MPLS Protection/Restoration

1. MPLS Protection/Restoration Instructor : Dr.Qiao Ph.d Student: Ming Zhao HanSheng Lei Hlei@buffalo.edu Mingzhao@acsu.buffalo.edu

2. Multiprotocol Label Switching Architecture & LDP Introduction MPLS Basics LDP Procedures LDP Specification

3. MPLS&LDP->Introduction • Conventional network forwarding Each router analyzes the coming packet’s header and independently chooses a next hop. Routing algorithm and adequate speed are prerequisite. • MPLS forwarding All forwarding is driven by the labels, no header analysis needed. Once a packet enters a network, it’s assigned a label. Each router forwards packets according their labels.

4. MPLS&LDP->Introduction • Advantages over conventional routing • Router can use any information in determining label assignment, not limited to packet header; • How to distribute labels may become more and more complicated, without any impact on the routers that merely forward labeled packets. • A label can be used to represent a pre-chosen route so that the identity of explicit route need not be carried with the packet. • Mutiprotocol: its techniques are applicable to ANY network layer protocol. • Etc.

5. MPLS&LDP->Introduction • Terminology. Some important terms. FEC(forwarding equivalence class) a group of IP packets which are forwarded in the same manner (e.g., over the same path, with the same forwarding treatment) LSR(label switching router) an MPLS node which is capable of forwarding native Layer 3 packets label swap the basic forwarding operation consisting of looking up an incoming label to determine the outgoing label, encapsulation, port, and other data handling information. MPLS domain a contiguous set of nodes which operate MPLS routing and forwarding and which are also in one Routing or Administrative Domain

6. MPLS&LDP->MPLS Basics • Labels • Packet forward • Route selection • Tunnels and Hierarchy • Multiprotocol

7. MPLS&LDP->MPLS Basics->Labels A label is a short, fixed length, locally significant identifier which is used to identify a FEC. The label which is put on a particular packet represents the FEC to which that packet is assigned. Most commonly, a packet is assigned to a FEC based (completely or partially) on its network layer destination address. However, the label is never an encoding of that address.

8. Ru Rd MPLS&LDP->MPLS Basics->Labels Upstream LSR Downstream LSR Agreement: "binding" label L to FEC F for packets moving from Ru to Rd. So, L becomes Ru's "outgoing label" representing FEC F, and L becomes Rd's "incoming label" representing FEC F. Note that L is an arbitrary value whose binding to F is local to Ru and Rd.

9. MPLS&LDP->MPLS Basics->Labels • Label Assignment and Distribution The decision to bind a particular label L to a particular FEC F is made by the LSR which is DOWNSTREAM with respect to that binding. The downstream LSR then informs the upstream LSR of the binding. • Attributes of a Label Binding A particular binding of label L to FEC F, distributed by Rd to Ru, may have associated "attributes". If Ru, acting as a downstream LSR, distributes a binding of a label to FEC F, then under certain conditions, it may be required to also distribute the corresponding attribute that it received from Rd.

10. MPLS&LDP->MPLS Basics->Labels • A label distribution protocol is a set of procedures by which one LSR informs another of the label/FEC bindings it has made. • The label distribution protocol also encompasses any negotiations in which two label distribution peers need to engage in order to learn of each other's MPLS capabilities. • THE ARCHITECTURE DOES NOT ASSUME THAT THERE IS ONLY A SINGLE LABEL DISTRIBUTION PROTOCOL. E.g., [MPLS-BGP], [MPLS-RSVP], [MPLS-RSVP-TUNNELS], [MPLS-LDP], [MPLS-CR-LDP].

11. Examine the label of packet Unlabeled labeled Determine FEC Invalid label ILM Discard No outgoing label NHLFE FTN Next Hop MPLS&LDP->MPLS Basics->Packet forward Fig 1. Procedures to forward a packet

12. MPLS&LDP->MPLS Basics-> Packet forward • ILM(Incoming Label Map) Maps each incoming label to a set of NHLFEs. • NHLFE(Next Hop Label Forwarding Entry) It contains the following information: 1. the packet's next hop 2. the operation to perform on the packet's label stack; this is one of the following operations: a) replace the label at the top of the label stack with a specified new label b) pop the label stack c) replace the label at the top of the label stack with a specified new label, and then push one or more specified new labels onto the label stack. It may also contain some other information

13. MPLS&LDP->MPLS Basics-> Packet forward • FTN(FEC-to-NHLFE) The FTN maps each FEC to a set of NHLFEs. It is used when forwarding packets that arrive unlabeled, but which are to be labeled before being forwarded. • Determine unlabeled packet’s FEC LSR analyzes the layer network header to make decision. How to analyze is beyond the scope of architecture.

