Troubleshooting Guide

Fault isolation
Fault isolation is achieved through the use of Linktrace Messages (LTM). LTM is intercepted by all
the MPs on the way to the destination MP. Avaya Virtual Services Platform 8000 Series supports
two types of LTM.
The first type, the unicast LTM, can be addressed to either MEP or MIP MAC address. Each MP on
the way decrements the TTL field in the LTM frame, sends Linktrace Reply (LTR), and forwards the
original LTM to the destination. The LTM is forwarded until it reaches its destination or the TTL value
is decremented to zero. LTR is a unicast message addressed to the originating MEP.
The second type, the proprietary LTM, is used to map the MAC addresses of the SPBM network; in
this case the target MAC is not an MP, but rather a service instance identifier (I-SID).
Link trace message
Connectivity Fault Management offers link trace messaging for fast fault detection. Link trace
messages allow operators, service providers and customers to verify the connectivity that they
provide or use and to debug systems.
Link trace message — unicast
The link trace message (LTM) is often compared to traceroute. A MEP transmits the LTM packet.
This packet specifies the target MAC address of an MP which is the SPBM system id or the virtual
SMLT MAC. MPs on the path to the target address respond with an LTR.
• Trace the path to any given MAC address.
• DA is unicast
• LTM contains:
- Time to live (TTL)
- Transaction Identifier
- Originator MAC address
- Target MAC address
• CFM unaware entities forward the frame as is like any other data frame.
• MIP or MEP that is not on the path to the target discards the LTM and does not reply.
• MIP that is on the path to the target
- Forwards the LTM after decrementing the TTL and replacing the SA with its own address.
- Sends a reply (LTR) to the originator.
- Identifies itself in the forwarded LTM and LTR by modifying TLV information.
• If the MIP or MEP is a target
- Sends an LTR to the originator.
- Identifies itself in the forwarded LTM and LTR by modifying TLV information.
CFM fundamentals
January 2017 Troubleshooting 149
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