especially today



Traditional IP TE Motivation

Problem: Hyper-aggregation of flows

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Traditional IP TE Cycle

ClassicallyUnstable

Still flawed, but lessso with predictive

tools

Solution approach: Trial and Error



The Problem with Traditional IP TE

Brute force solution

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TE with MPLS

MPLS Tactical LSP Solution



MPLS Traffic Engineering

Online/Offline

MPLS provides the building blocks to perform IP traffic engineeringbetter, but it does not provide the full TE solution

TE presents an opportunity to solve some global optimizationproblems focused on balancing loads and improving service levels

This requires new TE software, methodology, and processes

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MPLS Online/Offline TE Process



MPLS TE Automated Model-Building

Automatically constructing a detailed, operationally correct model ofthe existing network

Topology (nodes and links)

Detailed device and protocol configuration

Existing LSPs, their configuration, routes

Link and LSP usage information

IF-MIB (Cisco), IF-MIB extension (Juniper)

(Optionally) traffic

Usual imperfect sources

3rd party systems

TMS (Cisco)

Traffic inference

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MPLS TE Explicit Route Generation

Automated design and analysis of traffic engineering solutions againstoperational goals

Design

CSPF versus explicit routing

Explicit route computations (primary, secondary, restoration, etc.)

Analysis

Performance analysis (e.g., design utilization metrics, device and linkusage/subscription metrics, delay metrics, etc.)

Failure analysis

Traffic growth analysis

Topology analysis



Global LSP Optimization vs. Greedy LSP

Routing

Greedy: Ingress router uses the constrained shortest path at LSP setup time

The setup order can greatly affect the overall solution quality

Global optimization: use a holistic view to generate a globally optimal solution

Example: Largest LSP (size 8) takes its shortest path, other LSPs are blocked

8

12

8

6

6 - blocked

Routed second

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MPLS TE Validation

Supports network operations in understanding and using expertjudgment about the final changes to be implemented

Must be supported on two levels:

Summary reports on MPLS configuration adds, deletes, or changes and theirimpact on design criteria and operational tolerances

Ability to directly review and diff configurations for the affected devices

Validation concerns include:

Correctness

Value of changes

Ensuring that decisions were based on accurate and current data



MPLS TE Deployment

Ability to parse the validated configuration results generated by thesystem into a form most useful for implementation

Issues here are:

Deployment model (matter of operations preference)

Granularity, order, chunking

Deployment means

Direct through device configlets, SNMP, NMS/OSS interfaces

Requires Change Management functions consistent with deploymentmodel and means

Ability to introduce, check point, archive, and back out configuration changes

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MPLS TE Automating the Process

The answer to What is the appropriate time scale for this cycle?drives automation

Closer to being a reality in the technology than one that will beaccepted organizationally

IP/Optical and other NGN initiatives may contribute to accelerating thetechnology and increasing its acceptance

Expect a gradual transition through

Human operated

At each process step

Human supervised

For validation and to supervise deployment

Exception managed Operated like IGPs are today



MPLS TE Results on an Example Network

Basic MPLS TE load balancingvia primary ERs improves networkperformance

Survivable TE assures networkfailure resilience

Note: Results are network-specific.

96%

41%

39%

0%

20%

40%

60%

80%

100%

CSPF TE

Maximum Link Utilization

Failure

Normal

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Summary: TE Options

Inline (CSPF)+ Still better than IGP routing

+ Least overall complexity

+ No need for external TE system

- Non-optimal use of bandwidth

- Still need process or mechanism to sizeLSPs

- Vendor interoperability issues?

Online/Offline TE (ERs)+ Most efficient use of bandwidth

+ Better protection (SRGs)

- Can be operationally complex



MPLS TE Deployment Considerations

Governed by underlying topology, traffic mix and applications

MPLS topology different deployment models for LSP topology(flat/hierarchical)

Flow segregation different strategies for flow segregation onto LSPs (FECs)

Application-specific deployment to support specific applications or services(QoS/ToS per-hop behaviors)

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MPLS Topology For Traffic Engineering

For TE purposes, MPLS is deployed in the core routers (or aTE layer internal to the core routers)

Deployment scenarios include

Tactical deployment to fix a particular problem

Alleviate congestion

Improve service level(s)

Fully traffic-engineered flows

Motivated by measurement it enables and control

Full-mesh or hierarchical



MPLS Topology For Tactical TE

To alleviate congestion, an LSP is created to move one of theflows on the congested link to an alternate (non-IGP) route

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MPLS Topology A Full TE Mesh

