Seamless detection of link and node failures for local protection in mpls
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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) Visiting Professor – Chonbuk National University. Outline. Background Forwarding and Routing in IP and MPLS Networks

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Seamless Detection of Link and Node Failures for Local Protection in MPLS

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Seamless detection of link and node failures for local protection in mpls

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)

Visiting Professor – Chonbuk National University

Lahore University of Management Sciences


Outline

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

Lahore University of Management Sciences


Outline1

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

Lahore University of Management Sciences


Forwarding and routing

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)

Lahore University of Management Sciences


Network service requirements

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

Lahore University of Management Sciences


Outline2

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

Lahore University of Management Sciences


Protection in mpls preset backup paths

Protection in MPLS:Preset Backup Paths

Local Protection

Path Protection

S

1

2

3

D

This type of “path Protection” takes 100s of ms.

We need “Local Protection” to quickly switch onto backup paths!

Primary Path

Backup Path

Lahore University of Management Sciences


Nhop and nnhop paths

Primary Path

Backup Path

nhop and nnhop paths

LOCAL PROTECTION (showing one LSP only)

All links and all nodes are protected!

nnhop

A

B

D

C

E

nhop

PLR: Point of Local Repair

 nhop protects link only, e.g., (D,E)

 nnhop protects link (C,D) and node (D)

Lahore University of Management Sciences


Opportunity cost of backup paths

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

Lahore University of Management Sciences


Bw sharing in backup paths

Primary Path

Backup Path

BW Sharing in backup Paths

  • Example:

LSP1

BW: X

Sharing is possible

IF

Links (A,B) and (C,D) do not simultaneously fail!

A

B

X

X

max(X, Y)

X

E

G

F

X+Y

Y

Y

C

D

BW: Y

LSP2

Lahore University of Management Sciences


Activation sets

Activation Sets

Can backup paths always share the bandwidth?

A

A

E

E

B

B

C

C

D

D

Activation set for node B

Activation set for link (A,B)

backup paths in the same activation set MUST not share the bandwidth!

Lahore University of Management Sciences


Outline3

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

Lahore University of Management Sciences


Distinguishable failure events

Primary Path

Backup Path

Distinguishable Failure Events

Point of local repair (PLR) somehow knows the type of failure!

Focus on link (I,J) and Node J and recall:

 nhop protects link only i.e., (I,J)

 nnhop protects link (I,J) and node J

nnhop: p1

A

J

I

K

nhop: p2

PLR: Point of Local Repair

L

p3

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

Lahore University of Management Sciences


Actual failures

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!)

Lahore University of Management Sciences


Control plane mechanism

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

Lahore University of Management Sciences


Outline of proof

Outline of Proof

  • Define:

    • Guv: Bandwidth reserved on link (u, v) for all backup LSPs

    • Iuv: Actual backup bandwidth that falls on link (u, v), after the occurrence of a failure

  • A reservation violation happens if Iuv > Guv

  • 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

Lahore University of Management Sciences


Seamless detection of link and node failures for local protection in mpls

Questions & Answers

Lahore University of Management Sciences


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