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MPLS Tutorial Bilel N. Jamoussi, Ph.D. Senior Network Architect Carrier Data Networks [email protected] Tutorial Outline • Overview • Label Encapsulations • Label Distribution Protocols • MPLS and ATM • IETF Status • Nortel Networks Activity • Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 2 MPLS Motivations • Flexibility (L2/L3 Integration) — Media Support: ATM, FR, Ethernet, PPP — Operate IP over Multiservice ATM — More than destination-based Forwarding • IP Traffic Engineering — Constraint-based Routing • IP-VPN — Tunneling mechanism • VOIP — Connection-oriented Paths and QoS INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 3 All Nodes Run Standard IP Routing Dest 47.1 47.2 47.3 Dest 47.1 47.2 47.3 Out 1 2 3 Out 1 2 3 1 47.1 3 1 Dest 47.1 47.2 47.3 Out 1 2 3 2 3 2 1 47.2 47.3 3 2 INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 4 IP Destination Lookup at Each Hop Dest 47.1 47.2 47.3 Dest 47.1 47.2 47.3 Out 1 2 3 1 47.1 1 Dest 47.1 47.2 47.3 Out 1 2 3 IP 47.1.1.1 2 IP 47.1.1.1 3 Out 1 2 3 2 IP 47.1.1.1 1 47.2 47.3 3 2 IP 47.1.1.1 INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 5 Multiprotocol Label Switching (MPLS) Edge Label Switch Router (LSR) Label Switch Router Label Switch Router Edge Label Switch Router (LSR) IP Packet IP Packet IP Packet Label IP Packet IP Packet Layer 3 Routing Label Label Layer 2 Forwarding Layer 3 Routing MPLS involves routing at the edges, switching in the core INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 6 MPLS Terminology LDP: FEC: LSP: LSR: LER: Label Distribution Protocol Forwarding Equivalence Class Label Switched Path Label Switching Router Label Edge Router (Note that LER is a Nortel Networks term describing the edge LSR function) INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 7 Forwarding Equivalence Classes LSR FEC LSP FEC Packets are destined for different address prefixes, but can be mapped to common egress router, treated as equivalent FEC • FEC = “A subset of packets that are all treated the same way by a router” • The concept of FECs provides for a great deal of flexibility and scalability • In conventional routing, a packet is assigned to an FEC at each hop (i.e., L3 lookup); in MPLS, it is only done once at the network ingress INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 8 Label Switched Path — Concept Label Switched Path (LSP) Set Up Across Network Interior Nodes Forwarded Along LSP Based on Labels Incoming Packets Classified, Labeled Egress Node Removes Label Before Forwarding Two types of Label Switched Paths: • Hop-by-hop • Explicit Routing INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 9 MPLS Label Distribution Intf Label Dest Intf Label In In Out Out 3 0.50 47.1 1 0.40 Intf In 3 Label Dest Intf In Out 0.40 47.1 1 1 Request: 47.1 3 Intf Dest Intf Label In Out Out 3 47.1 1 0.50 3 2 1 1 47.1 Mapping: 0.40 2 47.3 3 47.2 2 INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 10 Label Switched Path (LSP) Intf Label Dest Intf Label In In Out Out 3 0.50 47.1 1 0.40 Intf Dest Intf Label In Out Out 3 47.1 1 0.50 Intf In 3 IP 47.1.1.1 1 47.1 3 3 1 1 Label Dest Intf In Out 0.40 47.1 1 2 2 47.3 3 47.2 2 IP 47.1.1.1 INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 11 LSPs: Explicit Routing Explicit Routing LSR A Forward to LSR B LSR C LSR D LSR E LSR D LSR B LSR E LSR C • Ingress node (or egress node) determines path from ingress to egress • Operator has routing flexibility (policy-based, QoS-based) • Required for MPLS traffic engineering • Two signaling options proposed in the standards: RSVP, CR-LDP INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 12 Traffic Engineered Path Intf Label Dest Intf Label In In Out Out 3 0.50 47.1 1 0.40 Intf In 3 3 Dest 47.1.1 47.1 Intf Out 2 1 Label Out 1.33 0.50 Intf In 3 IP 47.1.1.1 1 47.1 3 3 1 1 Label Dest Intf In Out 0.40 47.1 1 2 2 47.3 3 47.2 2 IP 47.1.1.1 INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 13 Tutorial Outline • Overview • Label Encapsulations • Label Distribution Protocols • MPLS & ATM • IETF Status • Nortel Networks Activity • Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 14 Label Encapsulation MPLS L2 Label ATM FR VPI VCI DLCI Ethernet PPP “Shim” MPLS Encapsulation is specified over various media types INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 15 MPLS Link Layers • MPLS is intended to run over multiple link layers • Specifications for the following link layers currently exist: • ATM: label contained in VCI/VPI field of ATM header • Frame Relay: label contained in DLCI field in FR header • PPP/LAN: uses ‘shim’ header inserted between L2 and L3 headers • Fields and functionality may vary between different link layers — ATM/FR have to adapt to existing structure — PPP/LAN header has more freedom to incorporate useful features (CoS, TTL) • Translation between link-layers types must be supported MPLS intended to be “multiprotocol” below