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LDP

LDP. Label Distribution Protocol. 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. LDP

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LDP

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  1. LDP Label Distribution Protocol

  2. 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 • LDP • CR-LDP • RSVP-TE Hop by Hop routing Ensures routers agree on bindings between FEC’s and the labels. Label paths follow same route as conventional routed path

  3. 1. Existing routing protocols (e.g. OSPF, IS-IS, BGP) establish routes. In an ISP environment, all routers need all routes (full BGP mesh or confeds or reflectors). IP Forwarding

  4. Router Example: Distributing Routing Information AddressPrefix I/F Address Prefix Address Prefix I/F I/F 128.89 0 128.89 0 128.89 1 ... 1 1 171.69 171.69 ... ... 128.89 0 You can reach 128.89 through me 0 1 You can reach 128.89 and 171.69 through me 1 171.69 You can reach 171.69 through me Routing Updates (OSPF, EIGRP, …)

  5. 128.89 Router Example: Forwarding Packets Address Prefix I/F Address Prefix Address Prefix 128.89 0 I/F I/F 1 128.89 0 ... 1 1 171.69 171.69 ... ... 128.89 0 128.89.25.4 Data 0 128.89.25.4 Data 1 1 128.89.25.4 Data 128.89.25.4 Data 171.69 Packets Forwarded Based on IP Address

  6. 1. Existing routing protocols (e.g. OSPF, IGRP) establish routes. 2a. Label Distribution Protocol (e.g., LDP) establishes label to routes mappings MPLS: Forwarding

  7. 1. Existing routing protocols (e.g. OSPF, IGRP) establish routes. 2b. Label Distribution Protocol (e.g., LDP) creates LFIB entries on LSRs 2a. Label Distribution Protocol (e.g., LDP) establishes label to routes mappings MPLS: Forwarding

  8. 1. Existing routing protocols (e.g. OSPF, IGRP) establish routes. 2b. Label Distribution Protocol (e.g., LDP) creates LFIB entries on LSRs 2a. Label Distribution Protocol (e.g., LDP) establishes label to routes mappings 3. Ingress edge LSR receives packet, performs Layer 3 value-added services, and “label” packets MPLS: Forwarding

  9. 1. Existing routing protocols (e.g. OSPF, IGRP) establish routes. 2b. Label Distribution Protocol (e.g., LDP) creates LFIB entries on LSRs 2a. Label Distribution Protocol (e.g., LDP) establishes label to routes mappings 3. Ingress edge LSR receives packet, performs Layer 3 value-added services, and “label” packets 4. LSRs forward labelled packets using label swapping MPLS: Forwarding

  10. 1. Existing routing protocols (e.g. OSPF, IGRP) establish routes. 2b. Label Distribution Protocol (e.g., LDP) creates LFIB entries on LSRs 2a. Label Distribution Protocol (e.g., LDP) establishes label to routes mappings 5. Edge LSR at egress removes label and delivers packet 3. Ingress edge LSR receives packet, performs Layer 3 value-added services, and “label” packets 4. LSRs forward labelled packets using label swapping MPLS: Forwarding

  11. MPLS Example:Assigning Labels In Lbl Address Prefix Out I’face Out Lbl In Lbl Address Prefix Out I’face Out Lbl In Lbl Address Prefix Out I’face Out Lbl 4 9 9 - - 4 128.89 1 128.89 0 128.89 0 5 7 - 5 171.69 1 171.69 1 ... ... ... ... ... ... 128.89 0 0 1 Use label 9 for 128.89 Use label 4 for 128.89 and Use label 5 for 171.69 1 171.69 Use label 7 for 171.69 Label Distribution Protocol (LDP)

  12. MPLS Example:Forwarding Packets In Lbl Address Prefix Out I’face Out Lbl In Lbl Address Prefix Out I’face Out Lbl In Lbl Address Prefix Out I’face Out Lbl 4 9 9 - - 4 128.89 1 128.89 0 128.89 0 5 7 - 5 171.69 1 171.69 1 ... ... ... ... ... ... 128.89 0 0 1 128.89.25.4 Data 9 128.89.25.4 Data 1 128.89.25.4 Data 4 128.89.25.4 Data 171.69 Label Switch Forwards Based on Label

