MPLS Tutorial ETSI June 99

1. MPLS TutorialETSI June 99 Francois Le Faucheur Systems Architect Cisco Systems flefauch@cisco.com Cisco Systems

2. Agenda • Label Switching Technology Overview • History & Motivation • Destination-Based Routing • Label Distribution Protocol(s) • Encapsulation • MPLS Over ATM • Applications • Quality of Service • Traffic Engineering • VPNs • Conclusion: Gbit Routing or MPLS? Cisco Systems

3. Label Switching Motivation • Address major network evolution problems: • Throughput • Scaling • Number of nodes, flows, routes • Traffic engineering (explicit routes) • Permit graceful evolution of routing • Flexibility, new applications • Simplify integration of ATM and IP Cisco Systems

4. Label Switching Basics • Combines Layer 3 routing with label-swapping forwarding • Simplicity of Layer 2 forwarding offers high performance • Layer 3 routing has proven scalability • Clean separation of Forwarding and Control/Routing • Forwarding component: Simple label-swapping paradigm • Control component: Collection of modules to maintain and distribute label bindings • Separation leads to graceful evolution of control paradigm Cisco Systems

5. Label Switching Devices Label Switching Routers (LSRs) (ATM Switch or Router) Label Edge Routers Cisco Systems

6. Forwarding Component • Label Forwarding Information Base (LFIB) • Each entry consists of: • Incoming label • One or more sub-entries: • Outgoing label, outgoing interface, outgoing MAC address • LFIB is indexed by incoming label Cisco Systems

7. Forwarding Component (Cont.) • Forwarding algorithm: • Extract label from a packet • Find LFIB entry withincoming label = label from packet • Replace label in packet with outgoing label(s) • Send packet on outgoing interface(s) • Observation: forwarding algorithm is • Network Layer-independent • independent of how labels have been assigned (ie by Control module) Cisco Systems

8. 128.89.10 1 128.89.10 0 171.69 1 171.69 1 ... ... Label Switching Example Destination-Based Routing Module Address Prefix Address Prefix Interface Interface 128.89.10 Advertises Reachability to 128.89.10 i/f 0 i/f 1 i/f 1 Advertises Reachability to 128.89.10 and 171.69 171.69 Advertises Reachability to 171.69 Cisco Systems Confidential 0675_03F7_c3 10

9. 128.89.10 1 128.89.10 0 171.69 1 171.69 1 ... ... Label Switching Example (Cont.) Address Prefix Address Prefix Interface Interface 128.89.10 Advertises Binding <5,128.89.10> Using LDP i/f 0 i/f 1 i/f 1 Advertises Bindings <3,128.89.10> <4,171.69> Using LDP 171.69 Advertises Binding <7,171.69> Using LDP 11

10. Local Label Remote Label Address Prefix Local Label RemoteLabel Address Prefix Interface Interface Label Switching Example (Cont.) 128.89.10 0 3 5 128.89.10 1 x 3 4 7 171.69 1 x 4 171.69 1 ... 128.89.10 ... 0 1 1 7 171.69.12.1 data 171.69.12.1 data 4 171.69.12.1 data 171.69 ‘Edge’ Router Does Longest Match, Adds Label Subsequent Routers Forward on Label Only Cisco Systems

11. Label Distribution Protocol (LDP) • Used to distribute <label,prefix> bindings • Incremental updates over reliabletransport • One of several label-binding mechanisms Cisco Systems

12. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label | Exp |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Frame Encapsulation • Can be used over Ethernet, 802.3, or PPP links • new Ethertypes/PPP PIDs • Contains everything needed at forwarding time • MPLS Headers can be used “recursively” S = Bottom of Stack TTL = Time to Live EXP = Experimental (formerly COS = Class of Service) Cisco Systems

13. Label Switching and ATM • label switching forwarding: • Make decision using fixed length label • Rewrite the label with a new value • Sounds like ATM • label switching control: • Based on L3 protocols • used to set-up/maintain ATM VCs (instead of traditional ATM Control plane protocols UNI/PNNI) • Resolves ‘impedance mismatch’ Cisco Systems

14. Label Distribution for ATMDownstream on Demand Output i/f Local Label Address Prefix Remote Label Input i/f Requests a labelfor 128.89 128.89 0 1 5 7 6 0 2 8 128.89 ... 128.89 Requests Two Labels for 128.89 Returns a Label to Each Requester Requests a labelfor 128.89 Label Switching = ATM switching because labels copied in VCI Cisco Systems

15. MPLS ATM Impedance Mismatch • Downstream on Demand • label conservation • VC-Merge • Cell Interleave • Loop prevention • Hop count fields in request and response • Per-VC queuing to limit damage • loop detection • optional loop prevention • TTL semantics • Decrement by hop count on ingress • Use ‘router alert’ to handle traceroute Cisco Systems