as well as above INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 16 MPLS Encapsulation — ATM ATM LSR constrained by the cell format imposed by existing ATM standards 5 Octets ATM Header Format Option 1 VPI Label PT CLP HEC Label Combined Label Option 2 Option 3 VCI ATM VPI (Tunnel) Label AAL 5 PDU Frame (nx48 bytes) n ATM SAR ••• 1 Network Layer Header and Packet (e.g., IP) Generic Label Encap. (PPP/LAN format) AAL5 Trailer 48 Bytes ATM Header ATM Payload 48 Bytes ••• • Top one or two labels are contained in the VPI/VCI fields of ATM header — one in each or single label in combined field, negotiated by LDP • Further fields in stack are encoded with ‘shim’ header in PPP/LAN format — must be at least one, with bottom label distinguished with ‘explicit NULL’ • TTL is carried in top label in stack, as a proxy for ATM header (that lacks TTL) INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 17 MPLS Encapsulation — Frame Relay Generic Encap. (PPP/LAN Format) Q.922 Header n DLCI C/ E R A DLCI ••• FE BE D E CN CN E A Layer 3 Header and Packet 1 DLCI Size = 10, 17, 23 Bytes • Current label value carried in DLCI field of Frame Relay header • Can use either 2 or 4 octet Q.922 address (10, 17, 23 bytes) • Generic encapsulation contains n labels for stack of depth n — top label contains TTL (which FR header lacks), ‘explicit NULL’ label value INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 18 MPLS Encapsulation — PPP & LAN Data Links MPLS ‘Shim’ Headers (1-n) n ••• 1 Network Layer Header and Packet (e.g., IP) Layer 2 Header (e.g., PPP, 802.3) 4 Octets Label Stack Entry Format Label Exp. S TTL Label: Label Value, 20 bits (0-16 reserved) Exp.: Experimental, 3 bits (was Class of Service) S: Bottom of Stack, 1 bit (1 = last entry in label stack) TTL: Time to Live, 8 bits • Network layer must be inferable from value of bottom label of the stack • TTL must be set to the value of the IP TTL field when packet is first labeled • When last label is popped off stack, MPLS TTL to be copied to IP TTL field • Pushing multiple labels may cause length of frame to exceed layer-2 MTU — LSR must support “Max. IP Datagram Size for Labeling” parameter — any unlabeled datagram greater in size than this parameter is to be fragmented MPLS on PPP links and LANs uses ‘Shim’ Header Inserted Between Layer 2 and Layer 3 Headers INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 19 Tutorial Outline • Overview • Label Encapsulations • Label Distribution Protocols • MPLS & ATM • IETF Status • Nortel Networks Activity • Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 20 Label Distribution Protocols • Overview of Hop-by-hop and Explicit • Label Distribution Protocol (LDP) • Constraint-based Routing LDP (CR-LDP) • Extensions to RSVP • Extensions to BGP INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 21 LSPs: Hop-by-Hop vs. Explicit Routing Hop-by-Hop Routing LSR A Forward to LSR B MPLS will form label switched paths by one of two methods — hop-by-hop routing or explicit routing LSR B LSR D LSR C Forward to LSR C Forward to LSR D LSR E Forward to LSR E Forward to LSR ... • Each node runs layer 3 routing protocol • Routing decisions made independently at each node Explicit Routing LSR A LSR D LSR B LSR E LSR C Forward to LSR B LSR C LSR D LSR E • Also known as ‘source routing’ or ‘traffic steering’ • Ingress node (or egress node) determines path from ingress to egress INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 22 Comparison — Hop-by-Hop vs. Explicit Routing Hop-by-Hop Routing Explicit Routing • Distributes topology awareness • Centralized topology awareness (in ingress node) • No path setup/tear-down/refresh required • Path setup/tear-down/refresh required • Automates routing using industry standard protocols (e.g., OSPF, ISIS) • Requires manual provisioning or creation of new routing protocol • Loop detection/prevention required • Reroute on failure impacted by convergence time of routing protocol • Existing routing protocols are destination prefix-based • Backup paths may be preprovisioned for rapid restoration • Operator has routing flexibility (policy-based, QoS-based) • Easily used for traffic engineering • Difficult to perform traffic engineering, QoS-based routing Explicit routing shows great promise for traffic engineering, at the cost of operator involvement (or new routing protocols) INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 23 Explicit Routing — MPLS vs. Traditional Routing LSR A LSR D LSR B LSR E LSR C Forward to LSR B LSR C LSR D LSR E • Connectionless nature of IP implies that routing is based on information in each packet header • Source routing is possible, but path must be contained in each IP header — lengthy paths increase size of IP header, make it variable size, increase overhead — some gigabit routers require ‘slow path’ option-based routing of IP packets • Source routing has not been widely adopted in IP and is seen as impractical — some network operators may filter source-routed packets for security reasons • MPLS enables the use of source routing by its connection-oriented capabilities — paths can be explicitly set up through the network — the ‘label’ now can represent the explicitly routed path • Loose and strict source routing can be supported MPLS makes the use of source routing in the Internet practical INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 24 Label Distribution Protocol (LDP) — Purpose Label distribution ensures that adjacent routers have a common view of FEC <-> label bindings Routing Table: Routing Table: Addr-prefix 47.0.0.0/8 Addr-prefix 47.0.0.0/8 Next Hop LSR2 Next Hop LSR3 LSR1 IP Packet LSR3 LSR2 47.80.55.3 Label Information Base: Label-In FEC Label-Out XX 47.0.0.0/8 17 Step 3: LSR inserts label value into forwarding base For 47.0.0.0/8 use label ‘17’ Label Information Base: Label-In FEC Label-Out 17 47.0.0.0/8 XX Step 2: LSR communicates binding to adjacent LSR Step 1: LSR creates binding between FEC and label value Common understanding of which FEC the label is referring to! Label distribution can either piggyback on top of an existing routing protocol, or a dedicated label distribution protocol (LDP) can be created INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 25 Label Distribution — Methods Label Distribution can take place using one of two possible methods Downstream Label Distribution Downstream-on-Demand Label Distribution LSR2 LSR1 Label-FEC Binding • LSR2 and LSR1 are said to have an “LDP adjacency” (LSR2 being the downstream LSR) LSR1 LSR2 Request for Binding Label-FEC Binding • LSR2 discovers a ‘next hop’ for a particular FEC • LSR1 recognizes LSR2 as its next-hop for an FEC • LSR2 generates a label for the FEC and communicates the binding to LSR1 • A request is made to LSR2 for a binding between the FEC and a label • LSR1 inserts the binding into its forwarding tables • If LSR2 recognizes the FEC and has a next hop for it, it creates a binding and replies to LSR1 • If LSR2 is the next hop for the FEC, LSR1 can use that label knowing that its meaning is understood • Both LSRs then have a common understanding Both methods are supported, even in the same network at the same time. For any single adjacency, LDP negotiation must agree on a common method. INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 26 Distribution Control: Ordered vs. Independent MPLS path forms as associations are made between FEC next-hops and incoming and outgoing labels Next Hop (for FEC) Incoming Label Independent LSP Control Definition Example Comparison Outgoing Label Ordered LSP Control • Each LSR makes independent decision on when to generate labels and communicate them to upstream peers • Communicate label-FEC binding to peers once next-hop has been recognized • LSP is formed as incoming and outgoing labels are spliced together • Label-FEC binding is communicated to peers if: - LSR is the ‘egress’ LSR to particular FEC - Label binding has been received from upstream LSR • Cisco’s Tag Switching • IBM’s ARIS • Labels can be exchanged with less delay • Does not depend on availability of egress node • Granularity may not be consistent across the nodes at the start • May require separate loop detection/mitigation method • Requires more delay before packets can be forwarded along the LSP • Depends on availability of egress node • Mechanism for consistent granularity and freedom from loops • Used for explicit routing and multicast • LSP formation ‘flows’ from egress to ingress Both methods are supported in the standard and can be fully interoperable INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 27 Label Retention Methods Binding for LSR5 An LSR may receive label bindings from multiple LSRs LSR2 LSR1 LSR5 Binding for LSR5 Some bindings may come from LSRs that are not the valid next-hop for that FEC Binding for LSR5 LSR4 Conservative Label Retention Liberal Label Retention Label Bindings for LSR5 LSR3 LSR2 Label Bindings for LSR5 LSR1 LSR3 LSR4’s Label LSR3’s Label LSR2’s Label Valid Next Hop LSR4 • LSR maintains bindings received from LSRs other than the valid next-hop • If the next-hop changes, it may begin using these bindings immediately • May allow more rapid adaptation to routing changes • Requires an LSR to maintain many more labels LSR2 LSR1 LSR3 LSR4’s Label LSR3’s Label LSR2’s Label Valid Next Hop LSR4 • LSR only maintains bindings received from valid next-hop • If the next-hop changes, binding must be requested from new next-hop • Restricts adaptation to changes in routing • Fewer labels must be maintained by LSR Label-Retention method trades-off between label capacity and speed of adaptation to routing changes INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 28 LSPs: Hop-by-Hop Hop-by-Hop Routing LSR D LSR B LSR A Forward to LSR B Forward to LSR C LSR E LSR C Forward to LSR D Forward to LSR E Forward to LSR ... • Each node runs layer 3 routing protocol • Routing decisions made independently at each node • Distributes topology awareness • Automates routing using industry standard protocols (e.g., OSPF, ISIS) • Difficult to perform traffic engineering INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 29 Outline • CR-LDP Solution overview • CR-LDP update • CR-LDP QoS • Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 30 ER-LSP Setup using CR-LDP 1. Label Request message. It contains ER path < B,C,D>. 