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EL 9933 READINGS IN ELEC & COMP ENGR I
MULTI PACKET LABEL
SWITCHING[MPLS]
TECHNOLOGY
Guided by:
Prof. Eric Brendel
APURV BHATAWDEKAR
MS Telecommunications Network
ECE Department, Polytechnic Institute of NYU
SPRING 2011

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TOPICS
 MPLS Fundamentals – Why, Where, What & How?
 MPLS Components – Label and Label Stack
 MPLS Operation – Label Operations & Forwarding,
label spaces and distribution modes.
 MPLS Applications - Overview
 MPLS VPN Model – Topology based
 MPLS TE – Topology based
 MPLS AToM – Topology based
 MPLS Future Scope - Overview

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WHY a choice for Telecom Network ?
• Handle a variety of Services, both legacy & new
over a single network.
• Build once, Sell many policy.
Which all Industry?
• Retailers
• Investment Companies
• Government Agencies & the Military
• Health Care Organizations
• Technology Enterprises

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About MPLS technology
 Packet forwarding is done based on labels
 Labels assigned when the packet enters the network
 Labels inserted between layer 2 and layer 3 headers
 MPLS nodes forward packets based on the label
 Separates ROUTING from FORWARDING
 Routing uses IP addresses
 Forwarding uses Labels
 Labels can be stacked

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MPLS COMPONENTS
CE PE CE PE CE
C Network P Network C Network
(Customer Control) (Provider Control) (Customer Control)

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MPLS Labels and Label Stack
Layer 3 Network Layer
Layer 2.5 MPLS Header
Layer 2 Data Link Layer
Various Label LABEL EXP S TTL
Encapsulation
20 3 1 8
techniques
1
2
6

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LABEL OPERATIONS
• PUSH : Add a label
• SWAP : Map in label to out label
•POP : Remove a label

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LABEL OPERATIONS (Cont…)
• Penultimate Hop Popping (PHP)
Implicit Null – Label 3

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MPLS Label Space
Per-Interface Label
Space
-the packet is not forwarded
solely based on the label, but
based on both the incoming
interface and the label.
Per-Platform Label
Space
-the label is not unique per
interface, but over the LSR
assigning the label

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MPLS Label Distribution Modes
Label distribution mode DoD mode
UD mode
LLR mode
Label retention mode
CLR mode
Independent mode
LSP control mode Ordered mode

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5. Edge LSR at
MPLS Egress Removes
Label and Delivers
OPERATIONS Packet
1. Existing Routing
Protocols (e.g. OSPF, IS-IS) B
Establish Reachability to
Destination Networks
4. LSR Switches Packets
Using Label Swapping
A
2. Label Distribution Protocol (LDP)
Establishes Label to Destination
Network Mappings C
3. Ingress Edge LSR Receives Packet,
Performs Layer 3 Value-Added
Services, and “Labels” Packets

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MPLS Applications
Traffic engineering The ability to FORWARD on
and STACK LABELS allows
•Force traffic along predetermined pathsprovide some useful
MPLS to
features
MPLS VPN
•Layer 3 – Provider has knowledge of customer
routing
•Layer 2 – Provider has no knowledge of customer
routing
Any Transport over MPLS

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Virtual Private Networks
Technology
What is VPN ???
A Virtual Private Network (VPN) is a private network constructed
within a public network infrastructure, such as the global Internet.
A VPN connects the components and resources of one network over
another network.
Usually, this is done by a combination of tunneling, encryption,
authentication, and access control technologies and services used to
carry traffic over the Internet, a managed IP network or a provider's
backbone.

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VPN MODEL TYPES
The Overlay model The Peer model
• Both provider and customer network
• Private trunks over a TELCO/SP use same network protocol and
shared infrastructure control plane.
- Leased/Dialup lines
- FR/ATM circuits • CE and PE routers have routing
adjacency at each site.
- IP (GRE) tunneling.
• All provider routers hold the full
• Transparency between provider routing information about all
and customer networks. customer networks.
• Optimal routing requires full • Private addresses are not allowed.
mesh over Backbone.
• May use the virtual router capability

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MPLS VPN – Layer 3
 Private, connectionless IP VPNs
 Outstanding scalability
 Customer IP addressing freedom
Secure support for intranets and
extranets
 Easy to provide
Intranet/Extranet/3rd Party ASP
Support over any access or
backbone technology

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Peer to Peer VPN Model

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Building Blocks of VPN
VRF
Route distinguisher (RD)
Route targets (RT)
Route propagation through MP-BGP
Forwarding of labeled packets

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Forwarding Plane
L2 Header Label 1 Label 2 L3 Header Data
Site 2
CE
CE PE
Site 1
PE P
P

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Any Transport over MPLS
• Need: ATM and Frame Relay traffic still present
• Commonly known scheme for building layer 2 circuits over
MPLS
• Attachment circuit—layer 2 circuit between PE and CE
• Emulated circuit—pseudowire between PEs
PSN Tunnel
Pseudowire 1
Pseudowire n

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AToM Architecture

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WHY : Traffic Engineering ?
MPLS TE is a solution for this problem in the following ways:
 Provides efficient spreading of traffic
 Takes into account the configured bandwidth of links.
 Takes link attributes into account.
 Adapts automatically to changing bandwidth & link attributes.
 Source-based routing is applied to the traffic-engineered load as
opposed to IP destination based routing.

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Building Blocks of MPLS TE
Link
 TE information distribution
 An algorithm to calculate the best path from the head end LSR to the tail
end LSR
 A signaling protocol to signal the TE tunnel across the network
 A way to forward traffic onto the TE tunnel

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Tunnel Terminology, Attributes &
Path Selection
Head End Tail End
Tunnel Attributes Tunnel has two path options
– Bandwidth -- Dynamic
– Priority -- Explicit
– Metric selection ( TE vs. IGP metric)
– Affinity

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Forwarding Traffic onto MPLS
TE Tunnels
Static routing
 Policy-based routing
 Autoroute announce
 Forwarding adjacency
 Direct mapping of AToM traffic onto TE tunnels
Class-based tunnel selection

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Future Developments in MPLS
MPLS Control Word
FCS Retention
Circuit Emulation
GMPLS
OAM Protocols – BFD , LSR Self Test
MPLS Labeled Multicast

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References
1. www.cisco.com
2. MPLS Fundamentals by Luc De Ghein, CCIE No. 1897

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Thank You