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.
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.
A MEP that is not the target but is on the path to the target
Generates a reply as described above.
It also sets one of the flags fields in the reply to indicate that it is the terminal MEP.
The multicast link trace message (LTM) can be used to trace the multicast tree from any node on any I- SID using the nickname MAC address and the I-SID multicast address.
Specifying a multicast target address for an LTM allows for the tracing of the multicast tree corresponding to that destination address (DA). With a multicast target every node that is in the active topology for that multicast address responds with a Linktrace reply and also forwards the LTM frame along the multicast path. Missing Linktrace replies (LTRs) from the nodes in the path indicate the point of first failure.
This functionality allows you to better troubleshoot I-SID multicast paths in a SPBM network.