1 Multi Protocol Label Switching Presented by: Petros Ioannou Dept. of Electrical and Computer...
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Transcript of 1 Multi Protocol Label Switching Presented by: Petros Ioannou Dept. of Electrical and Computer...
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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!
• w