IEEE 802.1ag is a standard define by IEEE for OAM (Operation, Administration and Maintenance).
It is an end-to-end protocol for proactive connectivity monitoring and fault verification.
CC’s detects link/fabric failure through periodic exchange of messages
Loopback identifies the precise location of the fault
LinkTrace can trace the path across the network
Ping every port in the network
EthOAM can be used as a basis for providing additional functionalites (Y.1731),
Performance measurement (loss, delay)
Diagnostics – AIS, EHT-LCK
MEPs and MIPs. (Maintenance End/Intermediate Points)
MEPs initiate OAM commands. MEPs prevent leaking between domains.Thus MEPs are the end points in a Domain.
MIPs passively receive and respond to OAM frames.
Maintenance Association (MA) is a logical connection between 2 or more MEPs.
Maintenance Domain: One or more MAs under the same administrative control.
Levels: There are 8 levels defined in 802.1ag
Continuity Check Message
Every MEP in a Maintenance Domain multicasts Connectivity Check (CC) messages periodically (say once per second).
All MIPs and MEPs in that domain will receive it but will not act on it.
MEPs and MIPs will build a MEP database. [MEP DA, Port ..]
MEPs receiving this CC message will catalog it, and know that the maintenance association (MA) between itself and the MEP sending the CC is functional, including all intermediate MIPs
Link trace Message
Link trace Message is used by one MEP to trace the path to another MEP in the same domain. It is needed for Loopback.
All intermediate MIPs respond back with Link trace reply to the originating MEP.
MIPs forward the Linktrace message till the edge of the domain.
Link trace always returns the same path unless there is a STP reconfiguration due to fault.
Loop Back Message
Loopback message helps the MEP identify the precise fault location along a ME.
Loopback message is issued by a MEP to a given MIP along a MA.
Appropriate MIP will respond back with a Loopback Reply.
The MIP at the other end of the fault will not respond.
How do you know the MAC address of the MIP to Loopback? By using a Link Trace.