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802.3ah | 95
Link Layer OAM Operational Modes
When participating in EFM OAM, system may operate in active or passive mode.
• Active mode—Active mode systems initiate discovery. Once the Discovery process completes, they
can send any OAMPDU while connected to a peer in Active mode, and a subset of OAMPDUs if the
peer is in Passive mode (see Table 6-1).
• Passive mode—Passive mode systems wait for an active mode system to initiate discovery, and do not
send Variable Request or Loopback Control OAMPDUs.
Taken from IEEE 802.3ah, Table 6-1 summarizes the permitted actions in each role.
Link Layer OAM Discovery
OAM Discovery is the mechanism a Link Layer OAM-capable system uses to determine if the remote
system on the link has OAM functionality enabled. OAM Discovery ascertains OAM parameters, such as
maximum allowable OAMPDU size, and supported functions such as OAM remote loopback.
The discovery process is as follows:
1. If the link is not in Fault state, Active mode systems send Information OAMPDUs that contain (only)
the Local Information TLV.
2. Once a system receives an Information OAMPDU, it responds with an Information OAMPDU that
contains the Local and Remote Information TLV. Negotiation is complete when both systems have
received their peer’s information and are satisfied with it; to be satisfied, both peers on the link must be
have link performance event monitoring enabled.
3. When negotiation is complete, both peers may send any type of OAMPDU.
Table 6-1. Active Mode and Passive Mode Behaviors
Capability Active Passive
Initiates OAM Discovery process Yes No
Reacts to OAM Discovery process initiation Yes Yes
Required to send Information OAMPDUs Yes Yes
Permitted to send Event Notification OAMPDUs Yes Yes
Permitted to send Variable Request OAMPDUs Yes No
Permitted to send Variable Response OAMPDUs (the peer must be in Active mode) Yes Yes
Permitted to send Loopback Control OAMPDUs Yes No
Reacts to Loopback Control OAMPDUs (the peer must be in Active mode) Yes Yes
Permitted to send Organization Specific OAMPDUs Yes Yes