MPLS,Multi Protocol Label Switching

1
MPLS,Multi Protocol Label Switching

• SITE, UOttawa
• Wael Hassan

2
Introduction

• Need for Seamless Networks
• Need for IP/ATM integration
• IP Reachability / ATM QoS
• Current Alternatives
• IP Over ATM
• IP MPLS ATM

3
MPLSdefined

• MPLS or Multi-protocol Label Switching. Is a
  Method for forwarding packets( frames) through a
  Network. There are two major types
• of MPLS networks (industry)
• MPLS running on MPLS networks(over IP).
• MPLS Carried over ATM Switches.(most likely)
• Why MPLS?
• -It can be carried transparently over ATM
  networks.
• -It reduces the overhead of PVC configurations in
  ATM.

4
MPLS Label

• The label summarizes essential information about
  routing the packet
• Destination
• Precedence
• Virtual Private Network membership
• Quality of Service (QoS).
• The route for the packet, as chosen by traffic
  engineering (TE)

5
MPLS Network Structure

• Edge Label Switch Routers
• Edge Label Switch Routers are located at the
  boundaries of a network, performing value-added
  network layer services and applying labels to
  packets. These devices can be either routers or
  router/Switches.
• Label Switch (ATM or IP Or Label Switches)
• These devices switch labeled packets or cells
  based on the labels. Label switches may also
  support full Layer 3 routing or Layer 2 switching
  in addition to label switching.

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MPLS in IP Implementations Cisco

• MPLS over IP interfaces
• IP packets enter into the edge of the MPLS
  network.
• The edge LSR invoke CAR(Committed Access Rate) to
  classify the IP packets and to set IP precedence
  bits. Alternatively, these IP packets might have
  the precedence set.
• Each core router performs a lookup in the IP
  address to determine the next-hop LSR.
• The appropriate Label is placed on the packet
  with the IP precedence buts copied into the MPLS
  header.
• The Labeled packet is then forwarded to the
  appropriate output interface for processing.
• The packets are differentiated by class. Using
  WRED ( Weighted Random Early detection and WFQ
  Weighted Fair Queuing.

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MPLS in ATM Implementations Alcatel

• MPLS over ATM (Mocked)(1)
• MPLS Packet is packetized into ATM 53 byte
  packets. The ATM Header is replaced by an MPLS
  tag. The packets are switched in the network
  using regular ATM switching/routing protocols.
• NATIVE MPLS over ATM (2)
• Requires Packet over sonnet capabilities(POS)
• The MPLS packets using a sonnet interface are
  piped through the network using PVC connections

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(2)LSR Label Switching Router

• LSR (Label Switching Router)
• At the edge of an ATM network were ATM traffic
  needs to flow, an LSR is needed. The LSR picks
  MPLS packets coming from IP network routers.
• With Label Switching the complete analysis of the
  Layer 3(Network) header is performed only once
  at the edge label switch router (LSR), which is
  located at each edge of the network.
• At this location, the Layer 3 header is mapped
  into a fixed length label, called a Label."
• At each router/Switch across the network, only
  the label need be examined in the incoming cell
  or packet in order to send the cell or packet on
  its way across the network.
• At the other end of the network, an edge LSR
  swaps the label out for the appropriate header
  data linked to that label.

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(1)Label Switching Benefits

• MPLS offers many advantages over traditional IP
  over ATM.
• When integrated with ATM switches, label
  switching uses the advantage of switch hardware
  optimized to take advantage of the fixed length
  of ATM cells and to switch the cells at high
  speeds.

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Label Switching Operation at Layer 3

• ForwardingForwarding uses the label information
  to perform packet forwarding.
• ControlThe control component maintains the
  correct label-forwarding information along with a
  group of interconnected label switches.

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IP Solution (Forwarding)
128.89.25.4 Data
RouterA
128.89.0.0/16
RouterC
128.89.25.4 Data
9 128.89.25.4 Data
RouterB
171.69.0.0/16
RouterD
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IP Solution (Forwarding)

• UnLabeled IP packet with destination 128.89.25.4
  arrives at RouterA.
• A checks its LFIB(Label Forwarding Information
  Base) and matches destination with 128.89.0.0/16.
• Labels the packet with an outgoing label of 4 and
  sends it to its next hop Router B.
• B receives the packet with an incoming label of
  4. 4 is used as an index to search for in LFIB .
• Swap Label 4 with Label 9.
• The packet is sent out on Interface 0 with the
  appropriate Layer 2 information (MAC address)
  according to the LFIB. Here we did not do any IP
  address lookups.
• When Router C receives the packet it removes the
  label and forwards it as an unlabeled IP packet.

