1. Jan 29, 2006Lahore University of Management Sciences1 Seamless Detection of Link and Node Failures for Local Protection in MPLS Zartash Afzal Uzmi Computer Science and Engineering Lahore University of Management Sciences (LUMS)

2. Jan 29, 2006Lahore University of Management Sciences2 Outline Background Forwarding and Routing in IP and MPLS Networks Network Service Requirements Protection Routing in MPLS Terminology: Types of Backup Paths Backup Bandwidth Sharing Activation sets Failures and Backup Path Activation Distinguishable Failure Events: Ideal Case Actual Failures Control Plane Mechanism Outline of Proof

3. Jan 29, 2006Lahore University of Management Sciences3 Outline Background Forwarding and Routing in IP and MPLS Networks Network Service Requirements Protection Routing in MPLS Terminology: Types of Backup Paths Backup Bandwidth Sharing Activation sets Failures and Backup Path Activation Distinguishable Failure Events: Ideal Case Actual Failures Control Plane Mechanism Outline of Proof

4. Jan 29, 2006Lahore University of Management Sciences4 Forwarding and Routing Forwarding: Passing a packet to the next hop router Routing: Computing the “best” path to the destination IP routing – includes routing and forwarding Each router makes the routing decision Each router makes the forwarding decision IP routing is hop-by-hop MPLS routing Only one router (source) makes the routing decision Intermediate routers make the forwarding decision An MPLS path or “virtual circuit” from source to destination is created and is called an LSP (label switched path)

5. Jan 29, 2006Lahore University of Management Sciences5 Network Service Requirements Bandwidth Guaranteed Primary Paths MPLS can establish bandwidth-guaranteed paths Bandwidth Guaranteed Backup Paths BW remains provisioned in case of network failure Two options for recovery from network failure: Compute backup paths AFTER failures occur Compute and install PRESET backup paths Minimal “Recovery Latency” Recovery latency is the time that elapses between: “the occurrence of a failure”, and “the diversion of network traffic on a new path” Preset backup paths needed for minimal latency

6. Jan 29, 2006Lahore University of Management Sciences6 Outline Background Forwarding and Routing in IP and MPLS Networks Network Service Requirements Protection Routing in MPLS Terminology: Types of Backup Paths Backup Bandwidth Sharing Activation sets Failures and Backup Path Activation Distinguishable Failure Events: Ideal Case Actual Failures Control Plane Mechanism Outline of Proof

7. Jan 29, 2006Lahore University of Management Sciences7 Protection in MPLS: Preset Backup Paths S123D Primary Path Backup Path Path Protection This type of “path Protection” takes 100s of ms. We need “Local Protection” to quickly switch onto backup paths! Local Protection

8. Jan 29, 2006Lahore University of Management Sciences8 nhop and nnhop paths Primary Path Backup Path All links and all nodes are protected! AB C D E PLR: Point of Local Repair nnhop nhop LOCAL PROTECTION (showing one LSP only)  nhop protects link only, e.g., (D,E)  nnhop protects link (C,D) and node (D)

9. Jan 29, 2006Lahore University of Management Sciences9 Opportunity cost of backup paths Protection requires that backup paths are setup in advance Upon failure, traffic is promptly switched onto preset backup paths Bandwidth must be reserved for all backup paths This results in a reduction in the number of Primary LSPs that can otherwise be placed on the network Can we reduce the amount of “backup bandwidth” but still provide guaranteed backups? YES: Try to share the bandwidth along backup paths

10. Jan 29, 2006Lahore University of Management Sciences10 BW Sharing in backup Paths Example: max(X, Y) BW: Y AB CD E F G LSP1 LSP2 BW: X Primary Path Backup Path X X X YY X+YX+Y Sharing is possible IF Links (A,B) and (C,D) do not simultaneously fail!

11. Jan 29, 2006Lahore University of Management Sciences11 Activation Sets A B C D E Activation set for node BActivation set for link (A,B) A B C D E Can backup paths always share the bandwidth? backup paths in the same activation set MUST not share the bandwidth!

12. Jan 29, 2006Lahore University of Management Sciences12 Outline Background Forwarding and Routing in IP and MPLS Networks Network Service Requirements Protection Routing in MPLS Terminology: Types of Backup Paths Backup Bandwidth Sharing Activation sets Failures and Backup Path Activation Distinguishable Failure Events: Ideal Case Actual Failures Control Plane Mechanism Outline of Proof

13. Jan 29, 2006Lahore University of Management Sciences13 Distinguishable Failure Events Primary Path Backup Path Focus on link (I,J) and Node J and recall: A I J K PLR: Point of Local Repair nnhop: p1 nhop: p2 Point of local repair (PLR) somehow knows the type of failure!  nhop protects link only i.e., (I,J)  nnhop protects link (I,J) and node J If node I finds that link (I,J) has failed: p1 and p2 are activated If node I finds that node J has failed: ONLY p1 is activated p2 may share bandwidth with other nnhops that protect node j L p3

14. Jan 29, 2006Lahore University of Management Sciences14 Actual Failures Consider the failure of link (I,J) Both p1 and p2 need to be activated, anyways! Knowing that this is a link failure will not save anything Consider the failure of node J Only p1 needs to be activated (if failure type is known!) What if node I doesn’t know the type of failure? Two options: Wait to “discover” if it was a link or node failure High recovery latency (BAD!) Activate both p1 and p2 instantaneously Now p2 will not be able to share with p3 (BAD!)

15. Jan 29, 2006Lahore University of Management Sciences15 Control Plane Mechanism Routing strategy Do not oversubscribe Use sharing as if adjacent nodes can distinguish the node failures from the link failures That is, provide sharing between p2 and p3 In reality PLRs will not be able to disambiguate link/node failures Activate p1 and p2 (assuming link fail situation – worst case!) If link had failed: p1 and p2 really needed to be activated – we are okay! If node had failed: p2 (nhop) has been activated by mistake You may notice reservation violation at some nodes (where the backup paths p2 and p3 were sharing) Abort all nhop paths that are violating the reservations

16. Jan 29, 2006Lahore University of Management Sciences16 Outline of Proof Define: G uv : Bandwidth reserved on link (u, v) for all backup LSPs I uv : Actual backup bandwidth that falls on link (u, v), after the occurrence of a failure A reservation violation happens if I uv > G uv No oversubscription – sharing between p2 and p3: Guv = max(bw(p1)+bw(p2), bw(p1)+bw(p3)) – worst case When failure occurs, activate p1 and p2 If it was link (I, J) that had failed, we are okay If it was node J that had failed, p3 also gets activated Worst case Iuv would have been bw(p1)+bw(p2)+bw(p3) Our control plane mechanism ensures Iuv ≤ bw(p1)+bw(p3) This implies that Guv ≥ Iuv in the worst case

17. Jan 29, 2006Lahore University of Management Sciences17 Questions & Answers