MPLS

1

Multiprotocol Label Switching Uniting Routing
and Switching for Scalable, High Performance
Services
Part
2

Agenda

• Layering

• Internet Core Switching/Routing

• Motivations for MPLS

• MPLS Overview

• MPLS Applications

• Summary

Part
3
OSI Reference Model
4
TCP/IP Reference Model
TCP/IP
OSI
Application
7. Application
6. Presentation
Not Present
5. Session
Not Present
Transport
4. Transport
3. Internet
3. Network
2. Data Link
2. Data Link
1. Physical
1. Physical
5
TCP/IP Architecture Terms
Host A
Host B
Router
IP(L3)
IP (L3)
IP
ehr drv
atm drv
ATM (L2)
Ethernet (L2)
6
Service Provider Backbone
Remote Office
Main Office
POP
CORE (ATM)
POP
Remote Office
POP
Service Provider
POP Point of Presence
7
The Network Core

• mesh of interconnected routers
• the fundamental question how is data transferred
  through net?
• circuit switching dedicated circuit per call
  telephone net example ATM
• packet-switching data sent thru net in discrete
  chunks

8
Network Core Circuit Switching

• End-end resources reserved for call
• link bandwidth, switch capacity
• dedicated resources no sharing
• circuit-like (guaranteed) performance
• call setup required

9
Network Core Packet Switching

• each end-end data stream divided into packets
• user A, B packets share network resources
• each packet uses full link bandwidth
• resources used as needed,

• resource contention
• aggregate resource demand can exceed amount
  available
• congestion packets queue, wait for link use
• store and forward packets move one hop at a time
• transmit over link
• wait turn at next link

10
Packet-switched networks Over Circuit-switched
networks

• Goal move packets among routers from source to
  destination through high speed switching core
• datagram network
• destination address determines next hop
• routes may change during session
• analogy driving, asking directions
• virtual circuit network
• each packet carries tag (virtual circuit ID),
  tag determines next hop
• fixed path determined at call setup time, remains
  fixed thru call
• Example Application
• IP/ATM

11
ROUTE AT EDGE, SWITCH IN CORE
CORE (ATM)
POP
POP
IP
L2
IP
IP
L2
IP
L2
IP
IP Routing In the Edge
IP Routing In the Edge
LABEL SWITCHING In the Core
12
What is the Problem with Current
Packet-Switching/Circuit-Switching or IP/ATM?

• Scalability.
• Need full (n2) mesh of virtual-circuits for
  desired performance, or partial meshing for low
  cost.
• IP uses any size packets whereas ATM uses 53
  Byte-cells.
• More bandwidth not efficient and very expensive
• Geographically dispersed enterprise networks need
  to be connected for transparent and secure
  private IP interconnection.
• IP and circuit-switching (e.g., ATM) technology
  uses different addressing scheme
• Addition/deletion of new branch office is an
  administrative nightmare n virtual circuits
  need to added/deleted
• Each edge router has to be big, fat, and tunnel
  rich.

13
IP/ATM Topology
14
Solution MPLS

• Integrate best of Layer 2 and Layer 3
• Scalability
• Reduce operations costs
• Increase reliability
• Create new revenue from value added IP Services.
• Virtual Private Networks(VPN)
• Traffic Engineering

15
Key MPLS Capabilities
IP/ATM Integration
Traffic Engineering
VPNs
16
MPLS Topology
17
What is MPLS?

• It is simply a Layer 2 tunnel designed to
  interoperate with ANY layer 3 protocol,
  especially IP.
• Analogous to an ATM or Frame Relay PVC
• Low-overhead virtual circuits for IP
• IP packets are encapsulated in the ingress switch
  known as the Label Edge Router (LER)
• Labels change at each segment in a Label Switched
  Path (LSP)
• Label Switched Router (LSR) swaps incoming label
  with new outgoing label
• Labels have local significance

18
MPLS Header

• IP packet is encapsulated in MPLS header and
  sent down LSP
• IP packet is restored at end of LSP by egress
  router
• TTL is adjusted also

IP Packet
32-bit MPLS Header
19
MPLS Header
TTL
Label
CoS
S

• Label
• Class of service
• Stacking bit
• Time to live
• Decrement at each LSR, or
• Pass through unchanged

20
MPLS Operation
1a. Existing routing protocols (e.g. OSPF, ISIS)
establish reachability to destination networks
4. Label Edge Router at egress removes label and
delivers packet
1b. Label Distribution Protocol (LDP)
establishes label to destination network
mappings.
2. Ingress Label Edge Router receives packet,
performs Layer 3 value-added services, and
label packets
3. Label Switches switch label packets using
label swapping
21
How Does It Work?

