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Multi Protocol Label Switching

Presented by: Petros IoannouDept. of Electrical and Computer Engineering,

UCY

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What is MPLS?• Multi Protocol:

• Because it works with the Internet Protocol(IP), Asynchronous Transport Mode(ATM) and Frame Relay network protocols

• Label Switching:

• Because it use fixed length label switching similar to ATM or FR

• MPLS forwards packets based on labels

• MPLS simplifies and improve the forwarding function by introducing a connection oriented mechanism inside the connectionless IP networks

• Packets are switched, not routed

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Why MPLS?• IP Routing Disadvantages:

• Connectionless

• No QoS

• Each router has to make independent forwarding decisions based on the IP address

• Routing in Network Layer

• Slower than switching

• Usually designed to obtain shortest path

• Don’t take into account additional metrics

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Why MPLS?

Traffic Engineering

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Why MPLS?• ATM Advantages:

• Connection oriented

• Supports QoS

• Fast packet switching with fixed length packets (cells)

• Integration of different traffic types (voice, data, video)

• ATM Disadvantages:

• Complex

• Expensive

• Not widely adopted

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Why MPLS?

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The Idea

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MPLS Label Format

• MPLS uses a 32-bit label field:

• 20-bit label (a number)

• 3-bit experimental field (usually used to carry IP precedence value)

• 1-bit bottom-of-stack indicator (indicates whether this is the last label before the IP header)

• 8-bit TTL (equal to the TTL in the IP header)

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MPLS Label Format

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MPLS Terminology• LSP: Label Switched Path

• An MPLS virtual circuit

• A path established before the data transmission starts

• FEC: Forwarding Equivalence Class

• A group of IP packets which are forwarded in the same manner (over the same path with the same forwarding treatment)

• LSR: Label Switching Router

• Any router in network who supports MPLS

• LER: Label Edge Router

• Resides at the edge of an MPLS network and assigns and removes the labels from the packets

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MPLS Operation

PUSH SWAP POP

IngressRouter

EgressRouter

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Establishing a Label Switched Path

• Each LSR negotiates a label for each Forwarding Equivalence Class (FEC) with its neighbors using a distribution method

• The result of negotiation is a Label Information Base (LIB)

• Each LSR maintains a Label Information Base (LIB) and learns labels from there

• When next hop changes for a FEC, LSR will retrieve the label for the new next hop from the LIB

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Label Distribution Protocols• Label Distribution Protocol (LDP)

• Hop-by-Hop label distribution

• Follows IGP-OSPF best path

• No traffic engineering capabilities

• Highly scalable

• Best suited for apps using thousands of LSPs (VPNs)

• Resource Reservation Protocol with Traffic Engineering Extensions (RSVP-TE)

• End-to-End LSP signaling

• Enables different specifications on each path

• Less scalable

• Best suited for traffic engineering in the core

• Constraint-Based Routed LDP (CR-LDP)

• TE-capable LDP

• Never widely deployed

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Label Distribution Protocol (LDP)

• A protocol which it is used to map FECs to labels

• In order to do that LDP sessions are established between LDP peers in the MPLS network

• LDP message types:

• discovery messages: announce and maintain the presence of an LSR in a network

• session messages: establish, maintain, and terminate sessions between LDP peers

• advertisement messages: create, change, and delete label mappings for FECs

• notification messages: provide advisory information and signal error information

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Label Distribution Protocol (LDP)

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Traffic Engineering• A way to achieve required delay, grade-of-

service and to meet policy requirements imposed by the network operator

• Traffic Engineering ensure available spare link capacity for re-routing traffic on failure

• In case of single failure the network traffic is spread across network backup links

• The LSPs are created independently, specifying different paths that are based on user-defined policies

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Traffic Engineering

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Resource Reservation Protocol with Traffic Engineering Extensions (RSVP-TE)• Request bandwidth and traffic conditions on a defined path

• Uses two types of massages: RSVP PATH msg and RSVP RESERVATION msg

• Calculates best path based on the specified constraints

• TE interface parameters:

• Maximum Bandwidth

• Maximum Reservable Bandwidth

• Unreserved Bandwidth

• TE Metric (given by IGP protocol)

• Administrative Group (Link Affinity or “Link Coloring”)

• Drawback:

• Requires regular refreshes

• Scalability

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Resource Reservation Protocol with Traffic Engineering Extensions (RSVP-TE)

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Benefits from MPLSMPLS combines the performance characteristics of layer 2 networks and the connectivity and network services of layer 3 networks•Combines IP and ATM in the network•Improves packet-forwarding performance in the network•Supports network scalability•Improves the possibilities for traffic engineering•Supports the delivery of services with QoS guarantees

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Thank You!

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