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IP/MPLS

IP/MPLS. BXR-48000 Switch Router. Objectives. Explain the need for MPLS List the components of MPLS Describe the responsibilities of a Label Switch Router (LSR) Explain the details associated with Label exchange Discuss the concept of Ships in the Night (SIN). Expanding IP Networks.

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IP/MPLS

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  1. IP/MPLS BXR-48000 Switch Router

  2. Objectives • Explain the need for MPLS • List the components of MPLS • Describe the responsibilities of a Label Switch Router (LSR) • Explain the details associated with Label exchange • Discuss the concept of Ships in the Night (SIN)

  3. Expanding IP Networks IP Network Source Destination • Traditionally, IP is connectionless • Forwarding is a hop-by-hop IP header look-up operation • Best effort service -- connectionless approach does not guarantee Quality of Service • More predictable methods exist

  4. History of the Overlay Network • ATM networks offered performance and predictable behavior, via connection-orientation (late 1990s) • Service providers created “overlay” networks that presented a virtual topology to the edge routers in their network • Physical links become invisible to routers • Virtual circuits carry traffic to router destinations • With ATM supporting IP, the virtual network could be reengineered without changing the physical network • Virtual connections can be added or deleted at will • Bandwidth assignment is done per VC

  5. + Traffic Engineering in Overlay Networks Traffic Engineering is steering the traffic to the available bandwidth X Y X Z Z Y Logical View

  6. + Scaling Problem in Point-to-Point Networks • Each router needed IP adjacency with every other (N2) • As the router count increased, significant resources were consumed NewCustomer NewCustomer Customer Customer Customer

  7. Effects of Traffic Engineering and Overlay Networks • Advantages: • End-to-end traffic control • Use QoS benefits of ATM circuits for IP traffic • Balance the flow of traffic across links • VCs provide administrative control • Disadvantages: • Scalability limits: N2 issue with full-mesh of PVC • Large PVC count stresses routing protocols severely • Addition of new sites (PVC) makes O-A-M a complex process

  8. The MPLS Remedy • MPLS provides connection-oriented benefits to IP networks • IP traffic sent via connection-oriented Label Switched Paths (LSPs) • Multiple services run on a packet core • Traffic engineering capability for IP • Progress for QoS awareness in IP networks • DiffServe-TE mechanisms are developing • MPLS enables new applications (BGP VPNs, VPLS)

  9. MPLS Basics • MPLS makes use of labels in its headers for fast packet forwarding • Labels have local significance and the label value changes at each hop • Similar to ATM’s VPI/VCI or Frame Relay’s DLCI • Label Switched Paths (LSPs) provide the route for the MPLS traffic to reach the destination • LSPs can be built using Constrained Shortest Path First (CSPF) algorithm that takes into account traffic engineering requirements (such as bandwidth, link affinity, etc.)

  10. MPLS Components • MPLS header stack, which contains: • MPLS label used to forward the packet • Protocol components • Enhanced IP routing protocols which distribute topology and constraint-based information for traffic engineering • Label Distribution Protocols (LDPs) • Standardized connection establishment protocols • Label Switch Routers (LSRs) set up a complete path from ingress LSR to egress LSR Egress LSR (LER) Ingress LSR (LER) Transit LSR Transit LSR

  11. MPLS Header • Label is 20 bits • Label is inserted between L2 and L3 headers • Multiple labels can be stacked MPLS header IP packet Label Exp. S TTL 4 Octets

  12. MAC Header Label Layer3 Header Data Label Encoding for Multi-Service • MPLS runs over multiple layer 2 protocols • Labels are placed as shown ShimATM Label ATM Header Label Layer3 Header Data LC-ATM VPI VCI PTI CLP HEC Data VPI VCI Label PPP Header Label Layer3 Header Data Label PPP Label Ethernet

  13. MPLS Protocol Components • Extensions to Routing Protocols • OSPF-TE • IS-IS-TE • Multi-Protocol BGP (for BGP-based MPLS-VPN) • IP/MPLS Signaling Protocols • RSVP-TE for best effort or traffic engineered flows • LDP for best effort flows