2. Request message processed and next node determined. Path list modified to <C,D>. 6. When LER A receives label mapping, the ER established. LER A Ingress 5. LSR C receives label to use for sending data to LER D. Label table updated. LSR B 3. Request message terminates. 4. Label mapping message originates. LSR C ER Label Switched Path LER D Egress • Simple — part of the MPLS LDP protocol • Robust — signaling built upon reliable TCP layer • Scalable — no need to refresh LSP state • Interoperable — proven multivendor interoperability INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 31 MPLS Traffic Engineering • Traffic Engineering requires a solution to route LSPs according to various constraints • Solution has to be: — Scalable — Reliable • CRLDP use LDP messages to signal these various constraints INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 32 Constraint-based LSP Setup using LDP • Uses LDP Messages & TLVs — LDP runs on a reliable transport (TCP) • Does NOT require hop-by-hop — DOD-O can be used for loose segments • Introduces additional TLVs to the base LDP specification to signal ER, and other “constraints” • TLVs for error handling & diagnostics INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 33 Why CR-LDP? • Runs on TCP Reliable • Hard State Scalable • QoS Support ATM-like, FR-like, & Diffserv — More apt to integrate/migrate in existing FR and ATM networks and to support emerging diffserev-based POS gigabit routers • Demonstrated interoperability • Simple protocol based on LDP, output of MPLS WG INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 34 Latest CRLDP Revision • Constraint-based routing overview section • CR-TLV is broken in separate TLVs — Explicit route, route pinning, pre-emption • ER-Hop TLV encoding consistent with LDP — 2-byte type, 2-byte length, variable length content • Traffic TLVs and QoS INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 35 CR-LDP TLVs • CR-LSP FEC Element — An opaque FEC element type 0x04 value (0 octet) • LSPID TLV — A CRLSP unique identifier within an MPLS network. • ER-Hop Type (4) LSPID TLV — The LSPID is used to identify the tunnel ingress point as the next hop in the ER. • Resource Class (Color) TLV — 32 bit mask indicating which of the 32 "administrative groups" or "colors" of links the CRLSP can traverse. INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 36 CR-LDP Label Request Message U F Label Request Message Length Message ID TLV Return Message ID TLV FEC TLV LSPID TLV ER-TLV Traffic Parameters TLV Optional Pinning TLV "Resource Class" TLV Pre-emption TLV INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 37 CRLDP Traffic and QoS • In the crldp-00 draft three service classes (delay sensitive, throughput sensitive and best effort) were defined. • This is inflexible and it's hard to map existing and new applications onto these service definitions. • In crldp-01 only CRLSP traffic and QoS parameters of a CRLSP are defined. These describe the characteristics of the CRLSP. Loosely routed segment Unlabeled IP CRLDP MPLS domain HBH only MPLS domain INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 38 Traffic Parameters TLV Flags control “negotiability” of parameters U F Traf. Param. TLV Flags Frequency Length Reserved Weight Peak Data Rate (PDR) Peak Burst Size (PBS) Committed Data Rate (CDR) Committed Burst Size (CBS) Excess Burst Size (EBS) 32 bit fields are short IEEE floating point numbers Any parameter may be used or not used by selecting appropriate values Frequency constrains the variable delay that may be introduced Weight of the CRLSP in the “relative share” Peak rate (PDR+PBS) maximum rate at which traffic should be sent to the CRLSP Committed rate (CDR+CBS) the rate that the MPLS domain commits to be available to the CRLSP Excess Burst Size (EBS) to measure the extent by which the traffic sent on a CRLSP exceeds the committed rate INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 39 CRLSP characteristics not edge functions • The approach is like diffserv’s separation of PHB from edge • The parameters describe the “path behavior” of the CRLSP, i.e., the CRLSP’s characteristics • Dropping behavior is not signaled — Dropping may be controlled by DS packet markings • CRLSP characteristics may be combined with edge functions (which are undefined in CRLDP) to create services — Edge functions can perform packet marking — Example services are in an appendix INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 