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Tag/Label Switching

Tag/Label Switching. CS598: Advanced Internet Presented by: Imranul Hoque. How to go from A to B?. Broadcast: Go everywhere, stop at B Never ask for directions Hop by hop routing: Ask who is closer to B, go there, repeat! You better go to X first … Source routing:

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Tag/Label Switching

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  1. Tag/Label Switching CS598: Advanced Internet Presented by: Imranul Hoque

  2. How to go from A to B? • Broadcast: • Go everywhere, stop at B • Never ask for directions • Hop by hop routing: • Ask who is closer to B, go there, repeat! • You better go to X first … • Source routing: • Get a list before starting • Go straight 5 blocks, take a left, 4 more blocks, …

  3. How to go from A to B? • Let someone go ahead of you • At every road reserve a lane for you • At intersection, post a sign (turn + lane) Lane #1 Lane #2 Lane #2: turn left, use lane #1

  4. What is it good for? • Enable IP capabilities on devices that cannot forward IP datagrams • Explicit routing – pre-calculated routes that do not match normal IP routing paths • Virtual Private Network (VPN) services

  5. What is it good for? • Enable IP capabilities on devices that cannot forward IP datagrams • Explicit routing – pre-calculated routes that do not match normal IP routing paths • Virtual Private Network (VPN) services One of the original goals is not on the list!

  6. This Talk • History • Learn from Examples • Destination-based Forwarding • Explicit Routing • Virtual Private Networks and Tunnels • Points to Ponder • What layer is MPLS? • Where is MPLS now?

  7. History • Ipsilon Networks • IP switching, defined to work on ATM • Cisco Systems, Inc. • Tag switching, proprietary proposal • Renamed label switching • Handed over to IETF • IETF • Proposals from other vendors (Toshiba, IBM)

  8. Destination-Based Forwarding

  9. Benefits • Exact match, as opposed to longest match • Simple to implement in hardware • Forwarding Equivalence Class (FEC) • Set of packets that receive same forwarding treatment • Devices not supporting IP can forward IP traffic • Example: carry IP traffic over ATM switches • How and Why?

  10. How? • Provide switches with: • IP routing protocols • A method to distribute label bindings (LDP) • Result: IP control protocols with label-swapping forwarding

  11. Why? Set of routers connected over an ATM network (why?) ATM switches are replaced with LSR (benefits?)

  12. Explicit Routing • Questions: • How to routers agree on what labels to use and how to forward packets with particular labels?

  13. Applications of Explicit Routing • Traffic Engineering • Controlling exactly which path the traffic flows • Resilience in face of failure • Reroute traffic down a pre-calculated path • Known as Fast Reroute

  14. Applications of Explicit Routing • Traffic Engineering • Controlling exactly which path the traffic flows • Resilience in face of failure • Reroute traffic down a pre-calculated path • Known as Fast Reroute How to calculate the explicit routes?

  15. Virtual Private Networks • “Layer 2” VPN • Tunnel layer 2 data (Ethernet frames/ATM cells) • Pseudo-wire emulation

  16. Virtual Private Networks • “Layer 2” VPN • Tunnel layer 2 data (Ethernet frames/ATM cells) • Pseudo-wire emulation What to do with non-IP traffic when it reaches the EOT?

  17. VPN: ATM over IP • Labels may be stacked on a packet to any depth • A single tunnel can carry potentially large number of emulated circuits • Same technique to provided hierarchy of routing knowledge

  18. What Layer is MPLS? • Layer 2.5 • Layer 2 • Layer 3

  19. What Layer is MPLS? • Layer 2.5 • MPLS header is found between layer 3 and layer 2 headers • Layer 2 • IP packets are encapsulated inside MPLS headers • MPLS must be below IP • Layer 3 • MPLS uses IP routing protocols and IP addressing

  20. Where is MPLS Now? • Sufficiently popular among service providers • Almost all high-end routers include MPLS capabilities • Two main applications: • Layer 3 VPN: Provide “private” IP services to corporations • Explicit Routing: TE and/or Fast Reroute • Difficult to determine how many providers are actually using this technology

  21. Questions?

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