  14. + 150 Data IP Header PPP Hdr. Label Swap IN OUT Port Label Port Label 5 150 7 216 216 216 Payload Payload MPLS Terminology • MPLS – Multi-Protocol Label Switching • Label-switching technology that utilizes Layer 3 for route calculation, and Layer 2 to provide simple fast packet forwarding • Layer 3 is IP, Layer 2 can be ATM, Frame Relay, PPP, Ethernet MPLS with Packet over SONET LSR MPLS with ATM

  15. LSR LSR LSR MPLS Terminology (cont) • LSR – Label Switch Router • Device participating in the MPLS domain • Swaps labels as packets traverse MPLS nodes along a defined path • LSP – Label Switched Path • A route through the MPLS domain where an incoming label is linked to an outgoing label through LSRs • Can be static or dynamic LSR

  16. Label Switch Router (LSR) Responsibilities • Runs IP routing protocols • Aware of IP topology • Runs Label Distribution Protocols • Establishes LSPs • Forwards packets via MPLS • Label switching on labeled packets • Assigns labels to IP traffic headed for an LSP • Removes labels from IP traffic destined for local IP interfaces • Performs normal IP forwarding • In cases where MPLS does not reach the destination

  17. Types of LSRs • LER – Label Edge Router (a.k.a Ingress or Egress LSR) • Router/Switch at the ingress or egress of the MPLS domain • Adds labels on ingress and removes labels on egress • Transit LSR • Participates in routing protocols • Forwards traffic on pre-established LSPs Ingress LSR (LER) Egress LSR (LER) TransitLSR TransitLSR MPLS Domain

  18. Packet Label Ingress LSR / Label Edge Router (LER) • First LSR in the LSP • Examines destination address of inbound IP packets • Classifies packet to a Forwarding Equivalence Class (FEC) • Generates MPLS header and assigns initial label (PUSH) • Forwarded to the next-hop in the LSP Ingress LSR (LER) Egress LSR (LER) TransitLSRs MPLSInterface IPInterface MPLS Domain Packet Traffic flow

  19. TransitLSRs Ingress LSR (LER) Egress LSR (LER) MPLSInterface MPLSInterface MPLS Domain Packet Label Packet Label Traffic flow Transit LSR • Perform exact match on incoming label • Lookup outgoing interface and label • Swap the labels and forward the packet • Much less processing than typical L3 lookup/forward

  20. Packet Label Egress LSR / Label Edge Router (LER) • Last LSR in the LSP • LSR removes the label (POP) • Perform Layer 3 IP lookup • Forwards the IP packet to outside of MPLS network IPInterface MPLSInterface Egress LSR (LER) Ingress LSR (LER) TransitLSRs MPLS Domain Packet Traffic flow

  21. Label Switched Path Characteristics • End-to-end path followed through the MPLS domain • LSPs are in general unidirectional • LSPs are setup using explicit routing from Ingress LSR or hop-by-hop using IGP database • Manual configuration • Automatic path computation

  22. Types of LSPs • Static LSPs or P-LSPs where user specifies incoming and outgoing label at every hop • Similar to ATM and Frame Relay PVCs • Dynamic LSPs built by the ingress LSR towards a specified destination • Can use IGP-similar to IP hop-by-hop routing • Can introduce traffic engineering to build TE-LSPs • TE-LSPs can be built accounting for priority, bandwidth, link affinity -similar to ATM’s SPVCs • Hose and Pipe LSPs - Point-to-Cloud, Point-to-Point models • Hose - point-to-cloud model and committed access rate • Pipe - point-to-point model and committed information rate • BXR has support for all the above LSPs

  23. IP Packet Label Explicit NULL • Q: How does the LSR know it is the egress? A: Using the label value (null) • Label 0 ( 2 in IPv6) • Indicates the label has to be popped and the packet’s IP header used for forwarding • Egress LSR performs two lookups • Not a common method Ingress LSR R4 R3 R2 R1 IP Packet IP Packet Label=0 IP Packet Label IP Packet

  24. Egress LSR Ingress LSR R4 R3 R2 R1 IP Packet IP Packet Label IP Packet IP Packet Label Implicit NULL • When Implicit null label is used, penultimate hop does the label popping – called Penultimate Hop Popping (PHP) • Useful where the Egress LSR does not have the ‘horsepower’ to do two lookups and still provide line rate performance • Allows the egress LSR to request a label POP operation from its upstream neighbor • Egress LSR has to do only one lookup (IP address) • Used by BXR-48000 but we can handle explicit null

