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Chapter 20
Checking Status and Connectivity
Table 20-3
Functions
Initiate CFM messages
Respond to loopback
and link trace messages
Catalog
continuity-check
information received
Forward CFM messages No
Maintenance endpoints reside at the edge of a maintenance domain, while maintenance intermediate
points are internal to the domain. An intermediate point will forward CFM packets (unless it is a
loopback or link trace destined for that intermediate point), while endpoints do not forward CFM packets
because they must keep them within the domain. The only exception is when an endpoint is also acting
as an intermediate point for a higher-level domain, in which case, it will forward the CFM packets as
long as they are part of the higher-level domain.
Figure 20-3 shows an example where a service provider is using the networks of two operators to provide
service. The service provider maintenance level is shown in blue. The maintenance levels for Operator
A and Operator B are shown in orange and violet, respectively. Two special-case maintenance levels are
the customer level (shown in green) and the physical layer level (shown in black). The customer level
allows the customer to test connectivity (using connectivity checks) and isolate issues (using loopback
and link trace). The physical layer level defines the narrowest possible maintenance domain, which is a
single link domain.
The designation of maintenance points as maintenance endpoints or maintenance intermediate points for
the Operator A (or the Operator B) level is relative to that level only. When these maintenance points are
observed relative to the service provider level, maintenance endpoints at the Operator A level translate
into either maintenance endpoints or maintenance intermediate points at the service provider level.
Maintenance intermediate points at the Operator A level translate into transparent points at the service
provider level. Also, the demarcation of maintenance points as maintenance endpoints or maintenance
intermediate points within a domain is left to the discretion of the administrator, because these points
indicate points of particular relevance for the management of the network.
Figure 20-3 shows an example of how the CFM messages are used across the domains. The customer
could use a CFM loopback or link trace to isolate a fault between the maintenance point M, which is on
the Customer Premises Equipment (CPE), and the intermediate point L, which is on the user-facing
provider edge equipment (U-PE). The link between the CPE and U-PE is a single hop. The customer
would know which link has the fault. However, if the fault is between the two intermediate points (the
Ls), the customer will need to rely on the service provider to determine between which maintenance (M)
or intermediate (L) points that the fault has occurred. The service provider may simply isolate the fault
to a specific operator's network and will rely on the operator to isolate the fault to a specific link in its
network.
Each different organization (customer, service provider, and operator) can isolate the fault within the
organization's maintenance level, without the service provider having to share its network information
to the customer, or the operator having to share its network information to the service provider
OL-8978-04
Maintenance Point Classifications
Maintenance Endpoint
Yes
Yes
Yes
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
Configuring Metro Ethernet Connectivity Fault Management
Maintenance
Intermediate Point
No
Yes
Yes
Yes
Transparent Point
No
No
No
Yes
20-41
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