1、Advanced Topics in Networking: MPLS and GMPLS,Hang Liu Thomson Inc., Corporate Research Lab Princeton, NJ,Note: Thank Dr. Debanjan Saha for the teaching materials on MPLS,MPLS: Multi-protocol Label Switching,3,Topics,Introduction History and motivation MPLS mechanisms MPLS protocols RSVP-TE/CR-LDP M
2、PLS applications VPNSs, traffic engineering, restoration,4,WHY MPLS ?,Ultra fast forwarding Use switching instead of routing IP Traffic Engineering Constraint-based routing Virtual Private Networks Controllable tunneling mechanism Protection and restoration,5,IP Forwarding Table,47.1.*.*,47.2.*.*,47
3、.3.*.*,1,2,3,1,2,1,2,3,6,Hop-by-Hop IP Forwarding,47.1,47.2,47.3,1,2,3,1,2,1,2,3,IP 47.1.1.1,IP 47.1.1.1,IP 47.1.1.1,7,Routing Lookup,Longest prefix match is (was) expensive. Label matching is much less expensive.,9.1.*.*,67.1.2.2,4,9.1.1.*,113.1.2.1,8,9.1.1.1,71.1.2.3,6,9.2.1.1,71.1.2.3,6,Prefix,Ne
4、xt Hop,Interface,8,MPLS Labels,47.1,47.2,47.3,1,2,3,1,2,1,2,3,3,9,Label Switched Path,47.1,47.2,47.3,1,2,3,1,2,1,2,3,3,10,Forwarding Equivalence Classes,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 scalabil
5、ity In conventional routing, a packet is assigned to a FEC at each hop (i.e. L3 look-up), in MPLS it is only done once at the network ingress,Packets are destined for different address prefixes, but can be mapped to common path,LSR,LSR,LER,LER,LSP,11,MPLS Terminology,LDP: Label Distribution Protocol
6、 LSP: Label Switched Path FEC: Forwarding Equivalence Class LSR: Label Switching Router LER: Label Edge Router,12,Label Distribution Methods,LSR1,LSR2,Downstream Label Distribution,Label-FEC Binding,LSR2 discovers a next hop for a particular FECLSR2 generates a label for the FEC and communicates the
7、 binding to LSR1LSR1 inserts the binding into its forwarding tablesIf LSR2 is the next hop for the FEC, LSR1 can use that label knowing that its meaning is understood,LSR1,LSR2,Downstream-on-Demand Label Distribution,Label-FEC Binding,LSR1 recognizes LSR2 as its next-hop for an FECA request is made
8、to LSR2 for a binding between the FEC and a labelIf LSR2 recognizes the FEC and has a next hop for it, it creates a binding and replies to LSR1Both LSRs then have a common understanding,Request for Binding,Both methods are supported, even in the same network at the same time,13,Distribution Control,
9、Independent LSP Control,Ordered LSP Control,Next Hop (for FEC),Outgoing Label,Incoming Label,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 ou
10、tgoing 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 LSRLSP formation flows from egress to ingress,Definition,Comparison,Labels can be exchanged with less delay Does not depend on ava
11、ilability 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 fro
12、m loops Used for explicit routing and multicast,Both methods are supported in the standard and can be fully interoperable,14,Label Retention Methods,Liberal Label Retention,Conservative Label Retention,LSR1,LSR2,LSR3,LSR4,Label Bindings for LSR4,ValidNext Hop,LSR4s Label LSR3s Label LSR2s Label,LSR1
13、,LSR2,LSR3,LSR4,Label Bindings for LSR4,ValidNext Hop,LSR4s Label LSR3s Label LSR2s Label,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
14、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 sp
15、eed of adaptation to routing changes,15,Label Encapsulation,ATM,FR,Ethernet,PPP,MPLS Encapsulation is specified over various media types. Top labels may use existing format, lower label(s) use a new “shim” label format.,VPI,VCI,DLCI,“Shim Label”,L2,Label,“Shim Label” .,IP | PAYLOAD,16,Label Format,E
16、xp field used to identify the class of service Stack bit is used identify the last label in the label stack TTL field is used as a time-to-live counter. Special processing rules are used to mimic IP TTL semantics.,Label 20 bits,Exp 3 bits,Stack 1 bit,TTL 8 bits,17,Label Distribution Protocols,Label
17、Distribution Protocol (LDP) Constraint-based Routing LDP (CR-LDP) Extensions to RSVP Extensions to BGP,18,LDP:Label Distribution Protocol,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 LSR2,LSR1,LSR2,LSR3,IP Pac
18、ket,47.80.55.3,Routing Table:Addr-prefix Next Hop 47.0.0.0/8 LSR3,For 47.0.0.0/8 use label 17,Label Information Base:Label-In FEC Label-Out 17 47.0.0.0/8 XX,Label Information Base:Label-In FEC Label-Out XX 47.0.0.0/8 17,Step 1: LSR creates binding between FEC and label value,Step 2: LSR communicates
19、 binding to adjacent LSR,Step 3: LSR inserts label value into forwarding base,Common understanding of which FEC the label is referring to!,19,LDP: Basic Characteristics,Provides LSR discovery mechanisms to enable LSR peers to find each other and establish communicationDefines four classes of message