  25. Label Modes • Label Distribution Mode - The way a label-FEC mapping is distributed between peers • Downstream on Demand (DoD) • Downstream Unsolicited (DU) • Label Distribution Control Mode - the decision as to when to send the label-FEC mapping upstream • Independent label distribution control • Ordered label distribution control

  26. Label Mode - Distribution Downstream Unsolicited Downstream on Demand LSR2 LSR1 LSR2 LSR1 Label-FEC Binding Request for Binding • LSR2 discovers a ‘next hop’ for a particular FEC • LSR2 generates a label for the FEC and communicates the binding to LSR1 • LSR1 inserts the binding into its forwarding tables • If LSR2 is the next hop for the FEC, LSR1 can use that label knowing that its meaning is understood Label-FEC Binding • LSR1 recognizes LSR2 as its next-hop for an FEC • A request is made to LSR2 for a binding the FEC and a label • If LSR2 recognizes the FEC and has a next hop for it, it creates a binding and replies to LSR1 Both methods are supported; Peer negotiation must first agree on distribution method

  27. Label Mode - Distribution Control • MPLS path forms as associations are made between FEC next-hops and incoming and outgoing labels Ordered LSP Control Independent LSP Control • Label-FEC binding is communicated to peers if: • - LSR is the ‘egress’ LSR to particular FEC Or • - label binding has been received from upstream LSR • LSP formation ‘flows’ from egress to ingress • 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 Definition • Labels can be exchanged with less delay • 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 • Mechanism for consistent granularity and freedom from loops • Used for explicit routing • BXR-4800 uses it Comparison

  28. + Request: 47.1 Request: 47.1 Mapping: 0.50 Mapping: 0.40 LSP Build-Up – Simplified 47.1 1 3 2 1 3 2 1 3 47.3 47.2 2

  29. RSVP-TE LSP Build-Up R9 R8 R3 R4 R2 Pop R5 R1 Label 32 Label 49 R6 R7 Label 17 Label 22 Setup: Path (ERO = R1->R2->R6->R7->R4->R9) Reply: Resv communicates labels and reserves bandwidth on each link

  30. LSP Setup - Detailed Example Outgoing I/F: 192.168.1.151 Outgoing MPLS label: 1000 NHOP I/F: 192.168.1.151 NHOP Address: 92.168.1.152 Ingress I/F: 192.168.3.154 Incoming MPLS label: ipv4-implicit-null NHOP Address:127.0.0.1 1.152 192.168.25.151 3.154 2.152 3.153 50.154 1.151 2.153 Ingress I/F: 192.168.1.152 Incoming MPLS label: 1000 Egress I/F: 192.168.2.152 Outgoing MPLS label: 2000 NHOP I/F: 192.168.2.152 NHOP Address: 192.168.2.153 Ingress I/F: 192.168.2.153 Incoming MPLS label: 2000 Egress I/F: 192.168.3.153 Outgoing MPLS label: ipv4-implicit-null NHOP I/F: 192.168.3.153 NHOP Address: 192.168.3.154

  31. Ships in the Night (SIN) • Running both MPLS and ATM control planes integrated on the same interface/ link is defined by IETF as “Ships in the Night”- IETF SIN; the device is an integrated switch router • ATM and IP/MPLS domains and services converge • Running both MPLS and ATM control planes on the same node but on different interfaces/links is called Hybrid SIN* • ATM and IP/MPLS domains and services remain distinct and separate • Retain and grow premium ATM services as independent offering and add new IP/MPLS services • BXR supports both (* Hybrid SIN is a Marconi term and is used to differentiate from IETF SIN)

  32. Network Evolution Options ATM and MPLS control plane over cells (on the same port) Ships in the Night (SIN) ATM MPLS ATM ATM and MPLS interworking via PWE3 Broadband Gateway ATM MPLS MPLS Router ATM Switch Hybrid Network Separate ATM and MPLS networks on a single platform ATM MPLS The BXR-48000 provides three evolutionary approaches to arrive at a packet-based infrastructure

  33. Summary • Explained the need for MPLS • Listed the components of MPLS • Described the responsibilities of a Label Switch Router (LSR) • Explained the details associated with Label exchange • Discussed the concept of Ships in the Night (SIN)

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