MPLS Multi-protocol label switching Mario Baldi Politecnico di Torino (Technical University of Torino)

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1 MPLS Multi-protocol label switching Mario Baldi Politecnico di Torino (Technical University of Torino) MPLS - 1

2 From MPLS Forum Documents MPLS is the enabling technology for the New Broadband (IP) Public Network MPLS - 3

3 The onion that makes telecos cry IP over ATM IP Leased Line Frame Relay ATM Circuit Emulation Optical switching IP over DWDM IP over Frame Relay MPLS - 4 IP over SONET/SDH IP over ATM Circuit Emulation

4 The future: WDM, IP, MPLS IP router with LAN or WAN interface IP IP router with T3 interface PABX with T1 interface IP router with LAN (GE) or WAN (PoS) Interface Optical switching IP/MPLS MPLS - 5

5 The idea Label IP packet Forwarding packets according to a label Instead of the IP destination address MPLS - 6

6 Why? Faster lookup The label may be used as an index Instead of longest prefix matching Traffic engineering MPLS - 7

7 MPLS introduces a connection-oriented paradigm in IP networks MPLS - 8

8 Network architecture MPLS network MPLS cloud Label switch router (LSR) Label edge router Ingress/egress LSR MPLS - 9

9 Label Switched Path (LSP) Ingress LSR A.k.a LSP tunnel Egress LSR MPLS - 1

10 Label switching A D X 1 2 D In Out Forwarding table In Out In Out In Out 1 1 D D MPLS - 11

11 MPLS key elements MPLS header Contains the label Protocols for label distribution Signaling Enhanced routing protocols Constraints in choosing paths MPLS - 12

12 MPLS history Tag Switching IP over ATM No problems with resolution of addresses Simpler signaling Only one control plan ATM with IP Reusing ATM switching hardware MPLS - 13

13 MPLS history MPλS (Multi-Protocol Lambda Switching) G-MPLS (Generalized MPLS) Packet switching Cell switching Circuit switching (SONET/SDH) Lambda switching Anything switching Unifying control plane MPLS - 14

14 MPLS header MPLS - 15

15 Shim header MPLS header Level 2 IP packet 2 bit 3 bit 1 8 bit Label Exp S TTL Exp: Experimental bits (CoS) S: Bottom of stack TTL: Time to live MPLS - 16

16 ATM and frame relay Connection oriented layer 2 protocols MPLS labels in layer 2 header VCI/VPI (ATM) DLCI (Frame relay) MPLS - 17

17 LSP setup: label and path selection A glimpse into the control plane MPLS - 18

18 Forwarding equivalence class (FEC) Packets that Are treated the same way by each LSR Follow the same path in MPLS network Receive the same label MPLS - 19

19 Three Key Actions Label binding Label mapping Label distribution Taken by LSRs MPLS - 2

20 MPLS - 21 Label Binding An LSR determines the label that should be prepended to packets belonging to a given FEC Downstream binding LSR on receiving end of a link Packets of the FEC shall be received with chosen label Upstream node to be notified Unsolicited On-demand

21 Label Mapping Association between Chosen by the considered LSR Input label Output label Chosen by downstream LSR Output port/next hop Based on routing How can the LSR know it? Actual creation of an LSP MPLS - 22

22 Label Distribution Notification of the label chosen for a given FEC Follows label binding An LSR that has made a binding, distributes it to neighboring LSRs Or at least to the upstream one MPLS - 23

23 Putting it all together: Sample LSP Setup A B X 1 2 for D 1 4 In 3 Out In Label for destination D Out Label for destination D In Out In Out 1 1 D MPLS - 26

24 Distribution Putting it all together: Sample LSP Setup A B X 1 2 for D 1 4 In 3 Label for destination D Out In In Out 1 Label for destination D Out In Out 1 Binding 1 D MPLS - 27

25 Static label binding (and mapping) Through management Equivalent to PVC ATM Non-scalable No interoperability among managing systems Impossible to have LSPs through different networks MPLS - 28

26 Dynamic Label Binding Data/traffic driven Triggered by data packets Control driven Triggered by control message Signaling MPLS - 29 Routing

27 Control Driven Label Binding Topology based The creation of LSPs is linked to the discovery of routes towards destinations Explicit creation of LSPs Explicit signaling Initiated by label edge routers MPLS - 3

28 Label distribution protocols Three alternatives (incompatible) Routing protocol: BGP Only topology based Label distribution protocol (LDP) Designed for the purpose Resource reservation protocol (RSVP) Designed for allocation in integrated service networks MPLS - 31

29 Routing protocols Used to determine LSP routing Impact label mapping phase Indirectly determine packet routing MPLS - 32

30 Routing protocols Existing protocols OSPF IS-IS BGP-4 carry topological information In MPLS context they are enhanced to... MPLS - 33

31 Routing protocols...carry information to constraint routing decisions (constraint data) Capacity of links Link utilization Dependencies among links Used for fault recovery MPLS - 34

32 Enhanced routing protocols Constraint based routing is fundamental to support traffic engineering OSPF TE IS-IS TE MPLS - 35

33 Hop-by-hop Routing Each LSR decides the next LSR of the LSP path E.g., Based on IP routing table Same principle and outcome (route) as in traditional IP routing MPLS - 36

34 Hop-by-hop Routing Procedure Pick label for upstream link Label binding Map it to Next hop Address of connected interface of next LSR Label announced by next LSR MPLS - 37

35 Hop-by-hop Routing Example A B X 1 2 Routing table X 3 D In 3 Out Routing table A 3 D In In Out 1 Label for destination D Out Label for destination D In Out Label for destination D 1 D MPLS - 4

