MPLS (Multi-Protocol Label Switching)

1. MPLS (Multi-Protocol Label Switching) Eric Donnelly EEL6785 6/19/03

2. Overview • Background • History • Components, Definitions • Operation • Performance Measurements • Summary

3. Background • Standard being developed by IETF (Internet Engineering Task Force) since 1997 • Integrates key features of Layer 2 and 3 technologies w/o limitation to a particular protocol • Packets labeled and sent through network on paths rather than hop-to-hop as in IP datagrams Courtesy of [4]

4. Control: Control: Control: IP Router Software IP Router Software ATM Forum Software Forwarding: Forwarding: Forwarding: Longest-match Lookup Label Swapping Label Swapping Basic Idea • MPLS is a hybrid model adopted by IETF to incorporate best properties in both packet routing & circuit switching MPLS ATM Switch IP Router Courtesy of [1]

5. What about GMPLS? • GMPLS (Generalized Multi-Protocol Label Switching) • Previously Multi-Protocol Lambda Switching (another MPLS) • GMPLS is deployed from MPLS (Label) Apply MPLS control plane techniques to optical switches and IP routing algorithms to manage lightpaths in an optical network • We will focus on MPLS in this presentation

6. History • In Mid-90s, many ISPs migrated from router based cores to IP-over-ATM, this provided: • Greater Bandwidth • Deterministic forwarding performance • Traffic engineering support Courtesy of [4]

7. History (Cont.) • No specific Internet backbone networking equipment available for ISPs. • Equipment needed to be adapted—ATM best solution at time • However, Continued Internet growth increased stress on ATM networks: • Bandwidth limitations • 20 percent “cell tax” • Designed for different tasks (IP—conncectionless, ATM—connection-oriented) • Late 1996, proprietary multilayer solutions emerged with integrated ATM switching and IP routing: • IP Switching—Ipsilon/Nokia • Tag Switching—Cisco Systems • Aggregate Route-Based IP Switching (ARIS)—IBM • IP Navigator—Cascade/Ascend/Lucent Technologies • Cell Switching Router (CSR)—Toshiba --These were all similar technologies, but were NOT interoperable

8. History (Cont.) • Each multilayer switch ran standard IP routing software (OSPF, BGP-4) • Different label binding approaches • Data-driven model • Label bindings created when data packets arrive. • Labels created either when first packet in a flow or after a number of packets in a flow have arrived. • IP Switching and CSR used this technique. • Control-driven model • Label bindings created when control information arrives. • Assigned in response to processing of protocol traffic, control traffic (such as RSVP), or static configuration. --Control-driven model used in MPLS! Note: OSPF-Open Shortest-Path First BGP-Border Gateway Protocol RSVP-Resource Reservation Protocol

9. MPLS emerges • IETF creates MPLS working group to create unified standard able to operate on any media infrastructures (Frame Relay, PPP, SONET), not just ATM. • Uses Control-driven model. • Defines new standard-based IP signaling and label distribution protocols, as well as existing protocol extensions (this supports multivendor interoperability). • Does not implement any of the ATM forum signaling or routing protocols (eliminates coordinating of 2 protocol architectures).

10. Terminology/Components • FEC (Forwarding Equivalence Class)-Group of packets sharing the same type of transport. • LSR (Label Switched Router)-Swaps labels on packets in core of network. • LER (Label Edge Router)-Attach Labels to packets based on a FEC. • LSP (Label Switch Path)-Path through network based on a FEC (simplex in nature). • LIB (Label Information Base)- MPLS equivalent to IP routing table, contains FEC-to-Label bindings.

11. 1a. Routing protocols (e.g. OSPF-TE, IS-IS-TE) exchange reachability to destination networks 4. LER at egress removes label and delivers packet 1b. Label Distribution Protocol (LDP) establishes label mappings to destination network 10 20 40 IP IP IP IP IP 2. Ingress LER receives packet and “label”s packets 3. LSR forwards packets using label swapping MPLS Operation Courtesy of [1]

12. FECs- Group of packets sharing the same type of transport • All packets in such a group are provided the same treatment en route to the destination. Can be partitioned by: • Source-to-Destination Address • Application • Bandwidth Requirement • Conventional Routing=>packet assigned to FEC at each hop (Layer 3 lookup). • MPLS=>done only once (at egress). [9]

13. LSRs and LERs • The devices used for MPLS can be classified into label edge routers (LERs) and label switching routers (LSRs). • A LSR is a high-speed router device in the core of an MPLS network. • Participates in the establishment of LSPs, using the appropriate label signaling protocol • Does high-speed switching of the data traffic based on the established paths. • A LER is a device that operates at the edge of the access network and MPLS network. • Supports multiple ports connected to dissimilar networks (such as frame relay, ATM, and Ethernet) • Forwards this traffic on to the MPLS network after establishing LSPs, using the label signaling protocol at the ingress and distributing the traffic back to the access networks at the egress. • Plays important role in the assignment and removal of labels, as traffic enters or exits an MPLS network.

