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Chapter 8 Ethernet OAM
OAM Overview
Ethernet OAM (Operation, Administration, and Maintenance) is a Layer 2 protocol for monitoring
and troubleshooting Ethernet networks. It can report the network status to network administrators
through the OAMPDUs exchanged between two OAM entities, facilitating network management.
Ethernet OAM is a slow protocol with very limited bandwidth requirement. The frame transmission
rate is limited to a maximum of 10 frames per second; therefore, the impact of OAM on data traffic
is negligible.
On a point-to-point link between two OAM-enabled devices, OAM helps to monitor the link status
from the following three points.
1. Link performance monitoring, for detecting link errors.
2. Fault detection and alarm, for reporting link errors to the administrators.
3. Loopback testing, for detecting link errors through non-OAMPDUs.
Currently, Ethernet OAM is mainly used to monitor the data link in the “last mile”.
OAMPDUs
There are six types of OAMPDUs. The following figure shows the details of the most commonly
used OAMPDUs, namely, Information OAMPDU, Event Notification OAMPDU and Loopback
Control OAMPDU.
Figure 8-1 OAMPDUs
As Figure 8-1 shows, OAMPDUs are standard length Ethern
et frames. They must be untagged
and range from 64 to 1518 bytes.
(1) Dest addr: The Dest addr (Destination MAC address) of an OAMPDU is the
Slow_Protocols_Multicast address (01:80:c2:00:00:02).
(2) Source addr: The Source addr is the MAC address associated with the port through which
the OAMPDU is transmitted.
(3) Type: The type field is fixed to 0x8809.
(4) Sub-type: The Sub-type field is fixed to 0x03.
(5) Flags: The flags field contains status bits of an OAM entity.
(6) Code: The code field identifies the specific type of OAMPDU. As mentioned above,
Information OAMPDU, Event Notification OAMPDU and Loopback control OAMPDU are
commonly used, and their codes are 0x00, 0x01, and 0x04. The three OAMPDUs are
described as follows.
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