ZyXEL VMG9823 User Guide - Page 276
Diagnostic
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CHAPTER 38 Diagnostic 38.1 Overview The Diagnostic screens 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. 38.1.1 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 38.3 on page 277). • The 802.1ag screen lets you perform CFM actions (Section 38.4 on page 277). • The OAM Ping screen lets you send an ATM OAM (Operation, Administration and Maintenance) packet to verify the connectivity of a specific PVC. (Section 38.5 on page 278). 38.2 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. VMG9823-B10A User's Guide 276