Multi-Protocol Label Switch (MPLS) 1

Outline Introduction MPLS Terminology MPLS Operation – Label Encapsulation Label Distribution Protocol (LDP) Any Transport Service over MPLS MPLS Applications – Traffic Engineering – MPLS-based VPN – MPLS and QoS Summary 2

Why MPLS? Growth and evolution of the Internet The need for network convergence to support both voice and data services on both carrier and enterprise networks The need for advanced and guaranteed service over the Internet – The need of virtual circuit but without the complexity of provisioning and managing virtual circuits. PVC: too much provisioning and management work SVC: [signaling] too complex to support and trouble shoot The need for an efficient transport mechanism – routing: flexibility – forwarding: price/performance – Can we forward IP packets? Answer: MPLS 3 Performance and service of Layer-2 and management of layer-3

Motivation for Carriers Network convergence – Single network to support voice and data traffic Ease of network management – to provision new services – to support various Service Level Agreements (SLA) Ease of Traffic Engineering – To reroute during node failures or network congestion 4

Motivation for Enterprises Network convergence – Single network for voice and data A meshed topology (any-to-any) without the nightmare of cost and management – Confusion with too many Frame Relay PVCs Quality of Service (QoS) for intranet – Ease of bandwidth management – Flexibility of bandwidth provisioning 5

MPLS History IP over ATM IP Switching by Ipsilon Cell Switching Router (CSR) by Toshiba Tag switching by Cisco Aggregate Route-based IP Switching (IBM) IETF – MPLS – – RFC3031 – MPLS Architecture – RFC2702 – Requirements for TE over MPLS – RFC3036 – LDP Specification – over 113 RFCs related to MPLS 6

MPLS and OSI (MPLS is a layer 2.5 protocol) 7 Physical IP Applications TCP UDP PPPFR ATM MPLS When a layer is added, no modification is needed on the existing layers. Ethernet DWDM MPS

MPLS and OSI (MPLS is a layer 2.5 protocol) 8

Label Switching (This is not new!) ATM: VPI/VCI Frame Relay: DLCI X.25: LCI (logical Channel Identifier) TDM: the time slot (Circuit Identification Code) Ethernet switching: MAC Address 9

Label Substitution (swapping) 10 Label-A1 Label-B1 Label-A2 Label-A3 Label-A4 Label-B2 Label-B3 Label-B4

MPLS A protocol to establish an end-to-end path from source to the destination A hop-by-hop forwarding mechanism Use labels to set up the path – Require a protocol to set up the labels along the path Support multi-level label transport It builds a connection-oriented service on the IP network – Note: ATM and Frame Relay also support connection- oriented services, but IP does not. 11

Terminology LSR - Routers that support MPLS are called Label Switch Router LER - LSR at the edge of the network is called Label Edge Router (a.k.a Edge LSR) – Ingress LER is responsible for adding labels to unlabeled IP packets. – Egress LER is responsible for removing the labels. Label Switch Path (LSP) – the path defined by the labels through LSRs between two LERs. Label Forwarding Information Base (LFIB) – a forwarding table (mapping) between labels to outgoing interfaces. Forward Equivalent Class (FEC) – All IP packets follow the same path on the MPLS network and receive the same treatment at each node. 12

How does it work? 13 IP #L1IP#L2IP#L3 IP LSR LER IP Routing IP Routing Label Switching Label Switching Add label at the ingress LER remove label at the egress LER

MPLS Operation 14 Label Path: R1 => R2 => R3 => R4

Label Forwarding Information Base (LFIB) RouterIncoming Label Incoming Interface Destination Network (FEC) Outgoing Interface Outgoing Label R1---E S16 R26S S211 R311S S37 R47S E Note: the label switch path is unidirectional. Q: create LFIB for R4 => R3 => R2 => R1

Label Encapsulation Label information can be carried in a packet in a variety of ways: A small, shim label header inserted between the Layer 2 and network layer headers. As part of the Layer 2 header, if the Layer 2 header provides adequate semantics (such as ATM). As part of the network layer header (future, such as IPv6). In general, MPLS can be implemented over any media type, including point-to-point, Ethernet, Frame Relay, and ATM links. The label-forwarding component is independent of the network layer protocol. 16

17 Shim Header The Label (Shim Header) is represented as a sequence of Label stack entries Each Label is 4 bytes (32 bits) 20 Bits is reserved for the Label Identifier Label Identifier (20 bits) Exp (3 bits) S (1 bit) TTL (8bits) Label Identifier : Label value (0 to 15 are reserved) Exp : Experimental Use S : Bottom of Stack (set to 1 for the last entry in the label) TTL : Time To Live

MPLS and TTL TTL: Time to Live In IP, TTL is used to prevent packets to travel indefinitely in the network. MPLS uses the same mechanism as IP. Why do we need TTL? – MPLS may interwork with non-MPLS network. TTL is in the label header of PPP and Ethernet (shim header) Not supported in ATM. 18

19 Ingress LabelFECEgress Label /249 When an unlabeled packet arrives at an ingress router, a label has to be applied. A packet can be mapped to a particular FEC based on the following criteria: destination IP address source IP address TCP/UDP port class of service (CoS) or type of service (ToS) application used any combination of the previous criteria. Forward Equivalent Class (FEC) Classification

Label Distribution Protocol (LDP) Labels are distributed between LERs and LSRs using LDP LSRs regularly exchange label and reachability information with each other using standardized procedures Used to build a picture of the network that can be used to forward packets Label Switch Paths are created by network operators – similar to PVC and VPN 20

