Multi-Protocol Label Switch (MPLS)

1
Multi-Protocol Label Switch (MPLS)
2
Outline

• Introduction
• MPLS Terminology
• MPLS Operation
• Label Encapsulation
• Label Distribution Protocol (LDP)
• Any Transport Service over MPLS
• MPLS Applications
• Traffic Engineering
• MPLS-based VPN
• MPLS and QoS
• Summary

3
Why MPLS?

• Growth and evolution of the Internet
• The need for network convergence to support both
  voice and data services on both carrier and
  enterprise networks
• The need for advanced and guaranteed service over
  the Internet
• The need of virtual circuit but without the
  complexity of provisioning and managing virtual
  circuits.
• PVC too much provisioning and management work
• SVC signaling too complex to support and
  trouble shoot
• The need for an efficient transport mechanism
• routing flexibility
• forwarding price/performance
• Can we forward IP packets? Answer MPLS

Performance and service of Layer-2 and
management of layer-3
4
Motivation for Carriers

• Network convergence
• Single network to support voice and data traffic
• Ease of network management
• to provision new services
• to support various Service Level Agreements (SLA)
• Ease of Traffic Engineering
• To reroute during node failures or network
  congestion

5
Motivation for Enterprises

• Network convergence
• Single network for voice and data
• A meshed topology (any-to-any) without the
  nightmare of cost and management
• Confusion with too many Frame Relay PVCs
• Quality of Service (QoS) for intranet
• Ease of bandwidth management
• Flexibility of bandwidth provisioning

6
MPLS History

• IP over ATM
• IP Switching by Ipsilon
• Cell Switching Router (CSR) by Toshiba
• Tag switching by Cisco
• Aggregate Route-based IP Switching (IBM)
• IETF MPLS
• http//www.ietf.org/html.charters/mpls-charter.htm
  l
• RFC3031 MPLS Architecture
• RFC2702 Requirements for TE over MPLS
• RFC3036 LDP Specification
• over 113 RFCs related to MPLS

7
MPLS and OSI(MPLS is a layer 2.5 protocol)
Applications
TCP
UDP
IP
MP?S
MPLS
DWDM
PPP
FR
ATM
Ethernet
Physical
When a layer is added, no modification is needed
on the existing layers.
8
MPLS and OSI(MPLS is a layer 2.5 protocol)
9
Label Switching(This is not new!)

• ATM VPI/VCI
• Frame Relay DLCI
• X.25 LCI (logical Channel Identifier)
• TDM the time slot (Circuit Identification Code)
• Ethernet switching MAC Address

10
Label Substitution (swapping)
Label-A1
Label-B1
Label-A2
Label-B2
Label-A3
Label-B3
Label-A4
Label-B4
11
MPLS

• A protocol to establish an end-to-end path from
  source to the destination
• A hop-by-hop forwarding mechanism
• Use labels to set up the path
• Require a protocol to set up the labels along the
  path
• Support multi-level label transport
• It builds a connection-oriented service on the IP
  network
• Note ATM and Frame Relay also support
  connection-oriented services, but IP does not.

12
Terminology

• LSR - Routers that support MPLS are called Label
  Switch Router
• LER - LSR at the edge of the network is called
  Label Edge Router (a.k.a Edge LSR)
• Ingress LER is responsible for adding labels to
  unlabeled IP packets.
• Egress LER is responsible for removing the
  labels.
• Label Switch Path (LSP) the path defined by the
  labels through LSRs between two LERs.
• Label Forwarding Information Base (LFIB) a
  forwarding table (mapping) between labels to
  outgoing interfaces.
• Forward Equivalent Class (FEC) All IP packets
  follow the same path on the MPLS network and
  receive the same treatment at each node.

13
How does it work?
remove label at the egress LER
Add label at the ingress LER
LSR
LSR
LER
LER
IP
IP
IP Routing
Label Switching
Label Switching
IP Routing
14
MPLS Operation
Label Path R1 gt R2 gt R3 gt R4
15
Label Forwarding Information Base (LFIB)
Note the label switch path is unidirectional. Q
create LFIB for R4 gt R3 gt R2 gt R1
16
Label Encapsulation

• Label information can be carried in a packet in a
  variety of ways
• A small, shim label header inserted between the
  Layer 2 and network layer headers.
• As part of the Layer 2 header, if the Layer 2
  header provides adequate semantics (such as ATM).
• As part of the network layer header (future, such
  as IPv6).
• In general, MPLS can be implemented over any
  media type, including point-to-point, Ethernet,
  Frame Relay, and ATM links. The label-forwarding
  component is independent of the network layer
  protocol.

