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The balance of the events (review Trace 7.11a) read and invalidate the alarmTable and eventTable by setting the values of the alarmStatus {rmon 3.1.1.12} and eventStatus {rmon 9.1.1.7} to a value of 4 (invalid).
In summary, this trace has illustrated how the RMON alarm and event groups interact to provide both monitoring and notification of significant network conditions.
To summarize the examples discussed in this chapter, this section looks at two alternatives for accessing the configuration parameters and operational statistics of a remote bridge. One alternative is to access the bridge with a workstation and to access the bridges configuration menus using the Telecommunication Network Protocol (TELNET). TELNET allows a remote user to access a host or device as if it were a local terminal. The second alternative is to access the bridge with the management console using SNMP and retrieve the appropriate MIB information. Lets compare these two methods.
In the first method, a Sun Workstation initiates a TELNET session with the 3Com bridge (see Figure 7-12). The network administrator uses commands defined by 3Com to retrieve the system parameters and statistics. Each of these commands is then sent from the workstation to the bridge in a TELNET message, and the bridge returns a corresponding response. For example, in Frame 1 (see Trace 7.12a), the system version is requested using the 3Com show -sys ver command. The bridge responds with:
SW/NBII-BR-5.0.1, booted on Mon Mar 22 12:05 from local floppy (see Trace 7.12b).
Figure 7-12. Remote device configuration using TELNET and SNMP
Subsequent requests obtain the system contact (Frames 7 through 10), the system location (Frames 11 through 14), and the system name (Frames 15 through 18). The network administrator next accesses the IP Address Translation (ARP) table (Frames 19 through 53) and the IP table (Frames 54 through 65). The final operation retrieves the Path Statistics, such as the number of packets transmitted and received, collisions, and network utilization (Frames 66 through 99). The TELNET method requires the transmission of a total of 99 frames, including 8,599 octets of information.
The second method uses the network management console to access the bridges MIB using SNMP (see Trace 7.12c). The administrator queries the System group (Frames 1 through 4), the Address Translation group (Frames 5 through 18), the IP group (Frames 19 through 22), and the Interfaces group (Frames 23 through 42). The details of these transactions reveal almost identical information as that discovered earlier (see Trace 7.12d). The SNMP method requires the transmission of a total of 42 frames and 8,910 octets of information.
The question, then, is which of these two methods is best? From a network traffic point of view, the results are almost identical: 8,599 octets are transmitted using TELNET, and 8,910 octets using SNMP.
From a practical angle, however, SNMP has an advantage. TELNET requires the network manager to have a workstation available, to understand TELNET commands, and to understand the product-specific parameters, menus, configuration screens, and so on, that are part of that managed system. SNMP does not require these details. The administrator simply goes to the management console, accesses the device in question (the 3Com bridge), and enters well-known SNMP commands. Few details of that bridges internal configuration are necessary. Whats more, SNMP may also use vendor-specific traps to alert the administrator to significant events.
In summary, great synergies can come from using an open network management platform instead of a multitude of vendor-specific solutions. Perhaps this is one reason that SNMP has achieved its great popularity!
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