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IP Solution (Control Component)

• The control component of MPLS consists of IP
  routing protocols. The control component is
  responsible for setting up label forwarding paths
  along IP routes, and then distributing these
  label bindings to label switches. LDP or Label
  Distribution protocol is a major port of the
  control component.

LDP For each Route in the routing table, the LSR
allocates a label and creates an entry in
LFIB. The Label switch router then advertises the
binding between the label (incoming) it created
and the route to other adjacent label switch
routers. When a Label switch router receives
Label binding information for a route and the
information was originated by the next hop for
that route, the switch places the label into the
outgoing label of the LFIB entry associated with
the route.
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IP Solution (LDP)
Prefix 128.89.0.0/16, Label 4
A
LDP
Prefix 128.89.0.0/16, Label 9
Out Label 4 Prefix128.89.0.0/16 Label X
B
LDP
Out Label 9 Prefix128.89.0.0/16 Label 4
C
Out Label 9 Prefix128.89.0.0/16 Label X
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ATM Solution
128.89.25.4 Data
RouterA
128.89.0.0/16
RouterC
128.89.25.4 Data
9 128.89.25.4 Data
RouterB
171.69.0.0/16
RouterD
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ATM Solution

• An Unlabeled IP packet with destination
  128.89.25.4 arrives at A.
• A matches its prefix with 128.89.0.0/16.
• A converts the AAL5 frame to cells and send the
  frame out as a sequence of cells on VCI40.
• B performs normal switching operation by
  switching incoming cells on interface 2/VCI 40 to
  interface 0/VCI 50.

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Benefits

• These MPLS benefits are analyzed in greater
  detail
• Integration
• When applied to ATM, MPLS integrates IP and
  ATM functionality rather than overlaying IP on
  ATM. This makes the ATM infrastructure visible
  to IP routing and removes the need for
  approximate mappings between IP and ATM features.
  MPLS does not need ATM addressing and routing
  techniques such as PNNI, although these can be
  used in parallel if required.
• Reduce IP over ATM OverheadTraditional IP over
  ATM involves setting up a mesh of Permanent
  Virtual Circuits (PVCs) between routers around an
  ATM cloud, and the Next Hop Resolution Protocol
  (NHRP) achieves a similar result with switched
  virtual circuits (SVCs). But there are a number
  of problems with this approach, all arising from
  the method that the PVC links between routers are
  overlaid on the ATM network. This makes the ATM
  network structure invisible to the routers. A
  single ATM link failure could make several
  router-to-router links fail, creating problems
  with large amounts of routing update traffic and
  subsequent processing.
• PNNI Public Network Node Interface

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MPLS Advantages

• Better EfficiencyWithout extensive tuning of
  routing weights all PVCs are seen by IP routing
  as single-hop paths with the same cost. This
  might lead to inefficient routing in the ATM
  network. This does not happen with MPLS.
• Direct Classes of Service ImplementationWhen
  used with ATM hardware, MPLS makes use of the ATM
  queuing and buffering capabilities to provide
  different Classes of Service (COS). This allows
  direct support of IP Precedence and COS on ATM
  switches without complex translations to the ATM
  Forum Service Classes.

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Benefits

• Traffic Engineering CapabilitiesOther benefits
  of MPLS include traffic engineering (TE)
  capabilities needed for the efficient use of
  network resources. Traffic engineering enables
  you to shift the traffic load from over utilized
  portions to underutilized portions of the
  network, according to traffic destination,
  traffic type, traffic load, time of day, and so
  on.
• MPLS enables network-based IP-VPNs a service
  offered by the network service provider that
  appears to the customer as a private network.
  VPNs benefit from MPLS because of the notion of
  paths. Once routed onto a specific path, traffic
  will follow the path without needing to be
  analyzed at every hop. Therefore, MPLS paths
  allow the complexity of VPNs with sophisticated
  classification rules, overlapping addresses and
  many distinct forwarding tables to be hidden from
  core nodes. This enhances Scalability.

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Industry trends for QOS

• Companies like (Nortel,Alcatel, Marconi)
  providing carrier scale products always use ATM
  capabilities to provide Qos capabilities to MPLS.
  