17
Shim Header

• The Label (Shim Header) is represented as a
  sequence of Label stack entries
• Each Label is 4 bytes (32 bits)
• 20 Bits is reserved for the Label Identifier

Label Identifier Label value (0 to 15 are
reserved) Exp Experimental Use S Bottom of
Stack (set to 1 for the last entry in the
label) TTL Time To Live
18
MPLS and TTL

• TTL Time to Live
• In IP, TTL is used to prevent packets to travel
  indefinitely in the network.
• MPLS uses the same mechanism as IP.
• Why do we need TTL?
• MPLS may interwork with non-MPLS network.
• TTL is in the label header of PPP and Ethernet
  (shim header)
• Not supported in ATM.

19
Forward Equivalent Class (FEC) Classification

• When an unlabeled packet arrives at an ingress
  router, a label has to be applied. A packet can
  be mapped to a particular FEC based on the
  following criteria
• destination IP address
• source IP address
• TCP/UDP port
• class of service (CoS) or type of service (ToS)
• application used
• any combination of the previous criteria.

Ingress Label
FEC
Egress Label
138.120.6.0/24
9
6
20
Label Distribution Protocol (LDP)

• Labels are distributed between LERs and LSRs
  using LDP
• LSRs regularly exchange label and reachability
  information with each other using standardized
  procedures
• Used to build a picture of the network that can
  be used to forward packets
• Label Switch Paths are created by network
  operators similar to PVC and VPN

21
MPLS over ATM/Frame Relay/Ethernet

• A majority of MPLS examples are used to carry IP
  traffic over Ethernet links
• But MPLS can also carry IP traffic over ATM and
  frame relay links

22
MPLS and ATM

• Most carriers backbone are ATM-based. What is
  the process of migrating from ATM to MPLS-based
  backbone?

23
MPLS and ATM

• The label information of MPLS can be carried in
  the ATM VCI field. If two levels of labeling are
  needed, then the ATM VPI field could be used. The
  VCI field, however, is adequate for most
  applications.
• Implementing MPLS on an ATM switch would simplify
  integration of ATM switches and routers. An ATM
  switch capable of MPLS would appear as a router
  to an adjacent router. This approach avoids the
  issues of ATM addressing, routing, and signaling
  schemes.
• Implementing MPLS on an ATM switch does not
  preclude the capability to support a traditional
  ATM control plane (such as PNNI) on the same
  switch.
• The two components, MPLS and the ATM control
  plane, would operate independently with VPI/VCI
  space and other resources partitioned so that the
  components would not interact.
• Two implementation schemes VC-merging vs.
  non-merging

24
ATM LSR - Non-Merging(note this is MPLS over
ATM)
5

• IPPacket

5

• ATMcell

• ATMcell

0
1
3
4
4
4
3
8
171.68

• ATMcell

• ATMcell

• ATMcell

• ATMcell

• ATMcell

• IPPacket

8
2
8

• ATMcell

• ATMcell

• ATMcell

Each ATM VC has its own MPLS label.
25
ATM LSR - VC-Merging
5

• IPPacket

5

• ATMcell

• ATMcell

0
1
171.68
3
3
3
3
3
8

• ATMcell

• ATMcell

• ATMcell

• ATMcell

• ATMcell

• IPPacket

8
2
8

• ATMcell

• ATMcell

• ATMcell

Multiple AMT VCs with the same destination and
QoS are merged on the MPLS network with the same
label.
26
Frame Relay over MPLS Example
R2
R1
Ra
Rb
Rc
Lo loopback interface. Why is it needed? R1 and
R2 legacy frame relay router Ra and Rb Label
Switch Edge Router. Label path is between Ra and
Rb.
27
Frame Relay over MPLS (cont.)
192.168.34.5
192.168.34.1
192.168.34.6
192.168.34.2
IP
IP
IP
68.68.68.2
68.68.68.1
DLCI 514
DLCI 513
IP
lo 3.1.1.2
IP
lo 3.1.1.1
RFC2427
RFC2427
Frame Relay
Frame Relay
FR
RFC 4619
FR
RFC 4619
PHY
MPLS
MPLS
MPLS
PHY
PHY
PHY
L2
L2
L2
PHY
PHY
PHY
Note The IP addresses for MPLS configuration and
Frame Relay are on different IP subnets.
28
MPLS Applications

