Juniper JUNOSE 11.1.X - LINK LAYER CONFIGURATION 4-7-2010, Configuration Manual

Page: 267 / 774

The discovery mode that you set up for an OAM entity also determines certain other
attributes that can be initiated by an OAM entity. For example, a passive mode OAM
entity cannot initiate a variable request or a loopback procedure. In a carrier
environment, the customer edge (CE) devices are normally configured for passive
mode operation, whereas the provider edge (PE) equipment is configured for active
mode operation.
Information OAM PDU Components
An OAM entity in active mode initiates the discovery process by sending an
Information OAM PDU to the slow protocols multicast address (destination MAC
address of the remote entity) at a configured rate. The transmitted Information OAM
PDU contains a local-information type-length-value (TLV). This TLV contains the
following fields:
■
State—Transmission or receiving state for forwarded packets. The mode can be
either active or passive and can be used to determine device functionality.
■
Capabilities of the OAM sublayer—Advertises the capabilities of the local OAM
entity. With this information a peer can determine what functions are supported
and accessible, such as loopback or unidirectional operation. This field also
specifies the maximum OAM PDU size for receipt and delivery. This information,
together with the rate limiting value of 10 frames per second, can be used to
specify the bandwidth allocated to OAM traffic.
■
Vendor OUI—Organization unique identifier (OUI), which is controlled by the
IEEE and is typically the first three bytes of a MAC address.
■
Vendor-specific information—A 32-bit identifier, which is used to distinguish the
type of platform in conjunction with the vendor OUI field.
After a local entity sends an Information OAM PDU, the remote OAM entity waits to
receive the local information of the peer. After receipt of the Information OAM PDU,
the OAM entity applies a policy to determine whether an OAM relationship can be
established. For example, loopback mode might be required for the OAM association
to be completed. If the remote entity does not support loopback, the local entity
might disable the OAM association.
Transmission Settings for Information OAM PDUs
After an OAM association is established, Information OAM PDUs are sent at a
configured rate. If no OAM PDUs other than Information OAM PDUs are available
to be sent from the local peer to the remote peer, the local entity sends Information
OAM PDUs that contain both the local and remote information TLVs. This constant
bidirectional transfer of Information OAM PDUs serves as a keepalive mechanism
for the OAM association. If no Information OAM PDUs are received within 5 seconds,
the discovery process restarts and a link-fault event is generated that might cause a
transition in the operational status of the Ethernet interface to the down state. If the
OAM association with the peer is reestablished, OAM clears the link-fault event to
cause a transition of the interface to the operational up state. The operational status
of an interface does not depend only on the OAM status. Other factors, such as the
administrative state of the interface, also impact the operational state.
OAM Discovery Feature
■ 235
Chapter 7: Configuring IEEE 802.3ah OAM Link-Fault Management