Table of Contents MPLS. ATM (Asynchronous Transfer Mode) IP Forwarding. Faster IP forwarding ATM and MPLS

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1 Table of Contents MPLS Multi Protocol Label Switching (an introduction) Faster IP forwarding ATM and MPLS Karst Koymans Informatics Institute University of Amsterdam (version 152, 2016/03/14 20:57:44) Tuesday, March 15, 2016 MPLS Operation Labels, paths and switching MPLS Control and Label Management MPLS Applications MPLS VPN techniques IP Forwarding ATM (Asynchronous Transfer Mode) Forwarding IP packets Normally done by destination IP address Routing protocols are used to distribute layer 3 information Decisions are made hop-by-hop independently Connectionless operation Routing protocol should offer consistency Shortcomings Routing tables may become very large Limited traffic engineering options Uses small fixed size cells to transport data Each cell contains 53 bytes A fixed size header of 5 bytes A fixed size payload of 48 bytes Often data needs to be fragmented Uses VCs (Virtual Circuits) between endpoints Switching based on labels An 8-bit (UNI) or 12-bit (NNI) Virtual Path Identifier (VPI) An 16-bit Virtual Channel Identifier (VCI) Switching lookup is now constant time Promises QoS, for instance low jitter Higher level protocols use the ATM Adaptation Layer (AAL)

2 MPLS (Multi Protocol Label Switching) Defined in RFC 3031 Combine the best of both worlds Packet forwarding Circuit switching Route at the edges, switch at the core Multi Protocol Agnostic to underlying protocols used at layer 2 or 3 Label Switching Uses labels instead of IP addresses Routing at the speed of switching Hybrid, layer 25, shim protocol MPLS Label (RFC 3032) LER (Label Edge Router) LSR (Label Switching Router) Label Exp S TTL MPLS packet label fields Label Per router local semantics Exp(erimental) 1 Class of Service S(tack) Bottom of stack indication T(ime) T(o) L(ive) Incoming IP TTL Label Edge Router Positioned at the edge of the MPLS network Adds or removes labels for incoming and outgoing traffic Also called Edge Label Switch Router (elsr) Label Switch Router Positioned in the core of the MPLS network Swaps labels and forwards packets Does not need to know about IP forwarding 1 Renamed to TC (Traffic Class) by RFC 5462

3 FEC (Forwarding Equivalence Class) and LSP (Label Switched Path) LIB (Label Information Base) Forwarding Equivalence Class Packets which are forwarded in the same manner Each label on a link determines a unique FEC Every FEC is associated with a certain LSP Label Switched Path Sequence of intermediate routers (on same stack depth) on the path from ingress to egress router Hop-by-hop versus explicit routing Every LSP is unidirectional Mapping between previous hop (incoming port, label) and FEC Mapping between FEC and next hop (outgoing port, label) Each router has its own LIB Details are implementation dependent Generates an LFIB (Label Forwarding Information Base) Input Port Incoming Port Label Output Port Outgoing Port Label 1 green 3 blue 2 red 1 orange MPLS Operation (continued) MPLS Separation of Control and Data Receive IP packet at edge router 1 Classify into FEC green 2 Push (label green) 3 Swap (label green, label red) 4 Swap (label red, label blue) 5 Pop (label blue) 6 Forward IP packet to destination Control Plane Exchange layer 3 and label information Several label distribution protocols (LDP, CR-LDP, RSVP-TE) Also piggybacked on routing protocols (OSPF-TE, ISIS-TE, MP-BGP) Data Plane Switch (forward) packets based on labels Push (ingress) Swap (intermediate) Swap and push (start LSP tunnel) Pop and swap (end LSP tunnel) Pop (egress)

4 LDP (Label Distribution Protocol) RSVP-TE (Resource Reservation Protocol Traffic Engineering) UDP discovery and TCP session with peers Adjacent LSRs inform each other of the label bindings Downstream LSR determines the label On demand or unsolicited An IGP protocol is configured on all LSRs New IGP routes lead to new label bindings Labels can be withdrawn when IGP routes are no longer valid Hard-state Expected to work until explicitly torn down Extension of RSVP Unreliable delivery (protocol 46; sometimes UDP) Soft-state Information needs to be periodically refreshed An LSP is created by propagating an RSVP message to the endpoint Paths are terminated if not refreshed on time Applications (1) Applications (2) TE (Traffic Engineering) Traffic steering across network in order to fully utilize resources With the help of RSVP-TE and OSPF-TE or IS-IS-TE Full network view (OSPF, IS-IS) and extra information about link state RSPV-TE creates LSPs on demand QoS (Quality of Service) Different types of service across the network Enforcing drop probability, bandwidth and delay (queueing) CoS bits or FEC (destination + class of service) VPN (Virtual Private Network) Private connections over shared networks Layer 2 or layer 3 based Business can choose the needed type of service Stacked labels: egress router and VPN identity LDP (layer 2) or BGP (layer 3) is used to transport label information

5 Layer 2 VPN (1) Layer 2 VPN (2) AToM (Any Transport over MPLS) Transports layer 2 frames over an ATM, Frame-Relay, PPP, Ethernet Point-to-point service From ingress router/interface to egress router/interface Identified by using an inner label VPLS (Virtual Private LAN Service) Transports layer 2 frames over an Works multipoint-to-multipoint The IP/MPLS core operates as a big virtual switch Outer label used for normal MPLS forwarding Inner label used for VPLS instances Layer 3 VPN Uses the MP-BGP (Multi Protocol BGP) extension of BGP Introduces the VPN-IPv4 address family Extends the 32-bit IPv4 address with a 64-bit RD (route distinguisher) A BGP route for VPN-IPv4 includes an MPLS label Each VPN has its own VRF (VPN Routing and Forwarding) instance Keeping separate routing tables for the VPNs Also separate from the global routing table MPLS forwarding uses stacked labels Outer label for LSP forwarding Inner label to differentiate between different VPNs