MPLS over ATM/Frame Relay/Ethernet A majority of MPLS examples are used to carry IP traffic over Ethernet links But MPLS can also carry IP traffic over ATM and frame relay links 21

MPLS and ATM Most carriers’ backbone are ATM- based. What is the process of migrating from ATM to MPLS-based backbone? 22

MPLS and ATM The label information of MPLS can be carried in the ATM VCI field. If two levels of labeling are needed, then the ATM VPI field could be used. The VCI field, however, is adequate for most applications. Implementing MPLS on an ATM switch would simplify integration of ATM switches and routers. An ATM switch capable of MPLS would appear as a router to an adjacent router. This approach avoids the issues of ATM addressing, routing, and signaling schemes. Implementing MPLS on an ATM switch does not preclude the capability to support a traditional ATM control plane (such as PNNI) on the same switch. The two components, MPLS and the ATM control plane, would operate independently with VPI/VCI space and other resources partitioned so that the components would not interact. Two implementation schemes: VC-merging vs. non-merging 23

ATM LSR - Non-Merging (note: this is MPLS over ATM) IP Packet ATM cell Each ATM VC has its own MPLS label In/IntfIn/LabelDestinationOut/IntfOut/Label …………

25 ATM LSR - VC-Merging IP Packet ATM cell Multiple AMT VCs with the same destination and QoS are merged on the MPLS network with the same label In/IntfIn/LabelDestinationOut/IntfOut/Label …………

Frame Relay over MPLS Example 26 R1 R2 Ra Rb Rc Lo: loopback interface. Why is it needed? R1 and R2: legacy frame relay router Ra and Rb: Label Switch Edge Router. Label path is between Ra and Rb.

Frame Relay over MPLS (cont.) 27 IP RFC2427 Frame Relay PHY FR PHY RFC 4619 MPLS L2 PHY MPLS L2 PHY MPLS L2 PHY FR PHY RFC 4619 IP RFC2427 Frame Relay PHY IP lo: DLCI 514 DLCI 513 Note: The IP addresses for MPLS configuration and Frame Relay are on different IP subnets. lo:

MPLS Applications Traffic Engineering Virtual Private Network (VPN) Quality of Service (QoS) 28

Traffic Engineering Traffic engineering allows a network administrator to select the path between two notes and bypass the normal routed hop-by-hop paths. An administrator may elect to explicitly define the path between nodes to ensure QoS or have the traffic follow a specified path to avoid traffic congestion at certain hops. The network administrator can reduce congestion by forcing the frame to travel around the overloaded segments. Traffic engineering, then, enables an administrator to define a policy for forwarding frames rather than depending upon dynamic routing protocols. Traffic engineering is similar to source-routing in that an explicit path is defined for the frame to travel. However, unlike source-routing, the hop- by-hop definition is not carried with every frame. Rather, the hops are configured in the LSRs ahead of time along with the appropriate label values. The administrator could be a centrally located program. Traffic engineering is an important tool for network management. It is NOT a customer service. (So you will not see it on a carrier’s web site.) 29

30 MPLS – Traffic Engineering End-to-End forwarding decision determined by ingress node. Enables Traffic Engineering LER 1 LSR 2 LSR 3 LER 4 LIP Forward to LSR 2 LSR 3 LSR 4 LSR X Overload !! IP L L

MPLS-based VPN One of most popular MPLS applications is the implementation of VPN. The basic concept is the same as ATM transparent LAN. Using label (instead of IP address) to interconnect multiple sites over a carrier’s network. Each site has its own private IP address space. Different VPNs may use the same IP address space. 31

MPLS VPN - Example E1 10 E3 -- E2 20 E3 10E1 30 E2 20 E1 40 E2 30 E3 -- E1 40 E3 -- E2 E1 E2 E1 E2 -- E1 30 E3 -- E2 40 E3 30 E2 10 E1 40 E2 20 E1 10 E3 -- E1 20 E3 -- E1 LSP E3 E1 E2 E3 uni-direction

MPLS VPN Connection Model 33 VPN_A VPN_B VPN_A VPN_B VPN_A MPLS Core VPN_A: /24, /24, /24, /24 VPN_B: /24, /24, /24 Q: For a meshed connection, how many label paths are needed? MPLS Edge MPLS Edge

Case Study (I) AT&T MPLS Private Transport Network Services Features and Benefits Advanced Management options MPLS-based security Meshed topology for any-to-any connectivity Traffic prioritization - 4 Classes of Services (CoS) Service Level Agreements (SLAs) Web-based reporting 34

Case Study (II) Verizon Private IP Service (MPLS) History: MCI (Verizon) adopted MPLS on a large scale in 1998 as a traffic engineering technology on its public Internet backbone Features and Benefits: Exceptional Service. 24-hour monitoring customer service, and service level agreements (SLAs). Any-to-Any Connectivity. Multiple locations are connected (meshed topology). You no longer need PVCs to communicate between sites; rather Cost-Effective Solution. Private IP Service utilizes existing network infrastructure without building and operating a private VPN. Intranets and Extranets. Private IP Service captures the enhanced networking efficiencies associated with an IP-based WAN, bringing together all the elements to support e-business applications within the company or between companies. MPLS Technology. Private IP Service provides varying Class of Services (CoS) and flexible IP routing that optimize network’s performance. 35