• However, companies like Cisco who were the
  darlings for smaller more numerous service
  providers originally strong in smaller scale
  routers use alternative methods, COS or class of
  service is an example.
• IP market segment is already big and is growing.
  Companies like (Alcatel) are recognizing this
  fact and hence are trying to integrate IP into
  their products. A large portion on the North
  American market is ore for IP

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MPLS Class of Service

• Packet Classification
• IP PrecedenceThis feature uses 3 bits in the IP
  header to indicate class of service of a packet
  (1-8). This value is set at the edge and inforced
  in the core. Different Labels are used to
  indicate different service levels.
• Packet Classification by Committed Access
  Rates(CAR)Uses the Type of Service (TOS) ltgt
  Class of Service (COS) bits in the IP header to
  classify packets according to input and output
  transmission rates. CAR is often configured on
  interfaces at the edge of the network to control
  ingress and egress traffic.
• Congestion avoidanceWeighted random early
  detection (WRED). Packet classes are
  differentiated based on drop probability. WRED
  monitors network traffic trying to anticipate and
  prevent congestion. It drops (lower priority)
  packets accordingly.
• Congestion ManagementWeighted fair queuing
  (WFQ). Packet classes are differentiated based on
  bandwidth and bounded delay. WFQ is an automated
  scheduling system that provides fair bandwidth
  allocation to all network traffic. WFQ uses
  priorities to determine how much bandwidth each
  class of traffic is allocated.

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QoS

• CISCO Model
• QoS is not a device feature it is an end-to-end
  system architecture. A robust QoS solution
  includes a variety of technologies that
  interoperate to deliver scalable,
  media-independent services throughout the
  network, with system-wide performance-monitoring
  capabilities.
• The actual deployment of QoS in a network
  requires a division of labor for greatest
  efficiency. Because QoS requires intensive
  processing, the Cisco model distributes QoS
  duties between edge and core devices that could
  be multilayer switches or routers. Edge devices
  do most of the processor-intensive work,
  performing application recognition to identify
  flows and classify packets according to unique
  customer policies. Edge devices also provide
  bandwidth management. Core devices expedite
  forwarding while enforcing QoS levels assigned at
  the edge.
• There are reasons why providing QoS for IP
  traffic is fundamentally different from providing
  QoS in Connection oriented networks. Connection
  Oriented QoS is based on the premise that most
  traffic has QoS requirements that must almost
  always be met in order to provide adequate
  performance. Most IP applications, on the other
  hand, are tolerant of widely varying bandwidth
  they can tolerate periods of seconds or more of
  high loss and are usually extremely tolerant of
  delay and delay variance. CISCO.

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References

• The Cisco "IPATM Solutions" page at
  http//www.cisco.com/go/ipatm
• The OSPF version 2 specification is
  http//www.ietf.org/rfc/rfc2328.txt
• The "IS-IS for Routing in TCP/IP and Dual
  Environments" specification is http//www.ietf.org
  /rfc/rfc1195.txt
• IETF documents on MPLS are at http//www.ietf.org/
  html.charters/mpls-charter.html.
• "MPLS Architecture" draft-ietf-mpls-arch-05.txt
• "MPLS Label Stack Encodings" draft-ietf-mpls-label
  -encaps-04.txt
• "MPLS using LDP and ATM VC Switching"
  draft-ietf-mpls-atm-02.txt
• "LDP Specification" draft-ietf-mpls-ldp-05.txt
• "MPLS Support of Differentiated Services by ATM
  LSRs and Frame Relay LSRs" draft-ietf-mpls-diff-ex
  t-01.txt
• Other IETF documents on Differentiated Services
  are at http//www.ietf.org/html.charters/diffserv-
  charter.html
• The most important IETF documents on the Border
  Gateway Protocol are
• "A Border Gateway Protocol 4 (BGP-4)"
  http//www.ietf.org/rfc/rfc1771.txt
• "Multiprotocol Extensions for BGP-4"
  http//www.ietf.org/rfc/rfc2283.txt
• A further informational document shows how BGP
  can be used to support VPNs"BGP/MPLS VPNs," RFC
  2457, http//www.ietf.org/rfc/rfc2547.txt
• The following books on routing, MPLS and related
  topics are very useful
• Halabi, B., Internet Routing Architectures, Cisco
  Press, 1997.
• Metz, C., IP Switching Protocols and
  Architectures, McGraw-Hill, 1999
• Rekhter, et al., Switching in IP Networks, Morgan
  Kaufmann, 1998
• Useful magazine articles are