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MPLS - Introduction

MPLS - Introduction. Multi-protocol Label Switching. Issues. Price and performance Scalability Flexibility of routing functionality Tight coupling between routing and forwarding algorithms. IP Over ATM. ATM. Extending Router Functionality. D. A. F. C. B. E. History.

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MPLS - Introduction

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  1. MPLS - Introduction Multi-protocol Label Switching CSE 8344

  2. Issues • Price and performance • Scalability • Flexibility of routing functionality • Tight coupling between routing and forwarding algorithms CSE 8344

  3. IP Over ATM ATM CSE 8344

  4. Extending Router Functionality D A F C B E CSE 8344

  5. History • Cell switching router (CSR) • Toshiba • IP switching • Ipsilon • Tag switching • Cisco CSE 8344

  6. IP Switching CSE 8344

  7. IP Switching • Introduced by Ipsilon • Significant innovations • General switch management protocol (GSMP) • Label binding protocol, Ipsilon flow management protocol (IFMP) • GSMP allows an ATM switch to be controlled by an “IP switch controller” CSE 8344

  8. IP Switching Premise • IP over ATM models are complex and inefficient - involve running two control planes • ATM signaling and routing • IP routing and address resolution on top • In contrast IP Switching uses • IP component plus label binding protocol • Completely removes ATM control plane • Goal: To integrate ATM switches and IP routing in a simple and efficient way CSE 8344

  9. IP ATM MARS NHRP ARP PNNI Q.2931 ATM hardware Removing ATM Control Plane • (a) IP over Standard ATM • (b) IP Switching IP IFMP ATM hardware (a) (b) CSE 8344

  10. IP Switching Architecture • Switch controller • Control processor of the system • Uses GSMP to communicate with ATM switch • Runs IP routing and forwarding code • Default VC • To get control traffic before IP Switching is performed • Uses well known VCI/VPI value • Used for data that doesn’t have a label yet

  11. Switch controller Flow Classification and control To downstream switch To upstream switch Routing and forwarding IFMP GSMP GSMP Default VC Default VC Data VC Data VC Switch IP Switch Architecture CSE 8344

  12. Switching Basics • Relies on IP protocols • To establish routing information • To determine next hop • Flow classification and control module selects flows from incoming traffic • IP flow refers to a sequence of datagrams • from one source to one destination, identified by the ordered pair <source address, destination address> • can also refer to a flow at finer granularity, e.g., different applications between same pair of machines, identified by < source address, source port, destination address, destination port>

  13. Flow Redirection • Redirection: Process of binding labels to flows and establishing label switched paths • Example: • data is flowing from A via B to C on default VC • B sends a redirect to A specifying flow y and the label (VPI/VCI) on which it expects to receive • If C issues a redirect to B for flow y, B forwards y on the VPI/VCI specified by C • Since same flow y enters B on one VC and leaves on another, B uses GSMP to inform its switching element to set up the appropriate switching path

  14. Redirect:Flow y VPI/VCI 3/57 Switch Controller B Switch B issues a REDIRECT message to switch A A A C Redirect:Flow y VPI/VCI 3/57 Redirect:Flow y VPI/VCI 2/22 Default VC Default VC Switch Element Switch Controller B C 3/57 Default VC Default VC Switch Element 3/57 2/22 Switch B and C redirect the same flow, allowing it to be switched at B Flow Redirection

  15. Ipsilon Flow Management Protocol (IFMP) • Designed to communicate flow to label binding information • IFMP is a soft state protocol • IFMP’s Adjacency Protocol: • Used to communicate and discover information about neighbors • Adjacency message sent as limited broadcast • IFMP’s Redirection Protocol • Used to send appropriate messages for flow-label bindings CSE 8344

  16. Adjacency Protocol • To exchange initial set of information • ADJACENCY message encapsulated into IP datagram and sent to limited broadcast address • Also used to agree on the sequence numbers CSE 8344

  17. IFMP’s Redirection Protocol • Different message types defined: • REDIRECT: used to bind label to a flow • RECLAIM: enables label to be unbound for subsequent re-use • RECLAIM ACK: Acknowledgement for RECLAIM message • ERROR: Used to deal with various error conditions • Common header format CSE 8344

  18. IFMP Redirect Protocol Message Format IFMP REDIRECT message body

  19. Encapsulation of IP packet on the default VC Encapsulation of IP packet on the redirected VCs Encapsulation of Redirected Flows CSE 8344

