Chapter 10 CFM Commands
Ethernet Switch CLI Reference Guide
50
• MEP port - has the ability to send pro-active connectivity check (CC) packets and get
other MEP port information from neighbor switches’ CC packets within an MA.
• MIP port - only forwards the CC packets.
CFM provides two tests to discover connectivity faults.
• Loopback test - similar to using “ping” in Microsoft DOS mode to check connectivity
from your computer to a host. In a loopback test, a MEP port sends a LBM (Loop Back
Message) to a MIP port and checks for an LBR (Loop Back Response). If no response is
received, there might be a connectivity fault between them.
• Link trace test - similar to using “tracert” in the Microsoft DOS mode to check
connectivity from your computer to a host. A link trace test provides additional
connectivity fault analysis to get more information on where the fault is. In a link trace
test, a MEP port sends a LTM (Link Trace Message) to a MIP port and checks for an LTR
(Link Trace Response). If an MIP or MEP port does not respond to the source MEP, this
may indicate a fault. Administrators can take further action to check the fault and resume
services according to the line connectivity status report.
An example is shown next. A user cannot access the Internet. To check the problem, the
administrator starts the link trace test from A which is an MEP port to B which is also an MEP
port. Each aggregation MIP port between aggregated devices responds to the LTM packets and
also forwards them to the next port. A fault occurs at port C. A discovers the fault since it only
gets the LTR packets from the ports before port C.
Figure 2 MIP and MEP Example
10.2 CFM Term Definition
This section lists the common term definition which appears in this chapter. Refer to User’s
Guide for more detailed information about CFM.
C
(port 17, MIP)
(port 2, MEP)
(port 18, MIP)
B
(port 8, MEP)
A
Table 27 CFM Term Definitions
TERM DESCRIPTION
CFM CFM (Connectivity Fault Management) is used to detect and analyze connectivity
faults in bridged LANs.
MD An MD (Maintenance Domain) is part of a network, where CFM can be done. The
MD is identified by a level number and contains both MEPs and MIPs. The Switch
supports up to eight MD levels (0 ~ 7) in a network. You can create multiple MDs
on one MD level and multiple MA groups in one MD.
MA An MA (Maintenance Association) is a group of MEPs and identified by a VLAN
ID. One MA should belong to one and only one MD group.
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