• Traffic Engineering
• Virtual Private Network (VPN)
• Quality of Service (QoS)

29
Traffic Engineering

• Traffic engineering allows a network
  administrator to select the path between two
  notes and bypass the normal routed hop-by-hop
  paths. An administrator may elect to explicitly
  define the path between nodes to ensure QoS or
  have the traffic follow a specified path to avoid
  traffic congestion at certain hops.
• The network administrator can reduce congestion
  by forcing the frame to travel around the
  overloaded segments. Traffic engineering, then,
  enables an administrator to define a policy for
  forwarding frames rather than depending upon
  dynamic routing protocols.
• Traffic engineering is similar to source-routing
  in that an explicit path is defined for the frame
  to travel. However, unlike source-routing, the
  hop-by-hop definition is not carried with every
  frame. Rather, the hops are configured in the
  LSRs ahead of time along with the appropriate
  label values.
• The administrator could be a centrally located
  program.
• Traffic engineering is an important tool for
  network management. It is NOT a customer service.
  (So you will not see it on a carriers web site.)

30
MPLS Traffic Engineering
Overload !!
LER 4
LER 1
IP
Overload !!
IP
Forward to LSR 2 LSR 3 LSR 4 LSR X
LSR 2
LSR 3

• End-to-End forwarding decision determined by
  ingress node.
• Enables Traffic Engineering

31
MPLS-based VPN

• One of most popular MPLS applications is the
  implementation of VPN.
• The basic concept is the same as ATM transparent
  LAN.
• Using label (instead of IP address) to
  interconnect multiple sites over a carriers
  network. Each site has its own private IP
  address space.
• Different VPNs may use the same IP address space.

32
MPLS VPN - Example
192.168.1.0
192.168.2.0
E1
E1
E3
E3
E2
E1
E2
E2
192.168.4.0
30 E3 -- E1 40 E3 -- E2
-- E1 10 E3 -- E2 20 E3

• E1 30 E2
• 20 E1 40 E2

192.168.3.0
LSP
uni-direction
-- E1 30 E3 -- E2 40 E3
10 E3 -- E1 20 E3 -- E1
30 E2 10 E1 40 E2 20 E1
uni-direction
LSP
33
MPLS VPN Connection Model
MPLS Edge
MPLS Edge
MPLS Core
VPN_A
VPN_A
10.2.0.0
11.5.0.0
VPN_B
VPN_A
10.2.0.0
10.1.0.0
VPN_A
11.6.0.0
VPN_B
10.3.0.0
VPN_B
10.1.0.0
VPN_A 10.2.0.0/24, 11.5.0.0/24, 11.6.0.0/24,
10.1.0.0/24 VPN_B 10.2.0.0/24, 10.1.0.0/24,
10.3.0.0/24 Q For a meshed connection, how many
label paths are needed?
34
Case Study (I) ATT MPLS Private Transport
Network Services

• Features and Benefits
• Advanced Management options
• MPLS-based security
• Meshed topology for any-to-any connectivity
• Traffic prioritization - 4 Classes of Services
  (CoS)
• Service Level Agreements (SLAs)
• Web-based reporting

35
Case Study (II)Verizon Private IP Service (MPLS)

• History
• MCI (Verizon) adopted MPLS on a large scale in
  1998 as a traffic engineering technology on its
  public Internet backbone
• Features and Benefits
• Exceptional Service. 24-hour monitoring customer
  service, and service level agreements (SLAs).
• Any-to-Any Connectivity. Multiple locations are
  connected (meshed topology). You no longer need
  PVCs to communicate between sites rather
• Cost-Effective Solution. Private IP Service
  utilizes existing network infrastructure without
  building and operating a private VPN.
• Intranets and Extranets. Private IP Service
  captures the enhanced networking efficiencies
  associated with an IP-based WAN, bringing
  together all the elements to support e-business
  applications within the company or between
  companies.
• MPLS Technology. Private IP Service provides
  varying Class of Services (CoS) and flexible IP
  routing that optimize networks performance.