TCP IP Illustrated

Figure 2530 describes the values for the trap type in

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Unformatted text preview: o be a router. 25.10 Traps All the examples we've looked at so far in this chapter have been from the manager to the agent. As shown in Figure 25.1, it's also possible for the agent to send a trap to the manager, to indicate that something has happened on the agent that the manager might want to know about. Traps are sent to UDP port 162 on the manager. In Figure 25.2 we showed the format of the trap PDU. We'll go through all the fields in this message when we look at some tcpdump output below. Six specific traps are defined, with a seventh one allowing a vendor to implement an enterprisespecific trap. Figure 25.30 describes the values for the trap type in the trap message (Figure 25.2). trap type Name Description 0 coldStart Agent is initializing itself. 1 warmStart Agent is reinitializing itself. linkDown An interface has changed from the up to the down state (Figure 25.18). The first variable in the message identifies the interface. 3 linkUp An interface has changed from the down to the up state (Figure 25.18). The first variable in the message identifies the interface. 4 authenticationFailure A message was received from an SNMP manager with an invalid community. 5 egpNeighborLoss An EGP peer has changed to the down state. The first variable in the messages contains the IP address of the peer. 2 file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/snmp_sim.htm (29 of 33) [12/09/2001 14.47.40] Chapter 25. SNMP: Simple Network Management Protocol 6 enterpriseSpecific Look in the specific code field for information on the trap. Figure 25.30 Trap types. We can see some traps using tcpdump. We'll start the SNMP agent on the system sun and see it generate a coldStart trap. (We tell the agent to send traps to the host bsdi. Although we're not running a manager on bsdi to handle the traps, we can run tcpdump and see what packets get generated. Recall from Figure 25.1 that a trap is sent from the agent to the manager, but there is no acknowledgment sent by the manager, so we don't need a manager to handle the traps.) We then send a request us...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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