Introduction to Multi-Protocol Label Switching (MPLS)

1. MPLS (MultiProtocol Labeling Switching) School of Electronics and Information Kyung Hee University. Choong Seon HONG <cshong@khu.ac.kr>

2. Introduction • Multi-protocol Label Switching • A switching and forwarding scheme • Evolved from Cisco’s Tag Switching • It located between Layer 2 and Layer 3 of the OSI reference model • It make use of the fixed length label (20-bit) for switching and forwarding

3. Introduction • Major components: • LERs (Label Edge Routers) • It located at the boundary of the MPLS network and its function is assignment and removal of labels as packet enter end leave the MPSL network respectively. • LSRs (Label Switching Routers) • It located at the core part of the MPLS network and its function perform packet switching based on the label.

4. Introduction • Major components (cont.) • LDP (Label Distribution Protocol) • Maps unicast IP address into MPLS labels • LSPs (Label-switched Paths) • A flow of MPLS packets with same label • Similar to VC (Virtual Circuit) in ATM network

5. Introduction • General operations: • label creation and distribution • table creation at each router • label-switched path creation • label insertion/table lookup • packet forwarding/switching • Label removal

6. Introduction • Applications: • Used in core network to improve packet forwarding performance • Support QoS and CoS application • Improve network scalability (use of LSPs) • Integrated IP and ATM network • IP-VPN

7. What is Multi-protocol Label Switching ?

8. MPLS Technology • Routers or switches that handle MPLS and IP are known as Label Switch Routers (LSR’s) • LSR’s at the edge of MPLS networks are sometimes referred to as Label Edge Routers (LER’s) • Ingress LER’s are responsible for classifying unlabelled IP packets and appending the appropriate label. • Egress LER’s are responsible for removing the label and forwarding the unlabelled IP packet towards its destination. • All IP packets that follow the same path through the MPLS network and receive the same treatment at each node are known as a Forwarding Equivalence Class (FEC).

9. Label Switching Devices Label Switching Routers (LSRs) (ATM Switch or Router) Label Edge Routers

10. MPLS Technology There are three key elements of MPLS • The MPLS header stack • Which contain the MPLS label on which Label Switch Routers will forward the packet. Headers can be stacked. • The enhanced IP routing protocols • Which distribute topology and constraint based data • The label distribution protocols • The standardized connection establishment protocols through which LSR’s set up a complete path from ingress LSR to egress LSR. This path is known as a Label Switched Path or LSP. MPLS adds a connection oriented paradigm into IP networks

11. MPLS Shim Header Structure MPLS Headers can be used “recursively” MPLS "shim" headers ... Layer 2 Header IP Packet Label: 20-bit value, (0-16 reserved) Exp.: 3-bits Experimental (ToS) S: 1-bit Bottom of stack : Stack Indicator TTL: 8-bits Time To Live Label Exp. S TTL 4 Octets Label Switching Look up inbound label + port (+Exp) to determine outbound label + port + treatment Header operations Swap (label) Push (a new header) Pop (a header from stack) MPLS encapsulations are also defined for ATM and Frame relay.

12. Establishing the label bindings • Each switch needs a table that contains the actions it is to perform when a given label arrives. • The downstream end of a link needs to know what label values will be sent. • This can be done by management action – directly equivalent to PVC’s in ATM. • But this does not scale well. • And there is no interoperability between management systems – so multi-operator connections are difficult if not impossible. • Hence trend to protocol driven service establishment and the reason for IP’s success. • So we need to automate the LSP establishment process.

13. MPLS Routing protocols Start with existing IGP’s • OSPF • IS-IS • BGP-4 • Enhance to carry constraint data • OSPF-TE • IS-IS –TE Distribute topology information only Constraint data Link capacity,Link utilization Resource class Priority Pre-emption etc Constraint based routing is the key to Traffic Engineering

14. Explicit constraint based routing Route determined by ingress LSR based on overall view of topology, and constraints Traffic engineering CoS and (QoS) fast (50ms) rerouting Label Distribution Protocols Hop by Hop routing Ensures routers agree on bindings between FEC’s and the labels. Label paths follow same route as conventional routed path • LDP • CR-LDP • RSVP-TE

15. MPLS Partitions Routing and Forwarding (1) Based on: Classful Addr. Prefix? Classless Addr. Prefix? Multicast Addr.? Port No.? ToS Field? Routing OSPF, IS-IS, BGP, RIP Forwarding Table Forwarding Based on: Exact Match on Fixed Length Label MPLS By separating Routing from forwarding MPLS introduces more flexibility to develop new routing solutions without impacting the data plane hardware of label switch routers Single forwarding paradigm – multiple routing paradigms The edge LSR is able to use a wide variety of input in determining the FEC, and not just the destination IP address Flexibility in forming FEC’s

16. MPLS Partitions Routing and Forwarding(2) • 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

17. 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

18. 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)

19. 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

20. 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

21. 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

22. Label Distribution for ATM Downstream 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

23. How does it fit into IP network development plans – MPLS Applications

24. Applications of MPLS • Traffic Engineering • Adding Class of Service (CoS) and Quality of Service (QoS) • Network scalability • Supporting IP VPN’s

25. Traffic EngineeringCurrent IGP’s lead to Hyper-Aggregation TRAFFIC FOR D SHORTEST PATH ROUTED D S MASSIVE CONGESTION CONGESTION

26. Traffic EngineeringCurrent IGP’s lead to Hyper-Aggregation TRAFFIC FOR D SHORTEST PATH ROUTED 9 UNDER ULTILIZED] 3 OVERUTILIZED ] LINKS D S MASSIVE CONGESTION CONGESTION

27. Traffic EngineeringIS the Answer • Objectives • Map actual traffic efficiently to available resources • Controlled use of resources • Redistribute traffic rapidly and effectively in response to changes in network topology - particularly as a consequence of line or equipment failure • Note this complements Network Engineering • Putting the network where the traffic is

28. Traffic engineering distributes traffic Traffic distributed over Network resources by MPLS traffic engineering - Congestion eliminated D S

29. Adding CoS and QoS • Explicit path set up can also associate specific resource requests with an FEC • Class of service • Establish relative priority of one FEC over another – no absolute guarantees • Quality of service • Specific guarantees on • Bandwidth • Delay • Burst size etc • Primary objective is for MPLS to support the Diff-Serv QoS model (EF, AF1-12,etc) CoS and QoS require explicit support in the data plane of the LSR’s

30. Hierarchy via Label stack= Network scalability Layer 2 Header Label 3 Label 2 Label 1 IP Packet Within each domain the IGP simply needs to allow the Boarder (ingress) routers to determine the appropriate egress boarder router Reducing drastically size of routing table in transit routers MPLS Domain 1 MPLS Domain 2 MPLS Domain 3

31. Benefit of MPLS in scaling • MPLS labels introduce hierarchy • Transit routers no longer need to handle complete routing tables • New layers of the hierarchy can be introduced as needed for scaling.

32. Support of IP VPN’s • A Virtual Private Network • An IP network delivering private network services over a public infrastructure • Supports global and non unique private address space • Supports CoS and QoS • Use of labels isolates IP addresses within public network from customer IP addresses • Creates a highly scalable VPN

33. Benefit of MPLS IP VPN’s • Provides a mechanism to scale both the number of VPN’s and the number of members per VPN to very large numbers. • Allows VPN’s to have non-unique IP addressing • Provides for a great deal of flexibility in defining the VPN service (from the mapping to FEC’s) • Enables meaningful CoS and QoS Service Level Agreements (SLA’s) to be associated with a VPN

34. 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