• Four fundamental components
• Packet Forwarding
• Path signaling
• Path selection
• Mapping Forwarding Equivalence Class

22
Traditional IP Forwarding
47.1
1
IP 47.1.1.1
2
IP 47.1.1.1
1
3
2
IP 47.1.1.1
1
47.2
3
47.3
2
23
MPLS IP forwarding via Label Switched Path (LSP)
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
24
Label Switch Path Signaling
Seattle
Boston (Egress)
San Francisco (Ingress)
Miami
25
Label Switched Path Signaling

• Once path is established, signaling protocol
  assigns label numbers in reverse order from
  Boston to San Francisco
• Signaling protocol sets up path from San
  Francisco to Boston, reserving bandwidth along
  the way

Seattle
Boston (Egress)
0
1965
San Francisco (Ingress)
1026
Miami
26
Path SelectionExplicitly Routed LSP ER-LSP
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
27
MPLS Benefits
Benefits of MPLS
IP over ATM Integration

• Shared backbone for economies of scale
• Keep up with Internet growth
• Reduced complexity for lower operational cost
• Faster time to market for IP services gt more
  revenue

• Traffic eng. for lower trunk costs
• Hierarchical routing for improve reliability of
  core
• Shared IP/Frame backbone for economies of scale

Traffic Engineering

• New revenue opportunity for SPs
• Scalability for lower operational costs and
  faster rollout
• L2 privacy and performance for IP

VPNs
14
28
IP over ATM Integration
IP over ATM VCs
IP over MPLS

• ATM cloud invisible to Layer 3 Routing
• Full mesh of VCs within ATM cloud
• Many adjacencies between edge routers
• Topology change generates many route updates
• Routing algorithm made more complex

• ATM network visible to Layer 3 Routing
• Singe adjacency possible with edge router
• Hierarchical network design possible
• Reduces route update traffic and power needed to
  process them

MPLS eliminates the n-squared problem of IP
over ATM VCs
29
Traffic Engineering Example
BEFORE
Utilization increases by 10
100Mbps_at_100
100Mbps _at_90
SELECTED PATH BY TE
100Mbps _at_60
100Mbps_at_70
25Mbps _at_ 30
25Mbps _at_ 70
OSPF
D
100Mbps _at_ 50
TE
S
30
Virtual Private Networks

• 1 Physical Network Many Private Networks

The Physical Network Topology
PHYSICAL LOGICAL
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
VPN 1
VPN 4
VPN 2
VPN 3
31
VPN Example
Private View
Private View
Public View
Cust A 10.1.1 VPN 1
Cust A 10.2.1 VPN 1
Controlled Route Distribution
(15)10.1.1
(15)10.2.1
(15)10.3.1
Internet- Scale VPN
Cust A 10.3.1 VPN 1
(354)128.24.2
(354)128.24.1
Cust B 128.24.2 VPN 2
Forwarding Examples IN OUT (1)10.2.1 (1)10.1.1
(1)10.3.1 (2)128.24.2 (2)128.24.1
Cust B 128.24.1 VPN 2
32
Separate Route Tables and Private Addressing
MPLS
33
Summary

• MPLS Label provides
• Scalable IP routing
• Advanced IP services
• Internet scale VPNs
• MPLS Benefits
• Lower operations costs
• Keep up with Internet growth
• New revenue services
• Faster time to market

MPLS
IP
34
Questions?
35
Thank You

• Luis Marrero
• lmarrero_at_ccs.neu.edu