Enables measurement octet/packet counts on each LSP

Enables control routing decisions per LSP if needed

Flat Deployment Hierarchical Deployment



Intermission

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Agenda

Introduction

MPLS Fundamentals

MPLS Applications

Traffic Engineering


MPLS-based VPNs

Advanced Topics


Conclusion



MPLS Resiliency and Restoration

An LSP becomes unusable if any network resource along its route fails

LSP restoration mechanisms can be setup at different time scales

Mechanisms generally have a tradeoff between the time required to restoreservice after a failure, resources used, and complexity of configuration

Slower mechanisms tend to provide better long-term solutions in terms ofnetwork resources

Faster mechanisms protect in-flight data but at the cost of sub-optimal use ofnetwork resources

Some carriers seeking near SONET (50 milliseconds) restoration times

Multiple mechanisms make sense

A networks resiliency is the degree to which the network cansuccessfully survive failures

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Resiliency and Restoration

Can occur at one or several layers Optical layer

SONET layer

MPLS layer

IP layer

Routing protocol convergence

Configuring restoration mechanisms at all layers can be expensive

Need to balance cost and complexity of planning for resiliency withcost and risk of a failure.



Types of Failures

Link Failures

Node Failures

Shared Risk Group (SRG) Failures

SRGs are collections of network resources that share the same risk offailure.

Examples:

Circuits that traverse that same physical fiber span (fiber cut)

Devices in the same building (natural disaster)

Devices sharing the same power supply (power failure)

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MPLS Restoration Two Common Means

Path protection Head end can reroute what it signaled

Longer-term, more optimized, repair made at the source

Motivation is quality of repair at a cost of speed ~ O(seconds)

(Alternative strategy: have an alternate LSP up and running whose usage undernormal conditions is precluded using metrics)

Local protection

Temporary, likely sub-optimal, repair made locally in the neighborhood of thepoint of failure to keep critical flows up

Motivation is speed ~ O(milliseconds)

Attempt to keep data in flight until more permanent repair can be made

Example: Fast Reroute

Path and local protection are complementary

One is a short term fix, the other a long(er) term fix



Path Protection

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Link Protection (Local)



Node Protection (Local)

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SRG Protection (Local)

Protected SRG



MPLS Protection Approaches

Path protection

Failover to CSPF route

Default

Requires head-end router to detect failure, recompute shortest path on the remainingnetwork, and set up new path (may be several seconds)

Failover to precomputed secondary route

Requires head-end router to detect failure and set up new path

The secondary route should be failure disjoint from the primary

Secondary route only uses resources when the primary fails

Failover to backup (standby) LSP

For each primary LSP, one or more backup LSPs are designated

Backup LSPs are set up before failures occur and can consume resources under non-failure conditions

Can be set up with zero bandwidth

TE metric used to prevent use of the backup LSP under non-failure conditions

Head-end router switches from primary to backup when it detects the failure

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MPLS Protection Approaches

Local protection Each LSR in the path has a precomputed alternate next-hop LSP to replace thephysical next hop if the primary becomes unavailable (Cisco Fast Reroute)

Requires stackable LSPs (LSPs riding other LSPs)

Does not require head-end signaling (45-50 milliseconds typical)

Does not use additional resources until the failure occurs

Temporary solution until head-end router can restore the LSP

Physical layer protection

Relying on the SONET redundancy features to handle link failures before theyare detected by IP/MPLS (< 50 milliseconds)

Hybrid strategies

Example protection strategy:

Platinum/Real-time traffic (VoIP/Video): FRR

Gold/Premium: secondary explicit routes

Bronze/Best effort: no protection



Agenda

Introduction

MPLS Fundamentals

MPLS Applications

Traffic Engineering


MPLS-based VPNs

Advanced Topics


Conclusion

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MPLS-Enabled IP VPNs

Head-to-head with MPLS TE in importance

MPLS VPNs (Virtual Private Networks) are inherently based onMPLS ability to segregate flows in this case on a per VPN (i.e. percustomer) basis from provider edge (PE) to provider edge (PE)

Key motivators (analogous to FR/ATM) for MPLS VPNs

Revenue

Address space reuse and overall ease of management, security, etc.

