TCP IP Illustrated

In this section well look at those data types without

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Unformatted text preview: OK 1 tooBig agent could not fit reply into a single SNMP message 2 noSuchName operation specified a nonexistent variable 3 badValue a set operation specified an invalid value or syntax 4 readonly manager tried to modify a read-only variable 5 genErr some other error Figure 25.4 SNMP error status values. If an error occurred, the error index is an integer offset specifying which variable was in error. It is set by the agent only for the noSuchName, badValue, and readonly errors. A list of variable names and values follows in the get, get-next, and set requests. The value portion is ignored for the get and get-next operators. For the trap operator (a PDU type of 4), the format of the SNMP message changes. We describe the fields in the trap header when we describe this operator in Section 25.10. 25.3 Structure of Management Information SNMP uses only a few different types of data. In this section we'll look at those data types, without worrying about how the data is actually encoded (that is, the bit pattern used to store the data). q q q q q q q INTEGER. Some variables are declared as an integer with no restrictions (e.g., the MTU of an interface), some are defined as taking on specific values (e.g., the IP forwarding flag is 1 if forwarding is enabled or 2 if forwarding is disabled), and others are defined with a minimum and maximum value (e.g., UDP and TCP port numbers are between 0 and 65535). OCTET STRING. A string of 0 or more 8-bit bytes. Each byte has a value between 0 and 255. In the BER encoding used for this data type and the next, a count of the number of bytes in the string precedes the string. These strings are not null-terminated strings. DisplayString. A string of 0 or more 8-bit bytes, but each byte must be a character from the NVT ASCII set (Section 26.4). All variables of this type in the MIB-II must contain no more than 255 characters. (A O-length string is OK.) OBJECT IDENTIFIER. We describe these in the next section. NULL. This indicates that the corresponding variable has no value. It is used, for example, as the value of all the variables in a get or get-next reque...
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