20、s DISCOVERY: deals with finding neighboring LSRs ADJACENCY: deals with initialization, keep alive, and shutdown of sessions LABEL ADVERTISEMENT: deals with label binding advertisements, request, withdrawal, and release NOTIFICATION: deals with advisory information and signal error information Runs o
21、ver TCP for reliable delivery of messages, except for discovery, which uses UDP and IP multicast Designed to be extensible, using messages specified as TLVs (type, value, length) encoded objects.,20,LDP Messages,INITIALIZATION KEEPALIVE LABEL MAPPING LABEL WITHDRAWAL LABEL RELEASE LABEL REQUEST,21,4
22、7.1,47.2,47.3,1,2,3,1,2,1,2,3,3,Explicitly Routed LSP,22,ER LSP - Advantages,Operator has routing flexibility policy-based, QoS-based Can use routes other than shortest path Can compute routes based on constraints in exactly the same manner as ATM based on distributed topology database.(traffic engi
23、neering),23,ER LSP - discord!,Two signaling options proposed in the standards: CR-LDP, RSVP extensions:CR-LDP = LDP + Explicit RouteRSVP ext = Traditional RSVP + Explicit Route +Scalability Extensions Market will probably have to resolve it Survival of the fittest not such a bad thing.,24,MPLS and Q
24、oS in IP Network,Integrated Services Differentiated Services,25,Integrated Services Internet,Applications specify traffic and service specs Tspec: traffic specs including peak rate, maximum packet size, burst size, and mean rate Rspec: service spec, specifically service rate Two classes of service d
25、efined Guaranteed service: satisfies hard guarantees on bandwidth and delay Controlled load service: provides service similar to that in “unloaded network” RSVP was extended to RSVP-TE support signaling RSVP was further extend to add MPLS support,26,Differentiated Services Internet,IP packets carry
26、6-bit service code points (DSCP) Potentially support 64-different classes of services Routers map DSCP to per-hop-behavior (PHB) PHBs can be standard or local Standard PHBs include Default: No special treatment or best effort Expedited forwarding (EF): Low delay and loss Assured forwarding (AF): Mul
27、tiple classes, each class with multiple drop priorities LSRs dont sort based on IP headers, hence DSCPs need to be mapped to EXP field in MPLS shim header Exp field is only 3-bit wide can support only 8 DSCPs/PHBs Labels can be used if more than 8 PHBs need to be supported Same approach can be used
28、for link layers which do not use Shim headers, e.g. ATM,27,Traffic Engineering with RSVP,Sender,Receiver,PATH Tspec,RESV Rspec,PATH Tspec,PATH Tspec,PATH Tspec,RESV Rspec,RESV Rspec,RESV Rspec,28,Label Distribution with RSVP-TE,PATH Tspec,RESV Rspec Label = 5,RESV Rspec Label = 10,Sender,PATH Tspec,
29、RESV Rspec,PATH Tspec,PATH Tspec,PATH Tspec,RESV Rspec,29,MPLS Protection,End-to-end protection Fast node and link reroute,30,MPLS Protection End-to-end Path Protection,A,C,B,D,E,F,Backup LSP,Primary LSP,Backup and primary LSPs should be route diverse,31,MPLS Protection: Fast Reroute,LSR A,LSR F,LSR
30、 E,LSR D,LSR C,LSR B,Detour to avoid AB,Detour to avoid BC,Detour to avoid CD,Detour to avoid DE,Detour to avoid link DE,Detour around node or link failures Example LSP shown traverses (A, B, C, D, E, F) Each detour avoids Immediate downstream node & link towards it Except for last detour: only avoi
31、ds link DE,32,Detour Merging,LSR A,LSR F,LSR E,LSR D,LSR C,LSR B,Detour to avoid AB,Detour to avoid BC,Merged detour to avoid AB and BC,Reduces state maintainedImproves resource utilization,33,MPLS Protection Types,1+1: Backup LSP established in advance, resources dedicated, data simultaneously sent
32、 on both primary and backup Switchover performed only by egress LSR Fastest, but most resource intensive 1:1 : Same as 1+1 with the difference that data is not sent on the backup Requires failure notification to the ingress LSR to start transmitting on backup Notification may be send to egress also
33、Resources in the backup may be used by other traffic Low priority traffic (e.g., plain IP traffic), shared by other backup paths,34,MPLS VPN: The Problem,10.1/16,10.1/16,10.2/16,10.2/16,10.3/16,10.3/16,Provider Network,Customer 1 Site 1,Customer 1 Site 2,Customer 1 Site 3,Customer 2 Site 3,Customer
34、2 Site 1,Customer 2 Site 2,35,MPLS VPN: The Model,10.1/16,10.1/16,10.2/16,10.2/16,10.3/16,10.3/16,Customer 1 Site 1,Customer 2 Site 1,Customer 2 Site 3,Customer 1 Site 3,Customer 2 Site 2,Customer 1 Site 2,Customer 1 Virtual Network,Customer 2 Virtual Network,36,MPLS VPN: The Solution,10.1/16,10.1/1
35、6,10.2/16,10.2/16,10.3/16,10.3/16,Customer 1 Site 1,Customer 1 Site 2,Customer 1 Site 3,Customer 2 Site 3,Customer 2 Site 1,Customer 2 Site 2,VRF 1,VRF 1,VRF 1,VRF 2,VRF 2,VRF 2,MPLS LSP,MPLS LSP,GMPLS: Generalized MPLS & ASON: Automatically Switched Optical Network,38,Outline,ASON Control Plane Sta