  20. General Switch Management Protocol (GSMP) • GSMP is a master/slave protocol • ATM switch is the slave • Master could be any general purpose computer • The protocol allows the master to • Establish and release VC connections across the switch • Perform port management (Up, Down, Reset, Loopback) • Request Data (configuration information, statistics) • Allows slave to inform master of events such as link failure CSE 8344

  21. GSMP (cont’d) • GSMP packets are LLC/SNAP encapsulated and sent over ATM link using AAL5 • GSMP Adjacency Protocol • Used to gain information about the system at the other end of the link and • To monitor link status • GSMP Connection Management Protocol • Used to ensure consistency between the GSMP master and slave • Specifies the QoS using a priority field CSE 8344

  22. Tag Switching CSE 8344

  23. Design Goals • Adding functionality • Explicit routing • Improve scalability • Hierarchy of routing knowledge • Link layer independent • Not just ATM • Implemented in a variety of devices such as routers and ATM switches CSE 8344

  24. Terminology Comparison CSE 8344

  25. Destination Based Routing • A TSR uses information from unicast routing protocols to construct its mapping between FECs and next hops • This mapping is used by the Tag Switching Control component for constructing the TFIB which is used for actual packet forwarding CSE 8344

  26. Construction of TFIB • A local binding between the FEC and a tag • Takes a tag from the pool of free tags and uses it as an index in the TFIB to set the incoming tag entry • A mapping between the FEC and the next hop for that FEC (provided by the routing protocol(s) running on the TSR) • A remote binding between the FEC and a tag that is received from the next hop CSE 8344

  27. A B if0 if1 if2 if1 E if2 if0 if0 if1 if2 if0 if2 if1 if0 TSR C D Example 192.6/16 CSE 8344

  28. Initial TFIB Entries For FEC 192.6/16 CSE 8344

  29. TFIB Entries After Tag Distribution CSE 8344

  30. A B if0 if1 if2 if1 E if2 if0 if0 if1 if2 if0 if2 if1 if0 TSR C D Behavior With Routing Change Link Down CSE 8344

  31. Updated TFIB CSE 8344

  32. Hierarchical Routing • Scalability • Faster convergence • Fault isolation CSE 8344

  33. Hierarchy of Routing Knowledge • All TSRs within a routing domain participate in a common intra-domain routing protocol and construct TFIB corresponding to destinations within the domain • All border TSRs or TERs within a domain and directly connected TERs from other domains also exchange Tag binding information via inter-domain routing protocol CSE 8344

  34. Hierarchy (Cont’d) • To support forwarding,Tag switching allows a packet to carry several tags organized as a tag stack • At the ingress, a tag is pushed onto the tag stack, and at the egress a tag is popped off the stack CSE 8344

  35. Routing domain C Routing domain B Routing domain A V T X Y W Z TSR Hierarchical Routing Model CSE 8344

  36. TFIB Entries in Routing Domain A CSE 8344

  37. Top of Stack 10 Top of Stack 2 2 Stack after processing in TSR T Stack after processing in TSR W Label Stack TSR Z distributes label 2 to TSR W and TSR W gives label 5 to TSR T for the purpose of inter-domain routing CSE 8344

  38. Multicast in Tag Switching • Selects the distribution tree based only on • tag carried in a packet • interface on which the packet arrives • TSR maintains its TFIB on a per interface basis • TSRs connected to a common sub-network agree among themselves on a common tag associated with a particular multicast tree CSE 8344

  39. Multicast (Cont’d) • Partition the set of tags for use with multicast into disjoint subsets • Avoid overlap with the help of HELLO packets • TSR connected to a common sub-network and those which are a part of the same distribution tree elect one TSR that will create the tag bindings and distribute them • any TSR can join the group using the JOIN command CSE 8344

  40. A B if0 D if0 if1 if2 if0 if0 TSR E F Multicast Model CSE 8344

  41. RSVP With Tag Switching • RSVP supported with the help of a RSVP object - the tag Object • The tag object binding for an RSVP flow carried in the RSVP “RESV” message • The RESV message carries the tag object containing the tag given by a TSR and also information about the local resources to be used • The reservation state is refreshed once the flow is set up using the RESV message CSE 8344

  42. Explicit Routes • Tag switching supports explicit routes with the help of Explicit Route Object • The object is carried in the RSVP “PATH” message • The tag information is carried in the Tag Object by the RSVP “RESV” CSE 8344

  43. Tag Switching Over ATM • VCI field used as tag field • For stacks, use VPI • Cell interleave problem • VC merge • Different tags on the same path CSE 8344

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