14. Inside a LSR • Data Plane • Control Plane NHLFE LIB FEC DATA Figures Courtesy of [10]

15. Labels • The MPLS forwarding component is based on the label-swapping algorithm. • Label encapsulated in MPLS header, which is “sandwiched” between the Layer 2 and IP header. • If Layer 2 technology supports labels (ATM VPI/VCI, Frame Relay DLCI), MPLS label and header encapsulated in the Layer 2 label field.

16. Why Label Swap? • Label swapping provides a significant number of operational benefits when compared to conventional hop-by-hop network layer routing. • Gives an ISP flexibility in the way that it assigns packets to FECs. • Destination address (like conventional IP routing) • Source address. • Application type. • Point of entry/exit to/from the label-swapping network. • CoS conveyed in the packet header. • Any combination of the above. • ISPs can construct customized LSPs that support specific application requirements (for instance, VPNs). LSPs can be designed to: • minimize the number of hops • bandwidth requirements • bypass points of congestion • Offer ISPs precise control over the flow of traffic in their networks.

17. …For Instance • If network core runs conventional longest-match IP forwarding: • Data from Host A and B follow path 1 since it is the shortest-path computed. • With MPLS, network administrator could split traffic: • Host A traffic over path 1 • Host B traffic over path 2 Courtesy of [4]

18. MPLS header • Label field- Actual MPLS label (20bits). • CoS field- “Class of Service” can effect queuing and discard algorithms applied to packets (3 bits). • S (Stack) field- supports a hierarchical label stack (1 bit). • TTL field- “Time-to-live” provides conventional IP TTL functionality (8 bits). Courtesy of [4]

19. …In ATM …Frame Relay …PPP/Ethernet Figures Courtesy of [5]

20. Label Creation • topology-based method—uses normal processing of routing protocols (such as OSPF and BGP) • request-based method—uses processing of request-based control traffic (such as RSVP) Note: OSPF-Open shortest-path first BGP- Border Gateway Protocol

21. Label Spaces • Labels used by an LSR for FEC-label bindings are split into 2 categories: • Per platform-label values are unique across an entire LSR. • Per interface-label values are associated w/ interfaces. Label values provided on different interfaces could be the same.

22. Label Distribution • No single method of signaling required • Enhancements of existing routing protocols (to allow piggybacking of label information) include: • Border Gateway Protocol (BGP) • Resource Reservation Protocol (RSVP) • LDP (Label Distribution Protocol)- Defined by IETF for signaling and management of label space. --Extensions have been defined to support explicit routing based on QoS and CoS requirements.

23. Label Distribution schemes • LDP—maps unicast IP destinations into labels • RSVP, CR–LDP—used for traffic engineering and resource reservation • BGP—external labels (VPN)

24. Signaling Mechanisms (general) • label request—An LSR requests a label from its downstream neighbor so that it can bind to a specific FEC. This mechanism can be employed down the chain of LSRs up until the egress LER (i.e., the point at which the packet exits the MPLS domain). • label mapping—In response to a label request, a downstream LSR will send a label to the upstream initiator using the label mapping mechanism. Courtesy of [5]

25. Distribution and Signaling Protocols • Implicit routing- labels are set-up and torn-down (like telephone calls), also known as hard state. • Explicit routing- allows for better traffic engineering, traffic tunnels are created based on overall view of topology. More dynamic. Courtesy of [10]

26. Label Distribution Protocol (LDP) • Four message classes • Discovery-Announce and maintain presence of an LSR. • Session-establish, maintain, terminate sessions b/w LDP peers. • Advertisement-create, change, delete label mappings. • Notification-advisory and error info. [9] • Discovery: Runs over UDP • All others run over TCP

27. Message Structure • All LDP messages have a common message structure (Type-Length-Value encoding scheme) [11] • Type: Type of message For specifics on this frame see http://www.networksorcery.com/enp/protocol/LabelDistributionProtocol.htm#Glossary

28. Discovery • LSR multicasts HELLO message to well-known UDP port on “all routers on this subnet” multicast group. • All routers listen to this group to learn all LSRs with direct connection. • When an LSR is detected, a TCP LDP connection is established. The HELLO message can also be sent to a well-known UDP port at the IP address of a router if the IP address is known through static configuration.

