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xStack® DES-3200 Series Layer 2 Ethernet Managed Switch CLI Reference Guide
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CONNECTIVITY FAULT MANAGEMENT COMMANDS
Connectivity Fault Management (CFM) or Ethernet Connectivity Fault Management is an end-to-end Ethernet layer OAM
protocol. CFM is defined by IEEE 802.1ag and includes connectivity monitoring, fault notification and means of isolating faults
on large Ethernet metropolitan-area networks (MANs) and WANs.
Ethernet has traditionally operated on isolated enterprise LANs. As Ethernet has been expanded to operate on the much larger
scale carrier networks that encompass multiple administrative domains, the demands of the much larger and more complex
networks required a new set of OAM capabilities. Since these larger scale networks have a very large user base, carry more
diversified network applications and typically span a much larger geographical area than traditional enterprise Ethernet LANs
where link uptime is crucial, a means of dealing with connectivity faults able to operate in Ethernet became necessary. Since none
of the existing OAM protocols could adequately address this new circumstance, Ethernet Connectivity Fault Management has
been developed in order to meet the new operational management needs created by the application of Ethernet technologies to
MANs and WANs.
Ethernet CFM provides Ethernet network service providers with various benefits such as end-to-end service-level OAM and lower
operating expenses, all operated on top of a familiar Ethernet platform.
CFM introduces some new terms and concepts to Ethernet, these are briefly described below.
Maintenance Domain
A maintenance domain is generic term referring to a management area created for the purpose of managing and administering a
network. A maintenance domain is operated by a single entity or “owner” and defined by a boundry with a set of ports internal to
this boundry.
An Ethernet CFM maintenance domain, referred to in this manual simply as an MD, exists in a hierarchical relationship to other
MDs. Typically a large MAN or WAN can be partitioned into a higherarchy based on the size of domain that mirrors the
structural relationship of customers, service providers and operators. The service providers have end-to-end service responsibility
while operators provide service transport across subnetworks. The hierarchy is defined by a maintenance level value ranging from
0 to 7 where 7 is the highest level and 0 the lowest level. The larger the MD is, the higher its maintenance level will be. For
example, if the customer domain is the largest MD, it should be assigned a maintenance level of 7, the operator MD being the
smallest, receives a maintenance level of 0 with the service provider domain being in between these values. Maintenance levels
are manually assigned by the network admisitrator. All levels of the MD hierarchy must operate together.
Nesting of MDs is allowed, however they cannot intersect since this violates the requirement that management of MDs be done by
a single owner. If two or more domains are nested, the outer domain must be assigned a higher maintenance level than the nested
domains.
CFM operations and message exchanges are conducted on a per-domain basis. This means for example, that CFM operating at
level 3 does not allow discovery of the level 3 network by higher levels.
Maintenance Association
A maintenance association (MA) in CFM is a set of MEPs that have been configured with the same management domain level and
maintenance association identifier (MAID).
Different MAs in an MD must have different MA Names. Different MAs in different MDs may have the same MA Name. The
MEP list specified for a MA can be located in different devices. MEPs must be created on ports of these devices explicitly. A
MEP will transmit CCM packets periodically across the MA. The receiving MEP will verify these received CCM packets from
other MEPs against this MEP list for configuration integrity check.
Maintenance Point
A maintenance point in CFM is a point of demarcation on a port within a maintenance domain. Maintenance points filter CFM
frames within the boundries of an MD by dropping frames that do not belong to the correct maintenance level. There are two
types of maintenance points, Maintenance Endpoints (MEPs) and Maintenance Intermediate Points (MIPs). MEPS and MIP
are manually configured by a network administrator.
A MEP exists at the edge of a maintenance domain, defining the boundry of the MD. MEP functions include filtering CFM
messages so that they are confined to the MD. A MEP can be configured to transmit Connectivity Check Messgaes (CCMs) and
will transmit treacroute and loopback messages if configured to do so. A MEP can be Inward facing or Outward facing.
An Inward facing MEP source CFM frames toward the bridge relay function, not through the bridge port on which the MEP is
configured. An Inward facing MEP drops all CFM frames at its level or lower that are received from the Inward side; and
forwards all CFM frames at a higher level regardless of the origin of the frame, Inward or Outward. If the port on which the
inward MEP is configured is blocked by Spanning-Tree Protocol, the MEP can no longer transmit or receive CFM messages.
An Outward facing MEP source frames toward the bridge port and can only be configured on routed ports. An Outward facing
port drops all CFM frames at it level or lower coming from the bridge relay function side. It processes all CFM frames at its level,
and drops all CFM frames at a lower level, coming from the bridge port. An Outward facing port forwards all CFM frames at