16. Scaling in L2/L3 Networks Problem: Huge Number of Routing Adjacencies Impacts Routing Performance Cisco Systems

17. Scaling in MPLS Networks Solution: Only Neighbor-Neighbor Routing Adjacencies Cisco Systems

18. Agenda • Label Switching Technology Overview • History & Motivation • Destination-Based Routing • Label Distribution Protocol(s) • Encapsulation • MPLS Over ATM • Applications • Quality of Service • Traffic Engineering • VPNs • Conclusion: Gbit Routing or MPLS? Cisco Systems

19. MPLS QoS • MPLS targets support of existing IETF QoS models (does not reinvent a new QoS model): • Diff-Serv over MPLS • Int-Serv over MPLS • targeted result is end-to-end IP QoS through MPLS clouds indistinguishable from IP QoS in non-MPLS network Cisco Systems

20. Diff-serv on ATM-LSRs • Challenges: • No DS field in header • Re-ordering constraints of Diffserv • Different drop algorithms in switches (ie no RED/WRED) • Solution approach: • Use parallel LSPs to one destination (FEC) • Each LSP represents a group of PHBs (ie the PHBs with ordering constraint)eg. EF, Default, AF1x, AF2x, AF3x, AF4x --> one LSP per <FEC, PHB group> • CLP to indicate drop preference within PHB group Cisco Systems

21. Parallel LSPs EF • PHB Group (ie EF, AF1x, AF2x,..) signaled at label establishment time • Switch performs scheduling based on PHB Group : • eg. all AF1x labels into the same queue • eg. Switches perform per-class WFQ (not per-VC) • Switch performs “drop precedence” based on CLP bit AF1 AF2 Cisco Systems

22. Diff-Serv on PPP LSR • Two complementary approaches pursued and allowed simultaneously • Similar to Diff-Serv over ATM LSR • ie Parallel LSPs • PHB Group is signaled at LSP set-up • use MPLS Shim Header EXP field to convey Drop Precedence • use MPLS EXP field exactly as DSCP is used for IP • takes advantage of fact that MPLS EXP field is seen at every PPP LSR hop • use MPLS EXP field to indicate the PHB Group as well as the Drop Precedence • limit to total 8 PHBs Cisco Systems

23. Int-Serv over MPLS • Each RSVP session has dedicated label • label binding carried in RSVP RESV and PATH messages • Enables simple flow classification (label vs. src and dest address and port) • Note: this is for establishment of a label per RSVP flow (as opposed to using RSVP to set up labels for fat aggregates for Traffic Engineering) • Stable I-D but not high priority of MPLS group Cisco Systems

24. Agenda • Label Switching Technology Overview • History & Motivation • Destination-Based Routing • Label Distribution Protocol(s) • Encapsulation • MPLS Over ATM • Applications • Quality of Service • Traffic Engineering • VPNs • Conclusion: Gbit Routing or MPLS? Cisco Systems

25. IP Routing & “the Fish” R8 R3 R4 R5 R2 R1 R6 R7 IP (Mostly) Uses Destination-Based Least-Cost Routing Flows from R8 and R1 Merge at R2 and Become Indistinguishable From R2, Traffic to R3, R4, R5 Use Upper Route Alternate Path Under-Utilized 6

26. MPLS Traffic Engineering • MPLS TE is not about offering additional QoS services visible by end-user • MPLS TE is about reducing cost of providing end-user services (eg Diff-Serv) through better use of given resources • May improve QoS • MPLS TE takes advantage of “connection-like” nature of MPLS to distribute traffic based on Bandwidth demand/use • like current Voice Traffic Engineering Cisco Systems

27. MPLS TE Tunnel R8 R3 R4 R5 R2 R1 R6 R7 Labels, like ATM VCs can be used to establish virtual circuits which are “Qos Routed” Normal Route: R1->R2->R3->R4->R5 TE Tunnel: R1->R2->R6->R7->R4->R5 0401_10F8_c1 NW97_EMEA_504 6

28. MPLS TE • TE Tunnels need be “automatically” routed • performs Constraint Based Routing where constraints include: • Bandwidth need of a tunnel versus bandwidth available on all links • Policy constraint configurable by Operator (eg that sort of Tunnel must not use that sort of links) Cisco Systems

29. POP4 POP POP POP POP2 POP1 TE Example Deployment Find route & set-up tunnel for 20 Mb/s from POP1 to POP4 Find route & set-up tunnel for 10 Mb/s from POP2 to POP4 WAN area Cisco Systems

30. MPLS TE Components (1) • Link state IGP protocols enhanced to advertise “unreserved capacity” per link • SPF computation enhanced to route a TE tunnel (Constraint based Routing): • first prune the links which do not satisfy a constraint from the topology • Pick shortest path on the remaining topology Cisco Systems

31. MPLS TE Components (2) • Tunnel set-up (ie label binding) along the route computed by Constraint Base Routing: • via RSVP with extensions (eg Explicit Route Object), Note: RSVP state applies to a large aggregate of flows (i.e. a tunnel), rather than to a single flow or • via CR-LDP (ie extensions over LDP such as Explicit Route TLV) Cisco Systems

32. MPLS TE Components (3) • MPLS LFIB handles the forwarding “as usual” • only LFIB has been populated by another Control module than Destination Based LDP) • IGP enhanced on tunnel Head-ends to “route” IP packets “into” TE tunnels Cisco Systems

