© 2006 Cisco Systems, Inc. All rights reserved. Cisco Confidential Presentation_I D 1 MPLS –TP Fault OAM draft-ietf-mpls-tp- fault-01 George Swallow [email protected] IETF77 March 2010
Mar 27, 2015
© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 1
MPLS –TP Fault OAM
draft-ietf-mpls-tp-fault-01
George [email protected] 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
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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
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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
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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
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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
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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
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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
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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
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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
Address Liaison comments
Incorporate other comments
Republish