14. MPLS&LDP->MPLS Basics-> Packet forward • Invalid Incoming Labels when a labeled packet is received with an invalid incoming label, it MUST be discarded, UNLESS it is determined by some means (not within the scope of the MPLS architecture) that forwarding it unlabeled cannot cause any harm. • Lack of Outgoing Label Unless it can be determined that neither of these situations obtains, the only safe procedure is to discard the packet. - If the packet has been following an explicitly routed LSP, this could result in a loop. -The packet's network header may not contain enough information to enable this particular LSR to forward it correctly.

15. MPLS&LDP->MPLS Basics-> Packet forward

16. MPLS&LDP->MPLS Basics-> Packet forward

17. MPLS&LDP->MPLS Basics-> Route selection • Hop by hop routing Allows each node to independently choose the next hop for each FEC. This is the usual mode today in existing IP networks. A "hop by hop routed LSP" is an LSP whose route is selected using hop by hop routing. • Explicit routing A single LSR, generally the LSP ingress or the LSP egress, specifies several (or all) of the LSRs in the LSP. Explicit routing may be useful for a number of purposes, such as policy routing or traffic engineering.

18. MPLS&LDP->MPLS Basics-> Route selection

19. R3 R4 R1 R2 R21 R22 R23 MPLS&LDP->MPLS Basics-> Tunnels&Hierarchy Level m-1 Level m Fig. 2. Tunnels and Hierarchy

20. MPLS&LDP->MPLS Basics-> Tunnels&Hierarchy • Hop-by-Hop Routed Tunnel If a Tunneled Packet follows the Hop-by-hop path from Ru to Rd, we say that it is in an "Hop-by-Hop Routed Tunnel" whose "transmit endpoint" is Ru and whose "receive endpoint" is Rd. • Explicitly Routed Tunnel If a Tunneled Packet travels from Ru to Rd over a path other than the Hop-by-hop path, we say that it is in an "Explicitly Routed Tunnel" whose "transmit endpoint" is Ru and whose "receive endpoint" is Rd. For example, we might send a packet through an Explicitly Routed Tunnel by encapsulating it in a packet which is source routed.

21. MPLS&LDP->MPLS Basics->Multiprotocol • Labels for RSVP When RSVP is used to set up resource reservations for particular flows, it can be desirable to label the packets in those flows, so that the RSVP does not need to be applied at each hop. It can be argued that having RSVP distribute the labels as part of its path/reservation setup process is the most efficient method of distributing labels for this purpose.

22. MPLS&LDP->MPLS Basics->Multiprotocol • Labels for Explicitly Routed LSPs In some applications of MPLS, particularly those related to traffic engineering, it is desirable to set up an explicitly routed path, from ingress to egress. It is also desirable to apply resource reservations along that path. One can imagine two approaches to this: - Start with an existing protocol that is used for setting up resource reservations, and extend it to support explicit routing and label distribution. - Start with an existing protocol that is used for label distribution, and extend it to support explicit routing and resource reservations.

23. MPLS&LDP->LDP Procedures • The Procedures for Advertising and Using labels There are a number of different procedures that may be used to distribute label bindings. The downstream LSR must perform: - The Distribution Procedure, and - the Withdrawal Procedure. The upstream LSR must perform: - The Request Procedure, and - the NotAvailable Procedure, and - the Release Procedure, and - the labelUse Procedure.

24. MPLS&LDP->LDP Procedures • Downstream LSR: Distribution Procedure The Distribution Procedure is used by a downstream LSR to determine when it should distribute a label binding for a particular address prefix to its label distribution peers. 2. Upstream LSR: Request Procedure The Request Procedure is used by the upstream LSR for an address prefix to determine when to explicitly request that the downstream LSR bind a label to that prefix and distribute the binding.

