This chapter is from the book
This chapter is from the book
This chapter is from the book
3.2 Code Introduction
The generic interface structures and initialization code are found in three headers and two C files. The device-specific initialization code described in this chapter is found in three different C files. All eight files are listed in Figure 3.1.
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Figure 3.1. Files discussed in this chapter.
Global Variables
The global variables introduced in this chapter are described in Figure 3.2.
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Figure 3.2. Global variables introduced in this chapter.
SNMP Variables
The Net/3 kernel collects a wide variety of networking statistics. In most chapters we summarize the statistics and show how they relate to the standard TCP/IP information and statistics defined in the Simple Network Management Protocol Management Information Base (SNMP MIB-II). RFC 1213 [McCloghrie and Rose 1991] describe SNMP MIB-II, which is organized into 10 distinct information groups shown in Figure 3.3.
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Figure 3.3. SNMP groups in MIB-II.
Net/3 does not include an SNMP agent. Instead, an SNMP agent for Net/3 is implemented as a process that accesses the kernel statistics in response to SNMP queries through the mechanism described in Section 2.2.
While most of the MIB-II variables are collected by Net/3 and may be accessed directly by an SNMP agent, others must be derived indirectly. MIB-II variables fall into three categories: (1) simple variables such as an integer value, a timestamp, or a byte string; (2) lists of simple variables such as an individual routing entry or an interface description entry; and (3) lists of lists such as the entire routing table and the list of all interface entries.
The ISODE package includes a sample SNMP agent for Net/3. See Appendix B for information about ISODE.
Figure 3.4 shows the one simple variable maintained for the SNMP interface group. We describe the SNMP interface table later in Figure 4.7.
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Figure 3.4. Simple SNMP variable in the interface group.