Users Guide

• there are complex interactions between various Layer 2 and Layer 3 protocols such as spanning tree
protocol (STP), link aggregation group (LAG), virtual router redundancy protocol (VRRP), and electronic
commerce messaging protocol (ECMP) configurations.
• ping and traceroute are not designed to verify data connectivity in the network and within each node in
the network (such as in the switching fabric and hardware forwarding tables).
• when networks are built from different operational domains, access controls impose restrictions that
cannot be overcome at the IP level, resulting in poor fault visibility. There is a need for hierarchical
domains that can be monitored and maintained independently by each provider or operator.
• routing protocols choose a subset of the total network topology for forwarding, making it hard to detect
faults in links and nodes that are not included in the active routing topology. This is made more complex
when using some form of traffic engineering (TE) based routing.
• network and element discovery and cataloging is not clearly defined using IP troubleshooting tools.
There is a need for Layer 2 equivalents to manage and troubleshoot native Layer 2 Ethernet networks. With
these tools, you can identify, isolate, and repair faults quickly and easily, which reduces operational cost of
running the network. OAM also increases availability and reduces mean time to recovery, which allows for
tighter service level agreements, resulting in increased revenue for the service provider.
In addition to providing end-to-end OAM in native Layer 2 Ethernet Service Provider/Metro networks, you can
also use CFM to manage and troubleshoot any Layer 2 network including enterprise, datacenter, and cluster
networks.
Maintenance Domains
Connectivity fault management (CFM) divides a network into hierarchical maintenance domains, as shown in
the following illustration.
A CFM maintenance domain is a management space on a network that a single management entity owns and
operates. The network administrator assigns a unique maintenance level (from 0 to 7) to each domain to
define the hierarchical relationship between domains. Domains can touch or nest but cannot overlap or
intersect as that would require management by multiple entities.
Figure 3. Maintenance Domains
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