Subject: Telecom Network Management

Topic: OSI Network Management

Difficulty: Medium

TRAPs:

SNMP traps enable an agent to notify the management station of significant events by way of an unsolicited SNMP message.

In this diagram, the setup on the left shows a network management system that polls information and gets a response. The setup on the right shows an agent that sends an unsolicited or asynchronous trap to the network management system (NMS).

There are three types of traps— generic-trap, specific-trap, and time-stamp, which are application specific.

• The generic-trap type consists of coldSrart,warmStan, linkDown,linkUp, authenticationFailure, egpNeighborLoss, and enterpriseSpecific.

• The specific-trap is a specific code and is generated even when an enterpriseSpecific trap is not present. An example of this would be to gather statistics whenever a particular event occurs, such as use by a particular group.

• The time-stamp trap is the time elapsed between the last initialization or re-initialization of the element and the generation of the trap.

The generic-trap field may take on one of seven values:

i. coldStart (0): The sending SNMP entity is reinitializing itself such that the agent's configuration or the protocol entity implementation may be altered. Typically, this is an unexpected restart due to a crash or major fault.

ii. warmStart (1): The sending SNMP entity is reinitializing itself such that neither the agent's configuration nor the protocol entity implementation is altered. Typically, this is a routine restart.

iii. linkDown (2): signals a failure in one of the communications links of the agent. The first element in the variablebindings field is the name and value of the ifIndex instance for the referenced interface.

iv. linkUp (3): signals that one of the communications links of the agent has come up. The first element in the variablebindings field is the name and value of the if Index instance for the referenced interface.

v. authenticationFailure (4): This signals that the sending protocol entity has received a protocol message that has failed authentication.

vi. egpNeighborLoss (5): This signals that an EGP neighbor for whom the sending protocol entity was an EGP peer has been marked down and the peer relationship no longer exists.

vii. enterpriseSpecific (6): signifies that the sending protocol entity recognizes that some enterprise-specific event has occurred. The specific-trap field indicates the type of trap. Unlike the GetRequest, GetNextRequest, and SetRequest PDUs, the Trap PDU does not elicit a response from the other side.

Trap PDU:

The Trap PDU is issued by an SNMP entity on behalf of a network management agent application. It is used to provide the management station with an asynchronous notification of some significant event. Its format is quite different from that of the other SNMP PDUs. The fields are

• PDU type: indicating that this is a Trap PDU

• enterprise: identifies the network management subsystem that generated the trap (Its value is taken from sysObject ID in the System group.)

• agent -addr: the IP address of the object generating the trap

• generic-trap: one of the predefined trap types

• specific -trap: a code that indicates more specifically the nature of the trap

• time-stamp: the time between the last (re)initialization of the network entity that issued the trap and the generation of the trap

• variablebindings: additional information relating to the trap (The significance of this field is implementation-specific.) Trap parameter Description

TimeStamp:

Indicates the number of hundredths of a second that have elapsed since the (re)start of the SNMP agent and the sending of the trap. It shows the value of the MIB-II variable sysUpTime converted into hours, minutes and seconds. (MIB-II is a more recent version of MIB, which caters for more detailed information on managed objects)

Enterprise Generic Type:
Shows the OID of the management enterprise that defines the trap message. The Generic type value is categorised and numbered 0 to 6:

0 = coldStart, 1 = warmStart, 2 = linkDown, 3 = linkUp,4 = authenticationFailure, 5 = egpNeighborLoss; the trap type value 6 is identified as an enterprise-specific value. This field shows the value based on the type of trap.

Specific Type:

The specific trap type indicates the specific trap as defined in an enterprise-specific MIB. If the Generic type value is 6 then this field shows a value > 0.If the Generic type value is a value other than 6, then the field shows a value 0

• SNMP traps are used in the management of a data network.

• SNMP traps enable an agent to notify the management station of significant events by way of an unsolicited SNMP message.

• The Trap PDU is issued by an SNMP entity on behalf of a network management agent application. It is used to provide the management station with an asynchronous notification of some significant event. Its format is quite different from that of the other SNMP PDUs

• There are three types of traps— generic-trap, specific-trap, and time-stamp, which are application specific.

1. The generic-trap type consists of coldSrart,warmStan, linkDown,linkUp, authenticationFailure, egpNeighborLoss, and enterpriseSpecific.

2. The specific-trap is a specific code and is generated even when an enterpriseSpecific trap is not present. An example of this would be to gather statistics whenever a particular event occurs, such as use by a particular group.

3. The time-stamp trap is the time elapsed between the last initialization or re-initialization of the element and the generation of the trap.

• SNMPv1 (Simple Network Management Protocol) and SNMPv2c, along with the associated Management Information Base (MIB), encourage trap-directed notification.

• SNMPv1 traps are defined in RFC 1157, with these fields:

1. Enterprise—Identifies the type of managed object that generates the trap.

2. Agent address—Provides the address of the managed object that generates the trap.

3. Generic trap type—Indicates one of a number of generic trap types.

4. Specific trap code—Indicates one of a number of specific trap codes.

5. Time stamp—Provides the amount of time that has elapsed between the last network reinitialization and generation of the trap.

6. Variable bindings—The data field of the trap that contains PDU. Each variable binding associates a particular MIB object instance with its current value.

• Standard generic traps are: coldStart, warmStart, linkDown, linkUp, authenticationFailure, egpNeighborLoss.

• For generic SNMPv1 traps, Enterprisefield contains value of sysObjectID of the device that sends trap.

• For vendor specific traps, Generic trap type field is set to enterpriseSpecific.

• In SNMPv2c trap is defined as NOTIFICATION and formatted differently compared to SNMPv1. It has these parameters:

1. sysUpTime—This is the same as Time stamp in SNMPv1 trap.

2. snmpTrapOID —Trap identification field. For generic traps, values are defined in RFC 1907, for vendor specific traps snmpTrapOID is essentially a concatenation of the SNMPv1 Enterprise parameter and two additional sub-identifiers, '0', and the SNMPv1 Specific trap code parameter.

3. VarBindList—This is a list of variable-bindings