Ability to address customer service levels (via routing or in combination withQoS mechanisms) and monitor customer traffic

Granularity of decisions available under failure conditions



MPLS-Based VPNs

Motivation for MPLS VPNs

MPLS-Based Layer 2 VPNs


Tradeoffs MPLS-Based Layer 2 versus Layer 3 VPNs

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Motivation for MPLS L2 VPNs

Have a single network technology for all types of services PE-to-PEregardless of the customer-facing technology (decouple PE technologyfrom CE technology)

One operations center, reduced staff, one OSS/BSS infrastructure

A single MPLS infrastructure enables traditional (FR, ATM) and new(Ethernet) VPN services over a single Packet-over-SONET (POS)infrastructure

Network consolidation for SPs offering private data and IP services

New revenue opportunity for IP services only providers

Simplify provisioning

Signaling and label stacking

Touch only edge devicesScalability

Core switches aggregate MPLS tunnels (label stacked) and thus managesfewer connections




Martini MPLS Layer 2 VPNs

Encapsulations for Frame Relay, Ethernet port /802.1q VLAN, ATM AAL5,ATM Cells, and PPP/HDLC

Provider pre-provisions outer (service-related) LSPs all services look like avirtual circuit to the MPLS network

Each service is provisioned over MPLS using LDP signaling by associatingeach endpoint with common VC identifier (VCID)

e.g., for FR, the port/DLCI at each end is associated with the same VCID

Network automatically determines VC Label to push onto the layer 2 frame

LDP sessions advertise VC Labels for VCIDs

Network also determines Tunnel Label to stack on top based on usual routing

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Martini MPLS Layer 2 VPNs



Example L2 VPN Frame Relay

FR from customer premises (e.g., FRAD) to edge LSR

Edge LSR

Translates FR DLCIs

Maintains VC Label to in/out port and DLCI mappings

MPLS defines the label distribution and encapsulation

FR PDU (including header, FECN and BECN bits, ) transported intheir entirety edge to edge

FR DE bit mapped to MPLS EXP values

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Example L2 VPN ATM

ATM from customer premises (e.g., ATM Switch) to edge LSR

Edge LSR

Translates ATM VPI/VCIs

Maintains VC label to in/out port and VPI/VCI mappings


AAL5 and ATM cell transport modes are supported

AAL5 mode reassembles ATM PDUs from a VC into a packet

Cell mode transports each ATM cell as a packet

CLP bit to EXP field mapping supported



Example L2 VPN Ethernet

Ethernet/FastEthernet/GigabitEthernet from customer premises (e.g.,Ethernet Switch) to edge LSR

Edge LSR

Translates MAC addresses

Maintains MAC label to in/out port and optionally VLAN mappings


Ethernet frame is transported

VLAN tags are transported

Priority to EXP field mapping

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Kompella MPLS Layer 2 VPNs

Similarities with Martini VPNs Similar approach to label stacking for scalability

Similar applications (ATM, FR, Metro Ethernet)

Differences

VPN membership information distributed automatically via BGP

VPN sites can be added with little provisioning

BGP permits Service Provider to inter-work unlike media (e.g., ATM and FR)in a scalable fashion over MPLS

Extended service offerings



VPLS (Virtual Private LAN Services)

Martini VPNs only provide point-to-point connectivity

VPLS builds upon Martini to provide multipoint connectivity

Alternative to L3 MPLS VPNs

Ethernet based (Virtual LAN) Per-customer broadcast domain

Full mesh of Martini tunnels between PE devices

PE devices learn MAC forwarding information just like regular Ethernetswitch

Frames with unknown MAC addresses are broadcast

Full mesh and broadcast nature of Ethernet creates scalability issues Hierarchical-VPLS (H-VPLS) addresses these limitations

2 tier architecture

Draft-ietf-l2vpn-vpls-ldp-01.txt

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Mature technology based on BGP/MPLS VPNs RFC2547

Services enabled

IP VPNs to enterprise customers

Inter-provider VPNs hook two VPNs together across providers

Carrier-of-carrier services

IP transport to retail ISPs BGP/MPLS VPN across carrier core only

IP transport to SP itself providing L2/L3 services BGP/MPLS VPN acrossthe network of SP and carrier

Mature technology

Large-scale deployments

Hardware optimized for scalability in excess of 1000 VPNs per PE

Mature provisioning/management software



MPLS Topology for MPLS BGP VPNs

VPNs with MPLS and BGP Internet Draft draft-rosen-rfc2547bis-03.txt (Feb 2001)

Three device roles are defined CE (customer edge) Router

PE (provider edge) LSR

P (provider core) LSR

PE device:multiple virtual routing/forwarding (VRF) tables One forwarding table per set of directly attached sites with common VPN

membership

Customer routes are extended with unique label (Route Distinguisher)

Permits private addressing

Multiprotocol BGP (MBGP) extensions advertise VPN reachability

PE LSRs participate in a full mesh of MBGP that distributes VPN labels

LDP typically used to distribute path labels from PE-to-PE routers Uses MPLS hop-by-hop routing along IGP path

P routers do not need to be aware of VPN routes

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PE

CE

IP

1) Receive IP and

send IP datagram

to PE via ATM, FR,

Ethernet, etc.

