D-Link DGS-3700-12 User Manual page 269

OAM
CFM
Ethernet OAM
DULD Settings
Cable Diagnostics
CFM
Connectivity Fault Management (CFM) is defined by IEEE 802.1ag, which is a standard for detecting, isolating and
reporting connectivity faults in a network. CFM is an end-to-end per-service-instance Ethernet layer operation,
administration, and management (OAM) function. CFM functions include path discovery, fault detection and fault
verification and isolation as defined by 802.1ag.
Ethernet CFM frames have a special Ether Type (0x8902). All CFM messages are confined to a maintenance domain
per VLAN basis. There are different message types which are identified by unique Opcode of the CFM frame payload.
CFM message types that are supported include; Continuity Check Message (CCM), Loopback Message and
Response (LBM, LBR) and Linktrace Message and Response (LTM and LTR).
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 reffering 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.
DGS-3700-12/DGS-3700-12G Series Layer 2 Gigabit Ethernet User Manual
Section 10
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