40 Peak Rate • The maximum rate at which traffic should be sent to the CRLSP • Defined by a token bucket with parameters — Peak data rate (PDR) — Peak burst size (PBS) • Useful for resource allocation • If a network uses the peak rate for resource allocation then its edge function should regulate the peak rate • May be unused by setting PDR or PBS or both to positive infinity INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 41 Committed Rate • The rate that the MPLS domain commits to be available to the CRLSP • Defined by a token bucket with parameters — Committed data rate (CDR) — Committed burst size (CBS) • Committed rate is the bandwidth that should be reserved for the CRLSP • CDR = 0 makes sense; CDR = + less so • CBS describes the burstiness with which traffic may be sent to the CRLSP INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 42 Excess Burst Size • Measure the extent by which the traffic sent on a CRLSP exceeds the committed rate • Defined as an additional limit on the committed rate’s token bucket • Can be useful for resource reservation • If a network uses the excess burst size for resource allocation then its edge function should regulate the parameter and perhaps mark or drop packets • EBS = 0 and EBS = + both make sense INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 43 Frequency • Specifies how frequently the committed rate should be given to CRLSP • Defined in terms of “granularity” of allocation of rate • Constrains the variable delay that the network may introduce • Constrains the amount of buffering that an LSR may use • Values: — Very frequently: no more than one packet may be buffered — Frequently: only a few packets may be buffered — Unspecified: any amount of buffering is acceptable INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 44 Weight • Specifies the CRLSP’s weight in the “relative share algorithm” • Implied but not stated: — CRLSPs with a larger weight get a bigger relative share of the “excess bandwidth” • Values: — 0 — the weight is not specified — 1-255 — weights; larger numbers are larger weights • The definition of “relative share” is network specific INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 45 Negotiation Flags PDR Negotiation Flag PBS Negotiation Flag CDR Negotiation Flag CBS Negotiation Flag EBS Negotiation Flag Weight Negotiation Flag Res F6 F5 F4 F3 F2 F1 If a parameter is flagged as negotiable then LSRs may replace the parameter value with a smaller value in the label request message. LSRs descover the negotiated values in the label mapping message. Label request - possible downward negotiation Label mapping no negotiation INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 46 ER-LSP Setup Using RSVP 2. New path state. Path message sent to next node. 1. Path message. It contains ER path < B,C,D>. 5. When LER A receives Resv, the ER established. LER A 3. Resv message originates. Contain the label to use and the required traffic/QoS para. 4. New reservation state. Resv message propagated upstream. 6. ResvConf message (o). LSR B LSR C Per-hop Path and Resv refresh unless suppressed. LER D • More complex — signaling in addition to MPLS LDP protocol • Unreliable — signaling built upon UDP • Scalability concerns — Significant number of refresh messages to process • Interoperability concerns — IETF draft underspecified, no proven interoperability INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 47 BGP Extensions • A mechanism to exchange label binding information among BGP peers by adding (piggybacking) the label mapping information on the BGP route update INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 48 Tutorial Outline • Overview • Label Encapsulations • Label Distribution Protocols • MPLS & ATM • IETF Status • Nortel Networks Activity • Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 49 MPLS & ATM • Various Modes of Operation — Label-controlled ATM — Tunneling through ATM — Ships in the night with ATM • ATM Merge — VC merge — VP merge INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 50 MPLS & ATM Several models for running MPLS on ATM: 1. Label-Controlled ATM: • Use ATM hardware for label switching • Replace ATM Forum SW by IP/MPLS IP Routing MPLS ATM HW INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 51 Label-Controlled ATM • Label switching is used to forward network-layer packets • It combines the fast, simple forwarding technique of ATM with network layer routing and control of the TCP/IP protocol suite Label Switching Router Network Layer Routing (e.g., OSPF, BGP4) Switched path topology formed using network layer routing (i.e., TCP/IP technique) Forwarding Table Forwarding Table B 17 C 05 • • • Label Port A C IP Packet 05 Label IP Packet 17 B D Packets forwarded by swapping short, fixed-length labels (i.e., ATM technique) ATM Label Switching is the combination of L3 routing and L2 ATM switching INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 