29. Some Important Messages • INITIALIZATION- label allocation mode, timer values, range of labels to be used • KEEPALIVE- respond to Initialization of parameters are acceptable. Connection is terminated if timely keepalives are not received • LABEL MAPPING – Advertise a binding between address prefix and label • LABEL WITHDRAWEL – reverse LABEL MAPPING, can occur because of routing changes • LABEL RELEASE– Used in Conservative Label Retention mode • LABEL REQUEST– Used for down-stream-on-demand mode to request label mapping • LABEL REQUEST ABORT – If next hop changes so that the prior label request is invalid, this cancels the previous request

30. Slide courtesy of [9]

31. Performance Measurements • Computers: Pentium II 300 • 128 MB RAM • Fast Ethernet • FreeBSD 4.1 • LERs and LSRs:Juniper Networks M40TM routers (MPLS and RSVP-TE). • Interconnect:OC-12 (ATM 80 Mbps ATM (PVC) connections for experiment.) • Physical distance: • LSR 1-LSR 3, LSR 2 -LSR 3 =40km • LSR 1-LSR 2 =5km Courtesy of [8]

32. Results Path from A to C (TCP stream) Throughput of both MPLS paths (TCP streams) Courtesy of [8]

33. Results Latency from A to C for TCP stream Latency from A to C for UDP stream Courtesy of [8]

34. Summary • Improves packet-forwarding performance in the network • MPLS enhances and simplifies packet forwarding through routers using Layer-2 switching paradigms. • MPLS is simple, which allows for easy implementation. • MPLS increases network performance because it enables routing by switching at wireline speeds. • Supports QoS and CoS for service differentiation • MPLS uses traffic-engineered path setup and helps achieve service-level guarantees. • MPLS incorporates provisions for constraint-based and explicit path setup. • Supports network scalability • MPLS can be used to avoid the N2 overlay problem associated with meshed IP–ATM networks. • Integrates IP and ATM in the network • MPLS provides a bridge between access IP and core ATM. • MPLS can reuse existing router/ATM switch hardware, effectively joining the two disparate networks. • Builds interoperable networks • MPLS is a standards-based solution that achieves synergy between IP and ATM networks. • MPLS facilitates IP–over-synchronous optical network (SONET) integration in optical switching. • MPLS helps build scalable VPNs with traffic-engineering capability.

35. …However • Some Internet Purists complain that MPLS breaks some critical Internet architectural principles: • MPLS supports tunneling, which breaks the transparency paradigm. • MPLS supports sessions, it breaks the datagram model. • But MPLS provides great value to ISPs, such as lower operating costs and ability to provide QoS to businesses.

36. Questions???

37. References • Yin, Li, PowerPoint Presentation: “MPLS and GMPLS,” University of California, Berkeley, Summer 2002. • R. Ramaswami and K. N. Sivarajan, Optical Networks: A Practical Perspective 2nd Ed., Morgan Kaufmann Publishers. • Nortel Networks, “MPLS—An introduction to multiprotocol label switching,” 2001, http://www.nortelnetworks.com/corporate/technology/mpls/collateral/55053.25-04-01.pdf. • Semeria, Chuck, Juniper Networks, “Multiprotocol Label Switching: Enhancing Routing in the New Public Network,” 2000. • International Engineering Consortium, “Multiprotocol Label Switching (MPLS),” 2003, http://www.iec.org/online/tutorials/mpls/ • Farkas, K. et al. “IP Traffic Engineering of OMP Technique,” Technical University of Budapest, Hungary, 2000. • Johnson, J., “Despite criticism, MPLS is here to stay,” Network World, April 2002. http://www.nwfusion.com/columnists/2002/0408eye.html • Bayle, T. et al. “Performance Measurements of MPLS Traffic Engineering and QoS,” Hiroshima University, http://www.isoc.org/isoc/conferences/inet/01/CD_proceedings/T43/ . • Nortel Networks, “MPLS Tutorial,” May, 1999, http://www.nanog.org/mtg-9905/ppt/mpls/ . • Gallaher, R, “Advanced MPLS Signaling,” December 2001, http://www.convergedigest.com/tutorials/mpls3/page1.htm . • Network Sorcery Inc., “LDP,” http://www.networksorcery.com/enp/protocol/LabelDistributionProtocol.htm#Glossary .

38. Lines studied in simulation Simulation (EXTRA) Courtesy of [6]

39. Results (EXTRA) MPLS Simulation OSPF Simulation Courtesy of [6]

40. Results (EXTRA) These simulations were done using an OMP (Optimized Multipath) extension to their existing protocols. OSPF-OMP MPLS-OMP Courtesy of [6]

41. History (Extra) • Control-driven model benefits • Labels are assigned and distributed before arrival of data traffic. This means that if a route exists in the IP forwarding table, a label has already been allocated for the route, so traffic arriving at a multilayer switch can be label swapped immediately. • Scalability is significantly better than in the data-driven model. Number of label switched paths proportional to the number of entries in the IP forwarding table, not to the number of individual traffic flows. Label assignment based on prefixes, rather than individual flows, permits a single label to represent a highly aggregated FEC. • In a stable topology, the label assignment and distribution overhead is lower than in the data-driven model because label-switched paths are established only after a topology change or the arrival of control traffic, not with the arrival of each “new” traffic flow. • Every packet in a flow is label switched, not just the tail-end of the flow as in the data-driven model.