Cisco Catalyst 4500 Series, Software Configuration Manual

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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 75 Configuring Ethernet OAM and CFM
About Ethernet CFM
Maintenance Associations and Maintenance Points
A maintenance association (MA) identifies a service that can be uniquely identified within the
maintenance domain. The CFM protocol runs within a maintenance association.A maintenance point is
a demarcation point on an interface that participates in CFM within a maintenance domain. Maintenance
points drop all lower-level frames and forward all higher-level frames. There are two types of
maintenance points:
•
Maintenance end points (MEPs) are points at the edge of the domain that define the boundaries and
confine CFM messages within these boundaries. Outward facing or Down MEPs communicate
through the wire side (connected to the port). Inward facing or Up MEPs communicate through the
relay function side, not the wire side.
Note
CFM draft 1 referred to inward and outward-facing MEPs. CFM draft 8.1 refers to up and down
MEPs, respectively. This document uses the CFM 8.1 terminology for direction.
CFM draft 1 supported only up MEPs on a per-port or per-VLAN basis. CFM 802.1ag supports up
and down per-VLAN MEPs, as well as port MEPs, which are untagged down MEPs that are not
associated with a VLAN. Port MEPs are configured to protect a single hop and used to monitor link
state through CFM. If a port MEP is not receiving continuity check messages from its peer (static
remote MEP), for a specified interval, the port is put into an operational down state in which only
CFM and OAM packets pass through, and all other data and control packets are dropped.
– An up MEP sends and receives CFM frames through the relay function. It drops all CFM frames
at its level or lower that come from the wire side, except traffic going to the down MEP. For
CFM frames from the relay side, it processes the frames at its level and drops frames at a lower
level. The MEP transparently forwards all CFM frames at a higher level, regardless of whether
they are received from the relay or wire side. If the port on which MEP is configured is blocked
by STP, the MEP can still send or receive CFM messages through the relay function. CFM runs
at the provider maintenance level (UPE-to-UPE), specifically with up MEPs at the user network
interface (UNI).
–
A down MEP sends and receives CFM frames through the wire connected to the port on which
the MEP is configured. It drops all CFM frames at its level or lower that come from the relay
side. For CFM frames from the wire side, it processes all CFM frames at its level and drops
CFM frames at lower levels except traffic going to the other lower-level down MEP. The MEP
transparently forwards all CFM frames at a higher level, regardless of whether they are received
from the relay or through the wire
•
Maintenance intermediate points (MIPs) are internal to a domain, not at the boundary, and respond
to CFM only when triggered by traceroute and loopback messages. They forward CFM frames
received from MEPs and other MIPs, drop all CFM frames at a lower level (unless MIP filtering is
enabled), and forward all CFM frames at a higher level and at a lower level and regardless of whether
they are received from the relay or wire side. When MIP filtering is enabled, the MIP drops CFM
frames at a lower level. MIPs also catalog and forward continuity check messages (CCMs), but do
not respond to them.
In the first draft of CFM, MIP filtering was always enabled. In draft 8.1, MIP filtering is disabled by
default, and you can configure it to be enabled or disabled. When MIP filtering is disabled, all CFM
frames are forwarded.
You can manually configure a MIP or configure the switch to automatically create a MIP. You can
configure a MEP without a MIP. In case of a configuration conflict, manually created MIPs take
precedence over automatically created MIPs.