36 Explicit constraint based routing A single switch chooses the path of a whole LSP For example, ingress LSR Explicit routing The choice is constraint based Constraint based routing MPLS - 41

37 Constraint Based Routing Distributed operation impossible No unique route selection criteria Conflicting constraints Hard to maintain constraint information synchronized It changes more frequently than topology information MPLS - 42

38 Label distribution protocols CR-LDP Constraint-based routing LDP RSVP-TE Should be modified RSVP for Traffic Engineering To be used with OSPF-TE and IS-IS-TE MPLS - 43

39 New possibilities Traffic engineering Guaranteed quality of service Not yet supported Per-class traffic engineering Synergy with DiffServ Fast fault recovery In less than 5 ms MPLS - 44

40 Traffic Engineering Motivation and enablement MPLS - 45

41 Traditional IP routing Aggregation! Traffic for D on optimal path D MPLS - 46

42 Traditional IP routing Congestion! Traffic for D on optimal path 4 overloaded links D MPLS - 47

43 Traditional IP routing Underutilization! Traffic for D on optimal path 4 overloaded links 9 underutilized links D MPLS - 48

44 Traffic Engineering Enables traffic distribution D MPLS - 49

45 Traffic Engineering No congestion Uniform use D MPLS - 5

46 Can you do it with traditional IP routing? Traffic for D on optimal path 4 overloaded links 9 underutilized links D MPLS - 51

47 Control plane and data plane Control plane OSPF R IP RIP IGRP o u t Continuous updating IS-IS Data plane BGP Routing database Routing table e MPLS - 52

48 It would be possible to choose paths according to load Traffic for D on optimal path overloaded links underutilized links D MPLS - 53

49 In such way, unloaded links are loaded and viceversa... Traffic for D on optimal path overloaded links underutilized links D MPLS - 54

50 ... and routing tables change... Traffic for D on optimal path overloaded links underutilized links D MPLS - 55

51 so does the link load... Traffic for D on optimal path overloaded links underutilized links D MPLS - 56

52 ... and the paths change again!!! Instability! Traffic for D on optimal path overloaded links underutilized links D MPLS - 57

53 Control plane and data plane L Signaling (LSP setup) LDP RSVP Routing table Control plane RIP OSPF MPLS IS-IS IGRP BGP S R LSP setup Data plane Forwarding table Routing database MPLS - 58

54 Traffic Engineering with MPLS D MPLS - 62

55 Traffic Engineering without MPLS ATM has so far been used for traffic engineering on IP networks Two control plans Routers are ATM-unaware Great number of adjacencies Limitated scalability MPLS - 63

56 Traffic Engineering with MPLS MPLS is IP-aware Only one control plan operating on physical topology Simpler Greater scalability MPLS - 64

57 MPLS extensions MPλS (MPLambdaS) MPLS control plans in optical networks GMPLS (Generalized MPLS) MPLS control plane in any network MPLS - 65 Packet, circuit, optics, etc

58 Adding CoS and QoS Resources and service modes may be associated to a FEC at LSP setup Explicit support is required in LSR data plan and control plan MPLS - 66

59 Class of service (CoS) MPLS - 67 Relative priority among different FECs It does offer absolute guaranties Support of DiffServ model Per-hop behavior EF (expedite forwarding), AF (assured forwarding) Per class traffic engineering DS-aware traffic engineering

60 Quality of service (QoS) Specific guaranties on Bandwidth Delay Burst size MPLS - 68

61 Advantages of QoS in MPLS Unified network supporting all types of services (marketing message) Support of QoS and real-time services on IP (e.g., voice) is not ready A lot of multi-service networks now have a paradigm Ships-in-the-night ATM protocols are ATM typical services MPLS control plan for IP services MPLS - 69

62 Fast Fault Recovery LSP Re-routing node Re-routing node Link re-routing Edge-to-edge re-routing MPLS - 72

63 Label Stack hierarchy and scalability Header Layer 2 Label 3 Label 2 Label 1 IP packet MPLS Domain 1 Routing table reduction Forwarding table reduction MPLS Domain 2 MPLS Domain 3 MPLS - 73

64 MPLS and scalability MPLS labels introduce hierarchy Various hierarchical levels, as needed for the necessary scalability Routing tables of transit routers do not have to be comprehensive LSP between edge routers (Simpler and faster exact match of labels rather than longest prefix matching) MPLS - 74

65 Penultimate Hop Popping (PHP) MPLS - 75 The last but one node on the path of an LSP pops the label The LER routes the packet based on IP address (or next label in stack) Distribution of label 3 indicates (implicit) PHP Explicit PHP: label is swapped When shim header is needed E.g., EXP bits

66 VPN: Virtual Private Network Services similar to those of a private network, but provided on a public infrastructure (IP) Privacy and security Overlapping addressing spaces (private) Non-unique addresses MPLS - 76 Class of Service (CoS) and Quality of Service (QoS)

67 VPN based on MPLS Labels hide IP addresses of users on the public network Allow for ovelapping address spaces Service flexibility FEC MPLS - 77

68 VPN based on MPLS MPLS allows a scalable solution for VPN services Other approaches require explicit setting (manual) of tunnels between each pair of websites Number of VPNs Number of VPN members MPLS - 78

69 Standardization IETF Internet Engineering Task Force MPLS working group FR/MPLS Alliance Consortium of vendors Foster deployment Aspects omitted by IETF VoMPLS, ADSL MPLS - 79