25. MPLS&LDP->LDP Procedures 3. Upstream LSR: Release Procedure Suppose that Rd is an LSR which has bound a label to address prefix X, and has distributed that binding to LSR Ru. If Rd does not happen to be Ru's L3 next hop for address prefix X, or has ceased to be Ru's L3 next hop for address prefix X, then Ru will not be using the label. The Release Procedure determines how Ru acts in this case. 4. Upstream LSR: labelUse Procedure Suppose Ru is an LSR which has received label binding L for address prefix X from LSR Rd, and Ru is upstream of Rd with respect to X. Ru will make use of the binding if Rd is Ru's L3 next hop for X. The labelUse Procedure determines just how Ru makes use of Rd's binding.

26. MPLS&LDP->LDP Procedures • Security Considerations Some routers may implement security procedures which depend on the network layer header being in a fixed place relative to the data link layer header. The MPLS generic encapsulation inserts a shim between the data link layer header and the network layer header. This may cause any such security procedures to fail. An MPLS label has its meaning by virtue of an agreement between the LSR that puts the label in the label stack, and the LSR that interprets that label (the "label reader"). If labeled packets are accepted from untrusted sources, or if a particular incoming label is accepted from an LSR to which that label has not been distributed, then packets may be routed in an illegitimate manner.

27. MPLS&LDP->LDP specification • LDP Message Exchange • LDP Operation • LDP Discovery • LDP Session

28. MPLS&LDP->LDP specification-> Message Exchange • Discovery messages used to announce and maintain the presence of an LSR in a network. • Session messages used to establish, maintain, and terminate sessions between LDP peers. • Advertisement messages used to create, change, and delete label mappings for FECs. • Notification messages used to provide advisory information and to signal error information.

29. MPLS&LDP-> 5. LDP specification-> LDP Operation • FECs Each FEC is specified as a set of one or more FEC elements. Each FEC element identifies a set of packets which may be mapped to the corresponding LSP. 1. Address Prefix. This element is an address prefix of any length from 0 to a full address, inclusive. 2. Host Address. This element is a full host address.

30. MPLS&LDP-> 5. LDP specification-> LDP Operation • Label Spaces The notion of "label space" is useful for discussing the assignment and distribution of labels. - Per interface label space. Interface-specific incoming labels are used for interfaces that use interface resources for labels. An example of such an interface is a label-controlled ATM interface that uses VCIs as labels. - Per platform label space. Platform-wide incoming labels are used for interfaces that can share the same labels.

31. MPLS&LDP-> 5. LDP specification-> LDP Operation • LDP Identifiers An LDP identifier is a six octet quantity used to identify an LSR label space. The first four octets identify the LSR and must be a globally unique value, such as a 32-bit router Id assigned to the LSR. The last two octets identify a specific label space within the LSR. The last two octets of LDP Identifiers for platform-wide label spaces are always both zero. <LSR Id> : <label space id> e.g., lsr171:0, lsr19:2.

32. MPLS&LDP-> 5. LDP specification-> LDP Operation • LDP Sessions LDP sessions exist between LSRs to support label exchange between them. When an LSR uses LDP to advertise more than one label space to another LSR it uses a separate LDP session for each label space. • LDP Transport LDP uses TCP as a reliable transport for sessions. When multiple LDP sessions are required between two LSRs there is one TCP session for each LDP session.

33. MPLS&LDP-> 5. LDP specification-> LDP Operation

34. MPLS&LDP-> 5. LDP specification-> LDP Discovery LDP discovery is a mechanism that enables an LSR to discover potential LDP peers. Discovery makes it unnecessary to explicitly configure an LSR's label switching peers. - A basic discovery mechanism used to discover LSR neighbors that are directly connected at the link level. - An extended discovery mechanism used to locate LSRs that are not directly connected at the link level.

35. MPLS&LDP-> 5. LDP specification-> LDP Discovery • Extended Discovery Mechanism LDP sessions between non-directly connected LSRs are supported by LDP Extended Discovery. Extended Discovery differs from Basic Discovery in the following ways: - A Targeted Hello is sent to a specific address - Unlike Basic Discovery, which is symmetric, Extended Discovery is asymmetric. Targeted LSR decides whether to respond to or ignore the Targeted Hello.

