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Definition 4-1. The ASN.1 definition of SNMP
RFC1157-SNMP DEFINITIONS ::= BEGIN IMPORTS ObjectName, ObjectSyntax, NetworkAddress, IpAddress, TimeTicks FROM RFC1155-SMI; -- top-level message Message ::= SEQUENCE { version -- version-1 for this RFC INTEGER { version-1(0) }, community -- community name OCTET STRING, data -- e.g., PDUs if trivial ANY -- authentication is being used } -- protocol data units PDUs ::= CHOICE { get-request GetRequest-PDU, get-next-request GetNextRequest-PDU, get-response GetResponse-PDU, set-request SetRequest-PDU, trap Trap-PDU } -- PDUs GetRequest-PDU ::= [0] IMPLICIT PDU GetNextRequest-PDU ::= [1] IMPLICIT PDU GetResponse-PDU ::= [2] IMPLICIT PDU SetRequest-PDU ::= [3] IMPLICIT PDU PDU ::= SEQUENCE { request-id INTEGER, error-status -- sometimes ignored INTEGER { noError(0), tooBig(1), noSuchName(2), badValue(3), readOnly(4), genErr(5) }, error-index -- sometimes ignored INTEGER, variable-bindings -- values are sometimes ignored VarBindList } Trap-PDU ::= [4] IMPLICIT SEQUENCE { enterprise -- type of object generating -- trap, see sysObjectID in [5] OBJECT IDENTIFIER, agent-addr -- address of object generating NetworkAddress, -- trap generic-trap -- generic trap type INTEGER { coldStart(0), warmStart(1), linkDown(2), linkUp(3), authenticationFailure(4), egpNeighborLoss(5), enterpriseSpecific(6) }, specific-trap -- specific code, present even INTEGER, -- if generic-trap is not -- enterpriseSpecific time-stamp -- time elapsed between the last TimeTicks, -- (re-)initialization of the network -- entity and the generation of the trap variable-bindings -- interesting information VarBindList } -- variable bindings VarBind ::= SEQUENCE { name ObjectName, value ObjectSyntax } VarBindList ::= SEQUENCE OF VarBind END
This chapter has explored the structure of the SNMP messages and looked at some examples of various SNMP PDUs. The Internet Engineering Task Force (IETF) has enhanced SNMP by adding support for new PDUs, security and other features. These enhancements are part of SNMP version 2, which will be discussed in the next chapter.
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