52 2. MPLS Over ATM MPLS MPLS L S R ATM Network L S R Two Models VP VC Internet Draft: VCID notification over ATM Link INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 53 3. Ships in the Night L S R L S R MPLS ATM ATM SW ATM SW • ATM Forum and MPLS control planes both run on the same hardware but are isolated from each other, i.e., they do not interact. • This allows a single device to simultaneously operate as both an MPLS LSR and an ATM switch. • Important for migrating MPLS into an ATM network. INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 54 Ships in the Night Requirements • Resource Management — VPI.VCI Space Partitioning — Traffic management – Bandwidth Reservation – Admission Control – Queuing & Scheduling – Shaping/Policing — Processing Capacity INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 55 Bandwidth Management Port Capacity A. Full Sharing MPLS Pool 1 • MPLS • ATM ATM Available B. Protocol Partition Pool 1 • 50% • ATM MPLS Available Pool 2 ATM • 50% • rt-VBR Available C. Service Partition MPLS Pool 1 • 50% • rt-VBR ATM • COS2 Available Pool 2 MPLS • 50% • nrt-VBR ATM • COS1 Available • Bandwidth Guarantees • Flexibility INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 56 ATM Merge • Multipoint-to-point capability • Motivation — Stream Merge to achieve scalability in MPLS: – O(n) VCs with Merge as opposed to O(n2) for full mesh – Less labels required — Reduce number of receive VCs on terminals • Alternatives — Frame-based VC Merge — Cell-based VP Merge INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 57 Stream Merge Input cell streams 1 1 1 in out 1 7 2 3 2 2 2 3 3 6 9 6 7 9 6 7 9 6 7 Non-VC merging (Nin–Nout) Input cell streams 1 1 1 2 2 2 3 3 in 1 2 3 out 7 7 7 7 7 7 7 7 7 7 7 AAL5 Cell Interleaving Problem 7 7 7 7 7 7 7 7 No Cell Interleaving VC merging (Nin-1out) INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 58 VC-Merge: Output Module Reassembly buffers Output buffer Merge Passport is VC-Merge Capable INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 59 VP-Merge VCI=1 Option 1: Dynamic VCI Mapping VCI=2 VPI=1 No Cell Interleaving Problem Since VCI is Unique VCI=1 VCI=2 VPI=2 VCI=3 VPI=3 Option 2: Root Assigned VCI VCI=3 –merge multiple VPs into one VP –use separate VCIs within VPs to distinguish frames –less efficient use of VPI/VCI space, needs support of SVP INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 60 Tutorial Outline • Overview • Label Encapsulations • Label Distribution Protocols • MPLS & ATM • IETF Status • Nortel Networks Activity • Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 61 Proposed Standard RFCs • MPLS Label Stack Encoding <draft-ietf-mpls-labelencaps-03.txt> • Use of Label Switching on Frame Relay Networks Specification <draft-ietf-mpls-fr-03.txt> • MPLS using ATM VC Switching <draft-ietf-mpls-atm01.txt> • Multiprotocol Label Switching Architecture <draft-ietfmpls-arch-04.txt> INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 62 Last Call • Gone through Last Call: — Label Distribution Protocol • Going to last call: — Constraint-based Label Distribution Protocol — Extensions to RSVP for LSP Tunnels — RSVP Refresh Reduction Extensions INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 63 Tutorial Outline • Overview • Label Encapsulations • Label Distribution Protocols • MPLS & ATM • IETF Status • Nortel Networks Activity • Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 64 Nortel’s Activity • IETF • Interoperability Demonstration — CR-LDP • Implementation — Traffic Engineering — VPN INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 65 Progress: Consensus Plus Running Code • 14 vendors & ISPs collaborated on CRLDP • MPLS WG document in Orlando • CRLDP is included by reference in the LDP Specification • LDP Spec has gone through last call • Demonstrated interoperability among three Vendors’ implementations in November ’98 • CRLDP is simple, stable, robust, and easily extendible • CR-LDP WG document is going to last call INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 66 Leading Key MPLS Standards • Label Distribution Protocol (LDP) — Loa Andersson & Andre Fredette • Constraint-based Routing LDP (CR-LDP) — Bilel Jamoussi, Andre Fredette, Loa Andersson, Osama AbouldMagd, & Peter Ashwood-Smith • QoS Resource Management in MPLS-Based Networks — Osama Aboul-Magd & Bilel Jamoussi with Jerry Ash, AT&T • MPLS using ATM VP Switching — Bilel Jamoussi & Nancy Feldman, IBM • Explicit Tree Routing — Swee Loke INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 67 Hosting MPLS Multivendor Interoperability Demo • MPLS over ATM • Protocol implemented according to: — CRLSP over LDP Spec. — Explicit Routing (ER) — Bw Reservation — QoS signaling • VC-Merge • Ships in the Night • Has been Tested for Interoperability with Bay BN router, Ericsson & GDC INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 68 Demo Description • Demo of five node network — Three