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xStack® DES-3200 Series Layer 2 Ethernet Managed Switch CLI Reference Guide
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higher levels regardless of which direction the frames come in. If the port on which the outward MEP is configured is blocked by
Spanning-Tree Protocol, the MEP can still transmit and receive CFM messages through the bridge port.
A MIP is a maintenance point that is internal to an MD, not at the boundry. A MIP receives CFM frames from other MIPs and
from MEPs. These frames are cataloged and forwarded using the bridge relay function and bridge port. All CFM frames at a lower
level than the MIP are blocked and dropped regardless of the origin. All CFM frames at a higher level are forwarded regardless of
the origin. If the port on which a MIP is configured is blocked by Spanning-Tree Protocol, the MIP cannot receive CFM messages
or relay them toward the bridge relay function side. The MIP can, however, receive and respond to CFM messages from the
bridge port.
CFM messages include Continuity Check Messages (CCMs), Loopback Messages (LBMs) and Link Trace Messages (LTMs).
CFM uses standard Ethernet frames that can be sourced, terminated, processed and relayed by bridges. Routers support limited
CFM functions.
Continuity Check Messages (CCMs) are multicast messages exchanged among MEPs. CCMs allow discovery of MEPs for
other MEPs within a domain and allow MIPs to discover MEPs. CCMs are confined to a maintenance domain. CCMs are
cataloged by MIPs are the same maintenance level and terminated by remote MEPs at the same maintenance level. They are
unidirectional (no response soliticitation) and carry the status of the port on which the MEP is configured. LBMs are similar to
Ping or ICMP messages in that they indicate only whether a destination is reachable and do not allow discovery of each hop.
Link Trace Messages (LTMs) are multcast CFM frames sent by MEPs to identify adjacency relationships with remote MEPs and
MIPs at the same maintenance level. The message body of an LTM includes a destination MAC address of a target MEP that
terminates the linktrace. When a MIP or MEP receives an LTM, it generates a unicast Link Trace Reply (LTR) to the initiating
MEP. It also forwards the LTM to the target MEP destination MAC address. An LTM effectively traces the path to the target
MEP or MIP.
Loopback Messages (LBMs) are similar to Ping or ICMP messages in that they indicate only whether a destination is reachable
and do not allow the discovery of each hop.
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Figure 3 - 1. OAM Domain Architecture
Maintenance Association (MA) – Boundaries of an Administrator’s scope of monitoring part of the network
Maintenance Domain (MD) – A level of monitoring within the hierarchy
Maintenance End Points (MEP) – End Points of the MA or MD
Maintenance Intermediate Points (MIP) – Intermediate Points within MA or MD
Note: CE = Customer Equipment