Diagnostic; Chapter 42 Diagnostic; Diagnostic Overview; What You Can Do In This Chapter - ZyXEL Communications VMG Series User Manual

42.1 Diagnostic Overview

The Diagnostic screens display information to help you identify problems with the Zyxel Device.
The route between a Central Office Very-high-bit-rate Digital Subscriber Line (CO VDSL) switch and one
of its Customer-Premises Equipment (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.

42.1.1 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 42.3 on page
• The 802.1ag screen lets you perform CFM actions
• The 802.3ah screen lets you configure link OAM port
• The OAM Ping screen lets you send an ATM OAM (Operation, Administration and Maintenance)
packet to verify the connectivity of a specific PVC.

42.2 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.

Chapter 42 Diagnostic

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