© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 1

MPLS –TP Fault OAM

draft-ietf-mpls-tp-fault-01

George Swallowswallow@cisco.comIETF77 March 2010

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 2

Why MPLS-TP OAM?

GoalsSupport the requirements of transport

Build better OAM for MPLS

Be compatible with deployed MPLS equipment

There is existing MPLS equipment that cannot run BFD at 3.3, 10 or even 50 ms at scale

There is a desire among owners of that equipment for faster failover

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 3

Hold off Timer?

In Sonet equipment AIS is sent continuously

Lack of an LDI signal is handled with a hold-off timer which allow time for the server layer to recover before the client layer reacts

This prevents unnecessary protection switches

In MPLS-TP AIS is sent at a max rate of 1 per sec and does not time out for 3.5 seconds

There appears to be no reasonable and useful timer setting for a hold-off timer!

This is the motivation for the Link Down Indication

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 4

Link Down Indication (LDI)

LDI carries all the same semantics as AIS plus the indication of a hard failure

In fact it would be fine to have just an AIS message and a flag for LDI

Flag clear = Protecting State; Flag set = Unavailable State

LDI is only need when CC is running slowlyIf CC is running fast (detect time ~500 ms or less) then LDI is treated just like AIS

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 5

Link Down Indication (LDI)

The decision to send AIS or LDI is driven from the APS state

LDI must be sent whenever the server layer enters the unavailable state

When LDI is received by an MPLS-TP LSP’s MEP it is used to

Suppresses alarms due to any CC failure – just like AIS

If the LSP is protected and CC is running slowly, and if no CC failure has occurred (i.e. BFD is up), may trigger path protection

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AIS / LDI Fault Generation

Client LSP

Server Working LSP

Server Protection LSP

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Case 1: An unprotected link

Server Path is unprotected

Control function sets Server MEP W to send LDI on CC failure

Server Path WServer Path WServer MEP WServer MEP W

Client PathClient Path

Server APS/Control

Server APS/Control

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Case 2: Both Working and Protection are Up

CC functions are reporting that both W and P are up

APS is in the Normal State

Control Function sets both MEPs to send AIS on CC failure

Server LSP PServer LSP P

Server LSP WServer LSP W

Server MEP PServer MEP P

Server MEP WServer MEP W

Client PathClient Path

Server APS/Control

Server APS/Control

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Case 3: Protection Up, Working Fails

Server LSP W fails, Server MEP W begins sending AIS

Server LSP PServer LSP P

Server LSP WServer LSP W

Server MEP PServer MEP P

Server MEP WServer MEP W

Client LSPClient LSP

X

Server APS/Control

Server APS/Control

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 10

Case 3: Protection Up, Working Fails

Server LSP W fails, Server MEP W begins sending AIS

APS / Control Function moves selector to Protection LSP

AIS ceases to be inserted in Client LSP

APS enters Protecting State, Control Function sets Server MEP P to send LDI

Server LSP PServer LSP P

Server LSP WServer LSP W

Server MEP PServer MEP P

Server MEP WServer MEP W

Client LSPClient LSP

X

Server APS/Control

Server APS/Control

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 11

Case 4: Working has failed; Protection Fails

Server LSP P fails, Server MEP P begins sending LDI

APS enters Unavailable State

Server LSP PServer LSP P

Server LSP WServer LSP W

Server MEP PServer MEP P

Server MEP WServer MEP W

Client LSPClient LSP

X

Server APS/Control

Server APS/ControlX

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Case 5: Protection Up; Working comes Up

Server MEP W CC fault clears

APS enters Normal State

APS / Control Function sets Server MEP P to send AIS

Server LSP PServer LSP P

Server LSP WServer LSP W

Server MEP PServer MEP P

Server MEP WServer MEP W

Server APS/Control

Server APS/Control

Client LSPClient LSP

X

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 13

Default sending behavior

OpCode set to AIS, LDI or LKR

R-flag set to zero (not used)

Refresh Timer default value is 1 sec

Message continuously transmitted until condition clears

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 14

For existing MPLS equipment, receiving control packets can be taxing, particularly if many LSP terminating at a node are receiving fault messages

Solution is to allow back-off after transmitting 3 times at one second

Optional Sending Behavior

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 15

OpCode set to AIS, LDI or LKR

R-flag set to zero

Refresh Timer set to configured value (default 20 sec)

Message transmitted three times at one second intervals

Message continuously transmitted according to refresh timer until condition clears

Optional Sending Behavior

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Used when refresh timer is set long

When fault / lock condition clearsSet R-bit to one

Transmit three times at refresh interval of 1 sec

Optional Clearing Behavior

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Next Steps

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