36、ndards UNI and NNI Protection and Restoration,39,Traditional Management Plane for Optical Transport Networks,A lot of manual operations Integration of different EMS and NMS is complex multiple types of equipment from different vendors with different technologies Automatic end-to-end provisioning is
37、not easy planning, path computation, connection establishment,40,Distributed Control Plane,Distributed control plane offers automatic neighbor and topology discovery automatic end-to-end provisioning and connection modification scalability and interoperability unified traffic engineering and protect
38、ion/restoration In an environment where IP router networks are interconnected via a mesh optical network,41,ASON Control Plane,Goals of ASON control plane Facilitate configuration of connections within an optical transport network in a reliable, efficient, scalable, interoperable and automatic way S
39、witched connection (SC): requested by a user Soft permanent connection (SPC): initiated by the management plane Good for applications required for dynamic circuits (holding time provisioning time) Allow reconfiguring or modifying connections for existing calls Perform protection and restoration func
40、tion,42,ASON Control Plane Components,Components of ASON control plane Call Controller Connection Controller Link Resource Manager Routing Controller Discovery Agent Termination and Adaptation Performer Etc.,43,Related Standard Bodies,ITU ASON Architecture and Components UNI and NNI interfaces IETF
41、Generalized GMPLS Protocols Extends MPLS/IP protocols based on generalized interface requirements signaling (RSVP-TE and CR-LDP with GMPLS extensions) routing (OSPF-TE and IS-IS with GMPLS extensions) link management and neighbor discovery (LMP) OIF Focuses on application of IETF protocols in an ove
42、rlay model Generates implementation agreements UNI and NNI,44,GMPLS: Generalized MPLS,GMPLS Handles Nodes With Diverse Capabilities. Packet Switch Capable (PSC) Time Division Multiplexing Capable (TDM) Lambda Switch Capable (LSC) Fiber Switch Capable (FSC) Each Node Is Treated As an MPLS Label-switc
43、hing Router (LSR) Lightpaths/TDM Circuits Are Considered Similar to Label-Switched Paths (LSPs) Selection of s and OXC ports are considered similar to selection of labels,FSC Cloud,LSC Cloud,TDM Cloud,PSC Cloud,45,Overview of IETF GMPLS Protocols,GMPLS-based distributed control plane automatic servi
44、ce provisioning (signaling) dynamic network topology and resource availability dissemination (routing) neighbor discovery and link management (link management),46,Control Channel,Bi-directional channel is required between two logically or physically adjacent nodes to exchange control messages in-ban
45、d with data (such as two IP routers, SONET overhead bytes) out-of-band through a separate link or even separate network (such as an IP network) de-couple data channel and control channel one control channel to one or multiple data channels,47,Connection Provisioning through GMPLS,Connection request
46、received from a client or a management agent at ingress node Ingress node computes the explicit route from ingress to egress node take into account a set of constraints (bandwidth requirements, resource availability, protection/restoration and traffic engineering constraints) Require routing protoco
47、l to disseminate network topology and link state information Signaling the connection establishment along the path RSVP-TE or CR-LDP extension,Ingress Node (A),Egress Node (B),Request,48,Signaling Protocol,Establishes and deletes paths LSP setup: label request and resource reservation/allocation LSP
48、 deletion: label and resource release GMPLS Signaling Extends MPLS label semantics to accommodate fiber, waveband, lambda, TDM and packet-capable LSP establishment Extends RSVP-TE and CR-LDP for carrying the generalized label objects over explicit path Supports bi-directional LSP setup Suggested Lab
49、el Upstream node suggests a label to downstream node for speeding up configuration Label Set Limit the labels what downstream node can choose from,49,Routing Protocol,Disseminates network topology and link resource availability over control channel (CC) Manages the link state database and routing ta
50、bles make routing decision Provides path computation algorithm with the routing information to obtain explicit route Traffic engineering (TE) and GMPLS routing extensions Extends OSPF or IS-IS Support multiple types of GMPLS TE links Carry new link attributes TE LSA database for explicit path computation,