  13. Comparison - Hop-by-Hop vs. Explicit Routing Hop-by-Hop Routing Explicit Routing • Distributes routing of control traffic • Builds a set of trees either fragment by fragment like a random fill, or backwards, or forwards in organized manner. • Reroute on failure impacted by convergence time of routing protocol • Existing routing protocols are destination prefix based • Difficult to perform traffic engineering, QoS-based routing • Source routing of control traffic • Builds a path from source to dest • Requires manual provisioning, or automated creation mechanisms. • LSPs can be ranked so some reroute very quickly and/or backup paths may be pre-provisioned for rapid restoration • Operator has routing flexibility (policy-based, QoS-based, • Adapts well to traffic engineering Explicit routing shows great promise for traffic engineering

  14. Label Distribution Protocol (LDP) - Purpose Label distribution ensures that adjacent routers have a common view of FEC <-> label bindings Routing Table: Addr-prefix Next Hop 47.0.0.0/8 LSR3 Routing Table: Addr-prefix Next Hop 47.0.0.0/8 LSR2 LSR1 LSR3 LSR2 IP Packet 47.80.55.3 Label Information Base: Label-In FEC Label-Out XX 47.0.0.0/8 17 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 3: LSR inserts label value into forwarding base 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

  15. LDP • Four Classes of messages • Discovery • Adjacency • Label Advertisement • Notification • Runs over TCP for all but Discovery • Easily Extensible Type/Length/Value (TLV) objects

  16. Discovery • Runs over UDP • LSR multicasts HELLO message to well known UDP port on “all routers on this subnet” multicast group • All routers listen to this group to learn all LSRs with direct connection • When an LSR is detected, a TCP LDP connection is established • The HELLO message can also be sent to a well-known UDP port at the IP address of a router if the IP address is known through static configuration.

  17. LDP Messages • INITIALIZATION- label allocation mode, timer values, range of labels to be used • KEEPALIVE- respond to Initialization of parameters are acceptable. Connection is terminated if timely keepalives are not received • LABEL MAPPING – Advertise a binding between adress prefix and label • LABEL WITHDRAWEL – reverse LABEL MAPPING, can occur because of routing changes • LABEL RELEASE • LABEL REQUEST • LABEL REQUEST ABORT

  18. LDP Messages • INITIALIZATION- • KEEPALIVE- • LABEL MAPPING – • LABEL RELEASE – Used in Conservative Label Retention mode • LABEL REQUEST – Used for down-stream-on-demand mode to request label mapping • LABEL REQUEST ABORT – If next hop changes so that the prior label request is invalid, this cancels the previous request

  19. Label Distribution - Methods Label Distribution can take place using one of two possible methods Unsolicited Downstream Label Distribution Downstream-on-Demand Label Distribution LSR2 LSR1 LSR2 LSR1 Label-FEC Binding Request for Binding • LSR2 and LSR1 are said to have an “LDP adjacency” (LSR2 being the downstream LSR) • 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 between 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 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

  20. DOWNSTREAM MODE MAKING SPF TREE COPY IN H/W #14 #311 #216 #99 #311 #963 #311 D #963 #14 #612 D #462 D D D #311 #99 #5 D D D

  21. DOWNSTREAM ON DEMAND MAKING SPF TREE COPY IN H/W #14 #311 #216 #99 #311 #963 #311 D D? D? #963 #14 D? D? #612 D D? #462 D D? D D #311 #99 #5 D D D D? D?

  22. Distribution Control: Ordered v. Independent Next Hop (for FEC) MPLS path forms as associations are made between FEC next-hops and incoming and outgoing labels Incoming Label Outgoing Label Independent LSP Control Ordered LSP Control • Label-FEC binding is communicated to peers if: • - LSR is the ‘egress’ LSR to particular FEC • - 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 • 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 Comparison Both methods are supported in the standard and can be fully interoperable

  23. Label Retention Methods Binding for LSR5 LSR2 An LSR may receive label bindings from multiple LSRs Some bindings may come from LSRs that are not the valid next-hop for that FEC LSR1 LSR5 Binding for LSR5 LSR3 Binding for LSR5 LSR4 Conservative Label Retention Liberal Label Retention LSR2 LSR2 Label Bindings for LSR5 Label Bindings for LSR5 LSR1 LSR1 LSR3 LSR3 LSR4’s Label LSR3’s Label LSR2’s Label LSR4’s Label LSR3’s Label LSR2’s Label LSR4 LSR4 Valid Next Hop Valid Next Hop • 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 • 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

  24. LIBERAL RETENTION MODE These labels are kept incase they are needed after a failure. #216 D D #963 #14 #622 #612 D #462 D D D D #311 #422 #99 #5 D D D

