Web Management Guide-R04

Chapter 13 | Basic Administration Protocols
Connectivity Fault Management
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two operator domains which include access points marked “O
1
” and “O
2
”
respectively. The users of these domains can see their respective MEPs as well as all
the MIPs within their domains. There is a service provider domain at the second
level in the hierarchy. From the service provider’s view, the access points marked
“P” are visible, and all access points within the operator domains have also been
made visible as MIPs according to common practice. And finally, there is a customer
domain at the top of the hierarchy. Users at this level can only see the access points
marked “C” on the outer domain boundary. Again, normal practice is to hide the
internal structure of the network from outsiders to reduce security risks.
Figure 337: Multiple CFM Maintenance Domains
Note that the Service Instances within each domain shown above are based on a
unique maintenance association for the specific users, distinguished by the domain
name, maintenance level, maintenance association’s name, and assigned VLAN.
Basic CFM Operations
CFM uses standard Ethernet frames for sending protocol messages. Both the source
and destination address for these messages are based on unicast or multicast MAC
addresses, and therefore confined to a single Layer 2 CFM service VLAN. For this
reason, the transmission, forwarding, and processing of CFM frames is performed
by bridges, not routers. Bridges that do not recognize CFM messages forward them
as normal data. There are three basic types of CFM messages, including continuity
check, link trace, and loop back.
Continuity check messages (CCMs) are multicast within a single Service Instance
(i.e., a specific MA), allowing MEPs to discover other MEPs within the same MA, and
MIPs to discover MEPs. Connectivity faults are indicated when a known MEP stops
sending CCMs, or a remote MEP configured in a static list does not come up.
Configuration errors, such as a cross-connect between different MAs, are indicated
when a CCM is received with an incorrect MA identifier or maintenance level.
Loopback messages are used for fault verification. These messages can be sent
using the MAC address of any destination MEP within the same MA. If the target
MEP’s identifier has been discovered through CCM messages, then a loop back
Customer MA
Provider MA
Operator 1 MA Operator 2 MA
C
C
C
C
O
1
O
1
P
O
2
O
2
P
P
O
1
O
2
P