IP 2547 L2 MPLSMPLS L1

2) Add RFC 2547

Header Label for

VPN ID.

Add MPLS tunnel;

label and send to

MPLS network.

RFC 2547: Forwarding Plane



CE

PE

CE

IP

3) Pop MPLS tunnel

label.

4) Pop VPN label and

send to CE.

IP 2547 L2 MPLSMPLS L1

RFC 2547: Forwarding Plane

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CE 1

PE 1P

1) CE1 PE 1

Exchange routers

with IGP (Rip, OSPF,IS-IS)

192.168.10.0/24.

2) PE 1 build VRF for

VRF BLUE 192.168.10.0/24.

VRF Blue

RFC 2547: Control Plane



CE 1

PE 1

PE 2

CE 2

AB

4) PE 2 build VRF Blue VPN

for 192.168.10.0/24.

VRF Blue

P

3) PE1 PE 2

Exchange routes for Blue VPN

with BGP 192.168.10.0/24.

Do not share with P routers.

Use LDP tunnel or RSVP.

RFC 2547: Control Plane

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CE

CE

192.168.10.0/24 192.168.10.0/24

192.168.10.0/24192.168.10.0/24

Company B

Company A

VRF Blue

VRF Red

RFC-2547: Overlapping Private Addresses



CE

CE

192.168.10.0/24 192.168.10.0/24

192.168.10.0/24192.168.10.0/24

Company B

BGP

RD 1 (blue)

RFC-2547: Overlapping Private Addresses

192.168.10.0/24

RD 2 (red) 192.168.10.0/24

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MPLS L2 VPNs Versus L3 VPNs

L2 VPNs (Martini/Kompella/VPLS)

Positives: Traditional L2 VPN from customersperspective

Provider not routing customer traffic

Single network architecture andinfrastructure for both Internet and VPNtraffic

Decouples core and edge technologies

Auto-provisioning via LDP setup

Negatives: Point-to-point focus

(Martini/Kompella)

Scalability (VPLS)

Not as flexible in terms of serviceopportunities

L3 VPNs (RFC2547)

Positives: Value-added service for customers that

want to outsource

Mature technology

Lots of (somewhat esoteric) serviceopportunities QoS/CoS, carrier ofcarriers, inter-SP VPNs

Negatives:Not transparent - migration requires

effort

Customer must peer with provider

CE device must be a router

Some customers strongly object to thisinvasion of privacy



Agenda

Introduction

MPLS Fundamentals

MPLS Applications

Traffic Engineering


MPLS-based VPNs

Advanced Topics


Conclusion

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Advanced Topics

Implementing QoS in MPLS


IGP Interactions

Load Balancing

Status of MPLS

Whos working on MPLS




Multiple service levels (e.g., Bronze, Gold, Platinum)

Service Level assignment based on VPN (ingress port) or ToS (IPheader)

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Implementing QoS in MPLS LSP-based

Strategy 1: Apply QoS to LSP Multiple LSPs between each ingress/egress LER (full mesh per service level!)

Destination IP address & ToS, or VPN, used in FEC

L-LSP

LSPs differentiated by

Setup/Hold Priorities (for dynamic/CSPF routing)

Primary Explicit Routes (favoring some LSPs in global optimization)

Protection mechanisms (Fast Reroute, Secondary Explicit Routes)

Resource classes (to reserve shortest paths for best service)




IPQoS-based

Strategy 2: Piggyback underlying IP QoS

Single LSP between each ingress/egress LER

Destination address (only) used in FEC

E-LSP

Use ToS to assign EXP bits in MPLS Shim header

Configure transit LSRs to provide favorable queuing based on EXP bits

Must provide protection mechanisms (Fast Reroute, Secondary ERs) andadequate bandwidth (primary and protection) to all LSPs

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Implementing QoS in MPLS DiffServ TE

Strategy 3: DiffServ TE

OPNETWORK 1825Advanced Topics in MPLS: QoS, DiffServ TE, and GMPLS




In an operational network, routing can be configured in a number ofways so that flows are routed using LSPs

BGP ingress/egress mode

Flows entering the network at an AS boundary can have their BGP next hopset to point to an LSP