  25. CONSERVATIVE RETENTION MODE These labels are released the moment they are received. #216 D D #963 #14 #622 #612 D #462 D D D D #311 #422 #99 #5 D D D

  26. LDP - STATUS • Gone to last call • Multi Vendor interoperability demonstrated for DSOD on OC-3/ATM by (Nortel Networks & Cisco) at Interop/99 • Source code for these PDUs publicly available: www.NortelNetworks.com/mpls

  27. Label Distribution Protocols • Overview of Hop-by-hop & Explicit • Label Distribution Protocol (LDP) • Constraint-based Routing LDP (CR-LDP)

  28. Constraint-based LSP Setup using LDP • Uses LDP Messages (request, map, notify) • Shares TCP/IP connection with LDP • Can coexist with vanilla LDP and inter-work with it, or can exist as an entity on its own • Introduces additional data to the vanilla LDP messages to signal ER, and other “Constraints”

  29. 2. Request message processed and next node determined. Path list modified to <C,D> 3. Request message terminates. 1. Label Request message. It contains ER path < B,C,D> 6. When LER A receives label mapping, the ER established. 5. LSR C receives label to use for sending data to LER D. Label table updated 4. Label mapping message originates. ER-LSP Setup using CR-LDP LER A LSR B LSR C LER D ER Label Switched Path Ingress Egress

  30. LDP/CR-LDP INTERWORKING INSERT ER{A,B,C} #216 #99 #311 #14 #612 #462 #5 A B C LDP CR-LDP - It is possible to take a vanilla LDP label request let it flow vanilla to the edge of the core, insert an ER hop list at the core boundary at which point it is CR-LDP to the far side of the core.

  31. Basic LDP Message additions • LSPID: A unique tunnel identifier within an MPLS network. • ER: An explicit route, normally a list of IPV4 addresses to follow (source route) the label request message. • Resource Class (Color): to constrain the route to only links of this Color. Basically a 32 bit mask used for constraint based computations. • Traffic Parameters: similar to ATM call setup, which specify treatment and reserve resources.

  32. CR-LDP Traffic Parameters

  33. CRLSP characteristics not edge functions • The approach is like diff-serv’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

  34. 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

  35. 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

  36. 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

  37. 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 a 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

  38. Weight • Specifies the CRLSP’s weight in the “realtive 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

  39. Negotiation flags

  40. CR-LDP PREEMPTION A CR-LSP carries an LSP priority. This priority can be used to allow new LSPs to bump existing LSPs of lower priority in order to steal their resources. This is especially useful during times of failure and allows you to rank the LSPs such that the most important obtain resources before less important LSPs. These are called the setupPriority and a holdingPriority and 8 levels are provided.

  41. CR-LDP PREEMPTION When an LSP is established its setupPriority is compared with the holdingPriority of existing LSPs, any with lower holdingPriority may be bumped to obtain their resources. This process may continue in a domino fashion until the lowest holdingPriority LSPs either clear or are on the worst routes.

  42. PREEMPTION A.K.A. BUMPING Route={A,B,C} #216 #14 #972 #462 B C A

  43. Label Distribution Protocols • Overview of Hop-by-hop & Explicit • Label Distribution Protocol (LDP) • Constraint-based Routing LDP (CR-LDP) • Extensions to RSVP

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

  45. Traffic EngineeringCurrent IGP’s lead to Hyper-Aggregation TRAFFIC FOR D SHORTEST PATH ROUTED 9 UNDER ULTILIZED] 4 OVERUTILIZED ] LINKS D S MASSIVE CONGESTION CONGESTION

  46. 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

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

  48. Benefit of MPLS traffic engineering • Traffic engineering in large IP networks currently uses ATM. • The router network is ATM unaware and hence there are two control planes. • The router control plane has a large number of adjacencies which limits scalability. • MPLS is IP aware and introduces a single IP control plane that matches the physical topology and hence scales better and is simpler. • This is being extended into MPS (MPLambdaS) to extend Traffic Engineering to the emerging Optical networking plane

  49. 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

  50. Benefits of MPLS QoS • The ultimate benefit is a unified or converged network supporting all classes of service • The IP Qos model for the support of real time services such as voice is at an early stage. • Most multi-service networks are moving to a “Ships-in-the-night” paradigm • This continues to support ATM services with ATM protocols • And at the same time on the same platforms supports and MPLS control plane of IP services

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