MPLS LSRs based on ATM switches: – Ericsson AXI537, GDC Apex, Nortel Networks Passport — Two Nortel Networks MPLS LERs based on BN/ARE routers • MPLS/IP links are OC3 ATM • IP/Ethernet links are 10baseT • All LERs/LSRs capable of LDP and CR-LDP functions INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 69 Demo Interoperability Network A4 A2 LSR 2 LSR 3 Nortel Networks Passport Ericsson AXD311 A3 A0 A1 PC1 PC2 E22 A5 LER 2 Nortel Networks A51 BN/ARE A4 A51 LER 1 LSR 1 A6 GDC APEX E22 A8 INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA A41 Nortel Networks BN/ARE MPLS Tutorial 70 Experience Gained • Clear intent and structure of LDP — Fast implementation — Simple implementation • LDP flexibility — Made implementing CR-LDP easy — Frame format flexibility helped INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 71 Promoting Open Standard www.nortelnetworks.com/mpls C Source code of LDP/CRLDP message and TLV processing According to the latest Specs: LDP: <draft-ietf-mpls-ldp-03> CR-LDP: <draft-ietf-mpls-cr-ldp01> Freely available to anyone Objective: promote interoperability INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 72 Passport 6400/7400/15000 MPLS • Q399 — Passport 6400/7400/15000 LSR over ATM – Strict ER – Hop-by-hop – QoS mapping – Failure handling and recovery – Interoperability with BN router — Passport 6400/7400/15000 LER – Support for terminating and initiating LSPs – FEC configuration – QoS-based mapping of traffic onto LSPs – MVR over MPLS • Q499 — MPLS over Frame Relay INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 73 Passport 6400/7400/15000 as an LSR • BN router can do the LER capability • Passport current edge switch position in the network makes it an LSR candidate • Passport can intemperate with Cisco at edge based on MPLS Standard LDP LER LSR LER FEC LDP INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 74 Passport 6400/7400/15000 as an LER • Provides ability to interface to legacy non-MPLS literate routers and take advantage of MPLS in the network • Provides support for MPLS as a transport for MVR LER LSR LER FEC LDP INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 75 MPLS interconnecting MVRs • LSPs established between CVRs • Label Stacking between VRn and CVRx • BGP or LDP sessions established to distribute reachability and Label INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 76 Tutorial Outline • Overview • Label Encapsulations • Label Distribution Protocols • MPLS & ATM • IETF Status • Nortel Networks Activity • Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 77 Summary of Motivations for MPLS • Simplified forwarding based on exact match of fixed-length label – Initial drive for MPLS was based on existance of cheap, fast ATM switches • Separation of routing and forwarding in IP networks – Facilitates evolution of routing techniques by fixing the forwarding method – New routing functionality can be deployed without changing the forwarding techniques of every router in the Internet • Facilitates the integration of ATM and IP – Allows carriers to leverage their large investment of ATM equipment – Eliminates the adjacency problem of VC-mesh over ATM • Enables the use of explicit routing/source routing in IP networks – Can be easily used for such things as traffic management, QoS routing • Promotes the partitioning of functionality within the network – Move granular processing of packets to edge; restrict core to packet forwarding – Assists in maintaining scalability of IP protocols in large networks • Improved routing scalability through stacking of labels – Removes the need for full routing tables from interior routers in transit domain; only routes to border routers are required • Applicability to both cell and packet link-layers – Can be deployed on both cell (e.g., ATM) and packet (e.g., FR, Ethernet) media – Common management and techniques simplifies engineering Many drivers exist for MPLS above and beyond high-speed forwarding INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 78 IP and ATM Integration IP over ATM VCs IP over MPLS • ATM cloud invisible to Layer 3 Routing • ATM network visible to Layer 3 Routing • Full mesh of VCs within ATM cloud • Singe adjacency possible with edge router • Many adjacencies between edge routers • Hierachical network design possible • Topology change generates many route updates • Reduces route update traffic and power needed to process them • Routing algorithm made more complex MPLS eliminates the “n-squared” problem of IP over ATM VCs INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 79 Traffic Engineering B Demand C A D Traffic engineering is the process of mapping traffic demand onto a network Network Topology Purpose of traffic engineering: • Maximize utilization of links and nodes throughout the network • Engineer links to achieve required delay, grade-of-service • Spread the network traffic across network links, minimize impact of single failure • Ensure available spare-link capacity for rerouting traffic on failure • Meet policy requirements imposed by the network operator Traffic engineering key to optimizing cost/performance INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 80 Traffic Engineering Alternatives Current methods of traffic engineering: Manipulating routing metrics Difficult to manage Use PVCs over an ATM backbone Not scalable Overprovision bandwidth Not economical MPLS provides a new method to do traffic engineering (traffic steering) Example Network: Ingress node explicitly routes traffic over uncongested path Chosen by Traffic Eng. (least congestion) Congested Node Chosen by routing protocol (least cost) Potential benefits of MPLS for traffic engineering: - Allows explicitly routed paths - No “n-squared” problem - Per FEC traffic monitoring - Backup paths may be configured operator control scalable granularity of feedback redundancy/restoration MPLS combines benefits of ATM and IP-layer traffic engineering INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 81 MPLS Traffic Engineering Methods • MPLS can use the source routing capability to steer traffic on desired path • Operator may manually configure these in each LSR along the desired path — Analogous to setting up PVCs in ATM switches • Ingress LSR may be configured with the path, RSVP used to set up LSP — Some vendors have extended RSVP for MPLS path setup • Ingress LSR may be configured with the path, LDP used to set up LSP — Many vendors believe RSVP not suited • Ingress LSR may be configured with one or more LSRs along the desired path, hop-by-hop routing may be used to set up the rest of the path — A.k.a loose source routing, less configuration required • If desired for control, route discovered by hop-by-hop routing can be frozen — A.k.a “route pinning” • In the future, constraint-based routing will offload traffic engineering tasks from the operator to the network itself INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 82 MPLS: Scalability Through Routing Hierarchy AS1 BR2 AS2 TR1 BR1 AS3 TR2 BR3 TR4 Ingress router receives packet Packet labeled based on egress router TR3 BR4 Forwarding in the interior based on IGP route Egress border router pops label and fwds. • Border routers BR1-4 run an EGP, providing inter-domain routing • Interior transit routers TR1-4 run an IGP, providing intra-domain routing • Normal layer 3 forwarding requires interior routers to carry full routing tables — Transit router must be able to identify the correct destination ASBR (BR1-4) • Carrying full routing tables in all routers limits scalability of interior routing — Slower convergence, larger routing tables, poorer fault isolation • MPLS enables ingress node to identify egress router, label packet based on interior route • Interior LSRs would only require enough information to forward packet to egress MPLS increases scalability by partitioning exterior routing from interior routing INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 83 MPLS: Partitioning Routing and Forwarding Based on: Routing OSPF, IS-IS, BGP, RIP Forwarding Table Forwarding Classful Addr. Prefix? Classless Addr. Prefix? Multicast Addr.? Port No.? ToS Field? Based on: MPLS Exact Match on Fixed-Length Label • Current network has multiple forwarding paradigms — Class-ful longest prefix match (Class A,B,C boundaries) — Classless longest prefix match (variable boundaries) — Multicast (exact match on source and destination) — Type-of-service (longest prefix. match on addr. + exact match on ToS) • As new routing methods change, new route lookup algorithms are required — Introduction of CIDR • Next generation routers will be based on hardware for route lookup — Changes will require new hardware with new algorithm • MPLS has a consistent algorithm for all types of forwarding; partitions routing/forwarding — Minimizes impact of the introduction of new forwarding methods MPLS introduces flexibility through consistent forwarding paradigm INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 84 Upper Layer Consistency Across Link Layers Ethernet PPP (SONET, DS-3 etc.) ATM Frame Relay • MPLS is “multiprotocol” below (link layer) as well as above (network layer) • Provides for consistent operations, engineering across multiple technologies • Allows operators to leverage existing infrastructure • Co-existence with other protocols is provided for — e.g., “Ships in the Night” operation with ATM, muxing over PPP MPLS positioned as end-to-end forwarding paradigm INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 85 Summary • MPLS is a promising emerging technology • Basic functionality (Encapsulation and basic Label Distribution) has been defined by the IETF • Nortel Networks is taking an active role in defining key aspects of MPLS standard and providing support of MPLS on the Bay and Nortel Networks platforms INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA MPLS Tutorial 86