Mechanism used for L3 MPLS VPNs

IGP Shortcut LSP

Examples are Ciscos Autoroute and Juniper IGP Shortcuts

Visible at head-end LER only

After IGP routing has computed the shortest path tree, a post processing step

is used to replace IGP next hops with shortcut LSP paths Forwarding Adjacency LSPs

Directly used in the IGP shortest path computation as layer-3 adjacencies

More predictable and intuitive than shortcuts

Results in N2 adjacencies in an LSP mesh

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IGP Interactions

IGPs often support equal-weight split path routing at each hop alongthe IGP path to a destination

The number of splits per hop is small typically four, but it is configurable

The number of splits compounds geometrically hop-to-hop (4x4x4, )

This creates de-facto load balancing under the best of circumstances

Can also create congestion where the equal-weight paths (IGP link weights areconfigured) do not reflect the link capacities along the paths

MPLS deployment disables IGP split pathing

MPLS can be configured similarly to provide split path routing alongparallel LSPs

Splitting is proportional to LSP bandwidth

Splitting occurs only once at the ingress of the parallel LSPs



Load Balancing

There are two categories of load balancing in MPLS

Path selection

When multiple equal cost paths to egress are available, CSPF can use tiebreaking rules to select the one to use:

Random randomly select a path to use

Least-fill prefer the path with the largest minimum available bandwidthratio

Most-fill prefer the path with the smallest minimum availablebandwidth ratio

where available bandwidth ratio = (avail bw on link)/(max reservable bwon link)

Balancing traffic over multiple LSPs

Per-prefix (IP addr/netmask) keeps individual flows on one route

Per-packet can split individual flows over multiple LSPs in proportion tothe bandwidth of the LSPs

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Status of MPLS

Lots of excitement

Hundreds of deployments worldwide

Cisco reported >200 deployments in 2003

Almost all providers offing some form of MPLS VPN service

Most are doing TE within their core

Standardization work continues

RFCs, internet drafts

Interoperability labs

University of New Hampshire's InterOperability Lab

Isocore Internetworking Lab



Whos Working on MPLS?

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Agenda

Introduction

MPLS Fundamentals

MPLS Applications

Traffic Engineering


MPLS-based VPNs

Advanced Topics


Conclusion



OPNET Support for MPLS?

MPLS data collection

Routers, LSPs, configuration

LSP utilization

Cisco, Juniper, Foundry

MPLS modeling, simulation & optimization

CSPF (OSPF-TE, ISIS-TE), ERs

LDP, RSVP

QoS, Diffserv-TE

Failure analysis

Traffic engineering optimization

Resiliency design

MPLS VPNs

L2 (Martini, Kompella, VPLS) & L3 (RFC 2547)

Graphical provisioning wizard

Views to study logical VPN topology

Support for MPLS-related R&D

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Agenda

Introduction

MPLS Fundamentals

MPLS Applications

Traffic Engineering


MPLS-based VPNs

Advanced Topics


Conclusion



References

Books

MPLS Technologies and Applications (Bruce Davie and Yakov Rekhter,Morgan Kaufmann, 2000)

Advanced MPLS Design and Implementation (Vivek Alwayn, ciscopress.com,2002)

MPLS and VPN Architectures (Ivan Pepelnjak and Jim Guichard,ciscopress.com, 2001)

Many vendors have literature posted on their websites

RFC and Internet draft documents

http://www.ietf.org/html.charters/mpls-charter.html

MPLS Forum http://www.mplsforum.org

MPLS Resource Center

http://www.mplsrc.com

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Other MPLS-Related Sessions

Network Tutorials Track 1818 Introduction to VPNs

1825 Advanced Topics in MPLS: QoS, DiffServ TE, and GMPLS

Network Analysis, Planning and Troubleshooting

1331 Planning and Analyzing VPN Architectures

1310 Planning, Analyzing, and Optimizing MPLS TE and FRR Deployments

1354 Planning, Analyzing, and Optimizing DiffServ TE and MPLS QoS

Discrete Event Simulation for R&D

1511 Understanding MPLS Model Internals


Take-Away Points

Main Concepts

Separates control and data plane

Supports multiple routing paradigms

Simple forwarding paradigm (label swapping)

Enables advanced IP Services

Triple Play (Voice, Video, and Data) with QoS

Traffic Engineering


VPNs

Compatible with existing technologies ATM, Frame Relay, Ethernet

Broadly supported in OPNET products

Import: VNE Server and MVI

Simulation and design: SP Guru

Documents

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