System information

392 Observer Suite: SNMP Management
ipAddrEntry OBJECT-TYPE
SYNTAX IpAddrEntry
ACCESS not-accessible
STATUS mandatory
DESCRIPTION
“The addressing information for one of
this entity's IP addresses.”
INDEX { ipAdEntAddr }
::= { ipAddrTable 1 }
IpAddrEntry ::=
SEQUENCE {
ipAdEntAddr
IpAddress,
ipAdEntIfIndex
INTEGER,
ipAdEntNetMask
IpAddress,
ipAdEntBcastAddr
INTEGER
}
Basic Encoding Rules (BER)
BER describes how to convert the values of MIB objects into a format that allows them to
be transferred through a network. The BER specification provides a way to express all
ASN.1 objects in binary format. BER rules are used for object types, object values, and
object IDs. The usual format of a BER-encoded value includes the type field (1 byte),
variable length, and data fields. The consistent format allows multiple objects to be placed
in a single PDU on the transmitting side and decoded on the receiving side.
SNMP Requests
SNMP works by exchanging SNMP requests between a management station and an
SNMP agent. Requests are usually transferred as a data portion of an IP-UDP packet,
although implementations of SNMP exist for TCP, IPX-SPX, and other protocols. For
UDP, the SNMP management station sends requests to the agent over the network to UDP
port number 161. The SNMP message consists of two parts:
• The SNMP header, including SNMP version number, request size information, and a
password (called a community name).
• The block of one or more requested objects combined in the PDU.
There are five different PDU types: GetRequest, GetNextRequest, GetResponse,
SetRequest, and Trap. The first four PDUs have the same format. (The Trap PDU has a
somewhat different format and has a different scope of use). The first three fields of the
first four PDUs identify PDU type, PDU size, and error information. These common fields
are followed by a variable bindings field that includes one or more request or reply
objects.