Services; Maintenance Points; Mip Creation - Cisco NCS 5500 Series Configuration Manual

Ethernet CFM

Services

A CFM service allows an organization to partition its CFM maintenance domain, according to the connectivity
within the network. For example, if the network is divided into a number of virtual LANs (VLANs), a CFM
service is created for each of these. CFM can then operate independently in each service. It is important that
the CFM services match the network topology, so that CFM frames relating to one service cannot be received
in a different service. For example, a service provider may use a separate CFM service for each of their
customers, to verify and manage connectivity between that customer's end points.
A CFM service is always associated with the maintenance domain that it operates within, and therefore with
that domain's maintenance level. All CFM frames relating to the service carry the maintenance level of the
corresponding domain.
CFM Services are referred to as Maintenance Associations in IEEE 802.1ag and as Maintenance Entity
Note
Groups in ITU-T Y.1731.

Maintenance Points

A CFM Maintenance Point (MP) is an instance of a particular CFM service on a specific interface. CFM only
operates on an interface if there is a CFM maintenance point on the interface; otherwise, CFM frames are
forwarded transparently through the interface.
A maintenance point is always associated with a particular CFM service, and therefore with a particular
maintenance domain at a particular level. Maintenance points generally only process CFM frames at the same
level as their associated maintenance domain. Frames at a higher maintenance level are always forwarded
transparently, while frames at a lower maintenance level are normally dropped. This helps enforce the
maintenance domain hierarchy described in the
CFM frames for a particular domain cannot leak out beyond the boundary of the domain.
There are two types of MP:
• Maintenance End Points (MEPs)—Created at the edge of the domain. Maintenance end points (MEPs)
are members of a particular service within a domain and are responsible for sourcing and sinking CFM
frames. They periodically transmit continuity check messages and receive similar messages from other
MEPs within their domain. They also transmit traceroute and loopback messages at the request of the
administrator. MEPs are responsible for confining CFM messages within the domain.
• Maintenance Intermediate Points (MIPs)—Created in the middle of the domain. Unlike MEPS, MIPs
do allow CFM frames at their own level to be forwarded.

MIP Creation

Unlike MEPs, MIPs are not explicitly configured on each interface. MIPs are created automatically according
to the algorithm specified in the CFM 802.1ag standard. The algorithm, in brief, operates as follows for each
interface:
• The bridge-domain or cross-connect for the interface is found, and all services associated with that
bridge-domain or cross-connect are considered for MIP auto-creation.
Interface and Hardware Component Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release
6.1.x
28
"Maintenance Domains" section on page
Configuring Ethernet OAM
69, and ensures that