33. Traffic Engineering Summary • Connection-like aspects of MPLS allow traffic engineering for IP • Addresses limitations of connectionless routing • Avoids drawbacks of overlay (L2/L3) model • Combination with constraint-based routing provides automatic tunnel setup which maximises usage of existing resources and re-optimization on topology change • Underlying mechanism to achieve IP QoS more efficiently • In core, uses unmodified label switching Forwarding component Cisco Systems

34. Agenda • Label Switching Technology Overview • History & Motivation • Destination-Based Routing • Label Distribution Protocol(s) • Encapsulation • MPLS Over ATM • Applications • Quality of Service • Traffic Engineering • VPNs • Conclusion: Gbit Routing or MPLS? Cisco Systems

35. Scalability issues of Layer 2 VPNs • Complexity of provisioning n2 VCs per VPN, along with QOS for each VC • Complexity of designing routing system for each VPN over full VC mesh • Poor routing performance over mesh of adjacencies • Poor bandwidth efficiency if mesh is not used Cisco Systems

36. Why MPLS VPNs? • MPLS combines L3 routing and L2 forwarding • L3 routing provides • improved scalability by eliminating mesh of connections from CPE-to-CPE • L2 (label-based) forwarding provides • comparable security to L2 approaches • hiding of non-registered addresses • Hierarchical labels (label stack) further enhance scalability Cisco Systems

37. VPN - example VPN A/Site 2 VPN B/Site 1 CEA2 CE1B1 CEB2 VPN B/Site 2 P1 PE2 CE2B1 MPLS P2 PE1 PE3 CEA3 CEA1 P3 CEB3 VPN A/Site 3 VPN A/Site 1 VPN B/Site 3 Cisco Systems

38. Basic ingredients: • Constrained distribution of routing information w/ BGP • VPN-IP addresses • Multiprotocol Label Switching (MPLS) • in backbone, LFIB Forwarding “as usual” • Peer Model Cisco Systems

39. VPN - example VPN A/Site 2 VPN B/Site 1 CEA2 CE1B1 CEB2 VPN B/Site 2 P1 PE2 Single Routing Adjacency VPN<-->Cloud CE2B1 iBGP (VPN-IPv4 @) MPLS P2 PE1 PE3 LDP CEA3 Two-level labelled packets CEA1 CEB3 VPN A/Site 3 VPN A/Site 1 VPN B/Site 3 Cisco Systems

40. Agenda • Label Switching Technology Overview • History & Motivation • Destination-Based Routing • Label Distribution Protocol(s) • Encapsulation • MPLS Over ATM • Applications • Quality of Service • Traffic Engineering • VPNs • Conclusion: Gbit Routing or MPLS? Cisco Systems

41. A Perception Problem • A lot of people think label switching is all about forwarding performance • ATM switches used to be faster than routers • Plenty of label switching marketing reinforced this • This causes Gbit router implementors to say `Ha! Label Switching is useless’ as routers catch up • If standard IP forwarding at Gbit speeds is the only requirement, Gbit routers are the solution Cisco Systems

42. The value of label switching • Label switching adds value to Gbit routers • Traffic engineering support • VPNs • Ease of evolution • Label switching enables better IP/ATM integration • only relevant if ATM core was chosen for some reason, e.g. service integration • Not too hard to add label switching to Gbit routers Cisco Systems

43. References • Diffserv • RFC 2474. Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers. K. Nichols et al. • RFC 2475. An Architecture for Differentiated Service. S. Blake et al. • MPLS Basics • draft-ietf-mpls-arch-04.txt • draft-ietf-mpls-atm-01.txt • draft-ietf-mpls-ldp-03.txt • MPLS Traffic Engineering & DiffServ • draft-ietf-mpls-rsvp-lsp-tunnel-02.txt • draft-ietf-mpls-traffic-eng-00.txt • draft-ietf-mpls-cr-ldp-01.txt • draft-ietf-mpls-diff-ext-00.txt • draft-davari-mpls-diff-ppp-00.txt • MPLS VPNs • RFC 2547. BGP/MPLS VPNs. E. Rosen, Y. Rekhter. March 1999. Cisco Systems

44. References • Gigabit routers • Partridge et al. “A 50-Gb/s IP router," IEEE/ACM Transactions on Networking, vol. 6, June 1998. • Fast Routing Lookups • Brodnik et al. “Small Forwarding Tables for Fast Routing Lookups”, Sigcomm ‘97. • Waldvogel et al. “Scalable High Speed IP Routing Lookups”, Sigcomm ‘97. • Srinivasan et al. “Fast Scalable Level 4 Switching”, Sigcomm '98. • Lakshman and Stiliadis, "High Speed Policy Based-Packet forwarding...", Sigcomm '98. • MPLS • Davie et al. “Switching in IP Networks”, Morgan Kaufmann Publishers, May 1998. • Rekhter et al. “Tag Switching Architecture Overview”, IEEE Proceedings, vol 85, No. 12, Dec 1997. Cisco Systems