1. MPLS-TP Fault Management Draft draft-boutros-mpls-tp-fault-01
MPLS-TP Fault Management Draft draft-boutros-mpls-tp-fault-01.txt Sami Boutros Siva Sivabalan David Ward George Swallow Stewart Bryant

2. Introduction
This draft specifies a fault management mechanism for MPLS-TP LSP.
The proposed mechanism is based on a generic way of notifying a MEP or MIP of a fault on an MPLS-TP LSP using new type of MPLS OAM messages.
A new type of MPLS-OAM Fault Messages (FM) will be sent downstream and upstream from the node that detected the fault.

3. Introduction (cont’d)
Upon receiving an MPLS OAM FM message:
A MIP/MEP activates the backup MPLS-TP LSP (if available) rather than waiting for notification from other fault detection mechanism such as BFD.
A MEP sends MPLS-OAM Connection Verification Message (described in the MPLS-OAM Connection Verification Slides) to verify the new end-to-end path of the MPLS-TP LSP.

4. Problem Definition (example 1)
LSR-1
LSR-2
LSR-3
MPLS-TP LSP
LSR-6
LSR-5
MPLS-TP LSP (backup)
Fault
LSR-4
Consider the above scenario:
There is an MPLS-TP LSP spanning LSR-1, LSR-2, LSR-3, LSR-4 and LSR-5. LSR-1 and LSR-5 act as MEPs and LSR-2 and LSR-3 act as a MIP. Furthermore, the segment between LSR-2 and LSR-3 is protected by another MPLS-TP LSP as shown above.
Assume that there is a fault on segment between LSR-2 and LSR-3, it was detected only by LSR-2.

5. Proposed Solution (example 1)
LSR-1
LSR-2
LSR-3
MPLS-TP LSP
LSR-6
LSR-5
MPLS-TP LSP (backup)
Fault 1 3
LSR-4 1 4 4 2
The proposed solution operates as follows:
Upon detecting failure, LSR-2 activates the backup MPLS-TP LSP that protects the failure, and sends MPLS-OAM FM messages to LSR-1 (upstream) and LSR-6 (downstream via backup MPLS-TP LSP). The MPLS-OAM FM message has an indication that local repair is active on LSR-2.
MPLS-OAM FM message arrives at LSR-6 which simply forwards it to downstream over the backup MPLS-TP LSP.
MPLS-OAM FM message arrives at LSR-3, and since backup MPLS-TP LSP exists on LSR-3, the backup is activated. The MPLS-OAM FM message is forwarded downstream.
Upon receiving MPLS-OAM FM messages, LSR-1 and LSR-5 send MPLS-OAM CV message to verify the new end-to-end path.

6. Problem Definition (example 2)
LSR-1
LSR-2
LSR-3
MPLS-TP LSP
LSR-6
LSR-5
MPLS-TP LSP (backup)
Fault
LSR-4
Consider the above scenario:
This example is similar to the first one except that both LSR-2 and LSR-3 detect the failure.

7. Proposed Solution (example 2)
LSR-1
LSR-2
LSR-3
MPLS-TP LSP
LSR-6
LSR-5
MPLS-TP LSP (backup)
Fault 1 1
LSR-4 3 3 4 1 2 4 1 2
The proposed solution operates as follows:
Upon detecting failure, LSR-2 activates the backup MPLS-TP LSP that protects the failure, and sends MPLS-OAM FM messages to LSR-1 (upstream) and LSR-6 (downstream via backup MPLS-TP LSP). The MPLS-OAM FM message has an indication that local repair is active on LSR-2. Also, since LSR-3 also detects the failure, it also activates the backup MPLS-TP LSP and sends an MPLS-OAM FM message upstream and downstream. The MPLS-OAM FM message has an indication that local repair is active on LSR-3 as well.
MPLS-OAM FM messages arrive at LSR-6 which simply forwards it to upstream and downstream over the backup MPLS-TP LSP.
MPLS-OAM FM message arrives at LSR-3 and LSR-2. Since the failure is already known to LSR-3 and LSR-2, the MPLS-OAM FM message is discarded.
Upon receiving MPLS-OAM FM messages, LSR-1 and LSR-5 send MPLS-OAM CV message to verify the new end-to-end path.

8. Proposed Solution: Fault Removal
MPLS-TP LSP
LSR-1 1 1
LSR-3 2
LSR-4
LSR-5
LSR-2 3 3
LSR-6
MPLS-TP LSP (backup)
Assuming LSR-2 detects fault removal proposed solution operates as follows:
LSR-2 activates the primary MPLS-TP LSP back and sends MPLS-OAM FM messages to LSR-1 (upstream) and LSR-3 (downstream via primary MPLS-TP LSP). The MPLS-OAM FM message has an indication that the specified fault is removed on LSR-2.
MPLS-OAM FM message arrives at LSR-3. Since LSR-3 activates the primary MPLS-TP LSP back, and which forwards the MPLS-OAM FM message downstream to LSR-4 and LSR-5.
Upon receiving MPLS-OAM FM messages, LSR-1 and LSR-5 send MPLS-OAM CV message to verify the new end-to-end path.

9. Proposed Solution: MPLS-OAM Fault Management Message
This MPLS-OAM FM message shall contain:
Source and destination addresses of the two LSRs associated with the fault segment.
Connection ID of the MPLS-TP LSP.
Fault code (this would include link failure, node failure, low memory, high cpu, resource unavailable). A code is required for no fault to notify MIP/MEP when a given fault no longer exists.
An indication whether or not local repair is active.

10. Proposed Solution MPLS OAM Message extensions
The proposed mechanism is based on a set of new TLVs
which can be transported using one of the following
methods:
Using in-band MPLS OAM messages which are forwarded as MPLS packets (non-IP based).
Using LSP-Ping messages where IP/UDP packets are used (IP-based) in compliance with RFC 4379.

11. Proposed Solution new ACH codepoints for in-band option.
| |Version |Flags 0xBB | 0xHH (MPLS-TP Fault) |
MPLS-TP OAM Message Header
The first nibble (0001b) indicates the ACH. The version and the reserved values are both set to 0. MPLS-TP Fault code point = 0xHH. [HH to be assigned by IANA from the PW Associated Channel Type registry.]

12. MPLS-TP Fault Message Format
| Version | Message Type | Operation | Reserved |
| Return Code | Cause Code | Message Length |
| Sender's Handle |
| Message ID |
| TLV's |
~ ~
Message Type Description
0x Downstream Fault
0x Upstream Fault
0x Fault Response
Operation Description
0x Fault added and local repair activated.
0x Fault added with no local repair.
0x Fault removed.