Understanding How Metro Ethernet Connectivity Fault Management Works; Connectivity Fault Management Protocols; Maintenance Domains - Cisco WS-C6506 Software Manual

Chapter 20 Checking Status and Connectivity

Understanding How Metro Ethernet Connectivity Fault Management Works

Metro Ethernet connects multiple customer sites to form one virtual private network (VPN). A Metro
Ethernet network consists of networks from multiple operators that are supported by one service
provider. Networks provided and managed by multiple independent service providers have restricted
access to each other's equipment. Because of the diversity in these multiple-operator networks, failures
must be isolated quickly. As a Layer 2 network, Ethernet must be capable of reporting network faults at
Layer 2. IEEE 802.3ah is a point-to-point and per physical wire OAM protocol; it is not a service-aware
switch protocol. IEEE 802.1ag CFM is a service level OAM protocol that provides tools for detecting
and isolating connectivity failures in the network.

Connectivity Fault Management Protocols

IEEE 802.1ag draft 8.0 Metro Ethernet CFM incorporates several OAM facilities that allow you to
manage Metro Ethernet networks, including an Ethernet continuity check, an end-to-end Ethernet
traceroute, a Link Trace Message (LTM), a Loopback Message (LBM), and a Loopback Reply (LBR).
These Metro Ethernet CFM elements allow you to quickly identify problems in your network.
The following three protocols work together to help you debug Ethernet networks:
•
•
•

Maintenance Domains

Ethernet CFM, within any given service provider network, consists of hierarchical maintenance
domains. A maintenance domain is an administrative domain for the purpose of managing and
administering a network. A domain is assigned a unique maintenance level (among eight possible levels)
by the administrator, which is useful for defining the hierarchical relationship of domains. Maintenance
domains may nest or touch but cannot intersect. If the two domains nest, the outer domain must have a
higher maintenance level that is contained within it. A maintenance domain is defined by determining
which bridge ports are interior to the domain. See Figure 20-2 for an example of a maintenance domain.
OL-8978-04
Continuity Check—These heartbeat messages are issued periodically by the maintenance endpoints.
They allow maintenance endpoints to detect a loss of service connectivity among themselves. They
also allow maintenance endpoints to discover other maintenance endpoints within a domain and
allow maintenance intermediate points to discover maintenance endpoints.
Link Trace—These messages are transmitted by a maintenance endpoint by the request of the
administrator to track the path (hop-by-hop) discovery to a destination maintenance endpoint. They
allow the transmitting node to discover connectivity data about the path. Link trace messages are
nonguaranteed datagram delivery packets that are transmitted similarly to User Datagram Protocol
(UDP) traceroute messages.
Loopback—These messages are transmitted by a maintenance endpoint by the request of the
administrator to verify connectivity to a particular maintenance point. Loopback indicates whether
the destination is reachable or not; it does not allow hop-by-hop discovery of the path. Loopback
messages are similar to ICMP echoes (ping).
Configuring Metro Ethernet Connectivity Fault Management
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
20-39