ZyXEL Communications XS3800-28 Cli Reference Manual page 50

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
13.2 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.
Table 30 CFM Term Definitions
TERM
CFM
MD
MA
MEP
MIP
Connectivity
Check
Chapter 13 CFM Commands
C
A
(port 2, MEP)
(port 18, MIP)
DESCRIPTION
CFM (Connectivity Fault Management) is used to detect and analyze connectivity faults in
bridged LANs.
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.
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.
An MEP (Maintenance End Point) port has the ability to send and reply to the CCMs, LBMs and
LTMs. It also gets other MEP port information from neighbor switches' CCMs in an MA.
An MIP (Maintenance Intermediate Point) port forwards the CCMs, LBMs, and LTMs and replies
the LBMs and LTMs by sending Loop Back Responses (LBRs) and Link Trace Responses (LTRs).
Connectivity Check (CC) enables an MEP port sending Connectivity Check Messages
(CCMs) periodically to other MEP ports. An MEP port collects CCMs to get other MEP
information within an MA.
Ethernet Switch CLI Reference Guide
(port 17, MIP)
B
(port 8, MEP)
50