36. MPLS&LDP-> 5. LDP specification-> LDP Session • Session Establishment The exchange of LDP Discovery Hellos between two LSRs triggers LDP session establishment. Session establishment is a two step process: - Transport connection establishment. - Session initialization

37. NON EXISTENT Time out/Error Time out/Error ACTIVE ROLE INITIALIZED PASSIVE Time out/Error Keep Alive OPENREC OPENSENT Keep Alive Shut Down/Time out OPERATIONAL MPLS&LDP-> 5. LDP specification-> LDP Session Fig.3 Session Initialization State Machine

38. Outline • Introduction • MPLS Recovery Framework • MPLS Mechanism for Protection/Restoration • Shared Backup LSP Restoration • Fast reroute • RSVP-TE Recovery • A Heuristic Restoration Approach • Analysis • Simulations • Comparison

39. Outline • Introduction • MPLS Recovery Framework • MPLS Mechanism for Protection/Restoration • Shared Backup LSP Restoration • Fast reroute • RSVP-TE Recovery • A Heuristic Restoration Approach • Analysis • Simulations • Comparison

40. Current Backbone Networks Protection • Link layer protection (SONET/SDH) • Be capable of service restoration within few tens of milliseconds • The scope of the protection is limited, has no visibility into higher layer operations • Layer 3 protection • Routing protocol provide much greater flexibility • The cost of the restoration time in the order of seconds to minutes

41. Motivation: MPLS-Based Recovery • MPLS is the lowest layer with the knowledge of the entire network topology • MPLS provide necessary traffic engineering capabilities • MPLS has desirable attributes when applied to the purpose of recovery for connectionless networks • MPLS provide restoration times significantly shorter then the convergence times of IP routing protocols

42. Definitions and Terminology • Rerouting the recovery path or path segments are created dynamically after the detection of a fault on the working path. (the recovery path is not pre-established) • Protection Switching In contrast the Rerouting, the recovery path is pre- established

43. Definitions and Terminology • Path Switch LSR (PSL) • The PSL is responsible for switching or replicating the traffic between the working path and the recovery path • Normally chose as the Ingress LSR or the nearest upstream LSR upon the failure node • Path Merge LSR (PML) • The PML is responsible for receiving the recovery path traffic, and either merges the traffic back onto the working path, or, if it is itself the destination, passes the traffic on to the higher layer protocols • Normally chose as the Egress LSR

44. Definitions and Terminology • Fault Indication Signal (FIS) A signal that indicates that a fault along a path has occurred. It is relayed by each intermediate LSR to its upstream or downstream neighbor, until it reaches the PSL • Fault Recovery Signal (FIS) A signal that indicates a fault along a working path has been repaired.Like the FIS,it is relayed by each intermediate LSR to its upstream or downstream neighbor, until is reaches the PSL

45. Fault Detection • Path Failure detected by a link probing mechanism (hello liveness message ) between neighbor LSRs • Path Degraded path has connectivity, but that the quality of the connection is unacceptable (eg.high error bit rate, label mismatch or due to TTL errors). it is detected by a path performance monitoring mechanism • Link Failure • Link Degraded the link over which the working path is carried is performing below an acceptable level

46. Path Mapping • Path Mapping : the methods of mapping traffic from a faulty working path on to the recovery path • 1-to-1 Protection recovery path that is only to be used to recover that specific working path • n-to-1 Protection n working paths are protected using only one recovery path • n-to-m Protection n working paths are protected using m recovery paths, the n working paths and the m recovery paths should be diversely routed between the same PSL and PML

47. Scope of Recovery • Local Repair • protect against a link or neighbor node fault and to minimize the amount of time required for failure propagation • Fast but not optimized • Global Repair • the PSL is usually distant from the failure and needs to be notified by a FIS • the recovery path can be made completely link and node disjoint with its working path • slower than local repair

48. Post Recovery Operation • When traffic is flowing on the recovery path decisions can be made to whether let the traffic remain on the recovery path and consider it as: • a new working path (Non-Revertive Mode ) • switch to the old (Revertive Mode ) • switch to a new preferred working path ( make before break ----- RSVP TE Recovery)

49. Outline • Introduction • MPLS Recovery Framework • MPLS Mechanism for Protection/Restoration • Shared Backup LSP Restoration • Fast reroute • RSVP-TE Recovery • A Heuristic Restoration Approach • Analysis • Simulations • Comparison

50. MPLS-based Recovery Principles • Configuration of Recovery • Default-recovery (No MPLS-based recovery enabled) • Recoverable (MPLS-based recovery enabled) • Initiation of Path Setup • Pre-established • Pre Qualified • Established-on-Demand • Initiation of Resource Allocation • Pre-reserved • Reserved-on-Demand