Chapter 15 Diagnostic; Overview; What You Can Do In This Chapter; What You Need To Know - ZyXEL Communications VMG4005-B50B User Manual

15.1 Overview

The Diagnostic screen display information to help you identify problems with the VMG.
The route between a CO VDSL switch and one of its CPE may go through switches owned by
independent organizations. A connectivity fault point generally takes time to discover and impacts
subscriber's network access. In order to eliminate the management and maintenance efforts, IEEE
802.1ag is a Connectivity Fault Management (CFM) specification which allows network administrators to
identify and manage connection faults. Through discovery and verification of the path, CFM can
detect, analyze and isolate connectivity faults in bridged LANs.

15.1.1 What You Can Do in this Chapter

The Ping & TraceRoute & NsLookup screen lets you ping an IP address or trace the route packets take to
a host (Section 15.3 on page

15.2 What You Need to Know

The following terms and concepts may help as you read through this chapter.
How CFM Works
A Maintenance Association (MA) defines a VLAN and associated Maintenance End Point (MEP) ports
on the device under a Maintenance Domain (MD) level. An MEP port has the ability to send
Connectivity Check Messages (CCMs) and get other MEP ports information from neighbor devices'
CCMs within an MA.
CFM provides two tests to discover connectivity faults.
• Loopback test - checks if the MEP port receives its Loop Back Response (LBR) from its target after it
sends the Loop Back Message (LBM). If no response is received, there might be a connectivity fault
between them.
• Link trace test - provides additional connectivity fault analysis to get more information on where the
fault is. If an MEP port does not respond to the source MEP, this may indicate a fault. Administrators
can take further action to check and resume services from the fault according to the line
connectivity status report.
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