Use SNMP Trace Operations to Monitor a Router

Purpose

Tracing operations record more detailed messages about the operation of SNMP, such as the various types of routing protocol packets sent and received, and routing policy actions. In this topic, traceoptions are configured on a router, a MIB object is queried through a network management station, and the action of the query is verified with a log file on the router.

Note: Traceoptions, in general, requires extra router resources. It is recommended that you do not leave it on permanently.

To use SNMP traceoptions to monitor a router, follow these steps:

Configure Trace Operations for SNMP

Purpose

Define tracing for SNMP to access more granular information about the packets sent and received through SNMP.

Action

To configure SNMP tracing operations, follow these steps:

In configuration mode, go to the following hierarchy level:
[edit]user@R1# edit snmp
Configure trace operations:
[edit snmp]user@R1# set traceoptions flag pdu
Commit the configuration:
user@R1# commit and-quit commit completeExiting configuration mode

Sample Output

user@R1> show configuration
snmp

view all {
    oid .1 include;
}
view system {
    oid system;
}
community public {
    view all;
    authorization read-only;
}
community private {
    view system;
    authorization read-write;
}
traceoptions {
    flag pdu;
}

Meaning

The sample output shows a configuration for SNMP that includes traceoptions. The pdu flag is configured, which results in the generation of SNMP request and response packets. The output for the tracing operation is placed into various log files in the /var/log directory.

Protocol-specific tracing operations override any equivalent operations that you specify in the global traceoptions statement. If there are no equivalent operations, they supplement the global tracing options. If you do not specify any protocol-specific tracing, the routing protocol inherits all the global tracing operations.

Query a MIB With SNMPGet

Purpose

Send an SNMP request to check that the SNMP configuration is correct.

Action

To query a MIB with SNMPGet, enter the following command:

user@nms % snmpget hostname community oid

Sample Output

user-nms % snmpget tp1 public .1.3.6.1.2.1.1.1.0
system.sysDescr.0 = m7i internet router, kernel 6.0R1.5

user-nms % snmpget tp1 public sysDescr.0
system.sysDescr.0 = m7i internet router, kernel 6.0R1.5

Meaning

The sample output shows a query from a network management station (nms) for the description of the system running on the router tp1. The OID is entered in numerical form in the command line, and a description (sysDescr.0) is obtained in the output. You can also use sysDescr.0 in the command line to obtain the same output.

Display the Output for SNMP Trace Operations

Purpose

The SNMP log file shows more granular information about the packets sent and received through SNMP. In this step, the contents of the SNMP log file snmpd are displayed to verify that both the GetRequest and the GetResponse packets appear in the output.

Action

To display the output for trace operations, enter the following Junos OS command-line interface operational mode command:

user@host> show log snmpd

Sample Output

user@R1> show log snmpd [...Output truncated...}
Jan 21 16:32:32 snmpd[28b6fdb3] >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Jan 21 16:32:32 snmpd[28b6fdb3] >>>  Get-Request
Jan 21 16:32:32 snmpd[28b6fdb3] >>>  Source:      172.17.28.131
Jan 21 16:32:32 snmpd[28b6fdb3] >>>  Destination: 10.168.70.143
Jan 21 16:32:32 snmpd[28b6fdb3] >>>  Version: SNMPv1
Jan 21 16:32:32 snmpd[28b6fdb3] >>>  Request_id:  0x28b6fdb3
Jan 21 16:32:32 snmpd[28b6fdb3] >>>  Community:   public
Jan 21 16:32:32 snmpd[28b6fdb3] >>>  Error:     status=0 / vb_index=0
Jan 21 16:32:33 snmpd[28b6fdb3] >>>   OID  : sysDescr.0
Jan 21 16:32:33 snmpd[28b6fdb3] >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<  Get-Response
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<  Source:      10.168.70.143
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<  Destination: 172.17.28.131
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<  Version: SNMPv1
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<  Request_id:  0x28b6fdb3
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<  Community:   public
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<  Error:     status=0 / vb_index=0
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<   OID  : sysDescr.0
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<   type : OctetString
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<    value: "m7i internet router, kernel 6.0R
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<           1.5"
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<   HEX  : 6d 37 69 20  69 6e 74 65
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<          72 6e 65 74  20 72 6f 75
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<          74 65 72 2c  20 6b 65 72
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<          6e 65 6c 20  36 2e 30 52
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<          31 2e 35
Jan 21 16:32:33 snmpd[28b6fdb3]  <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
[...Output truncated...]

Meaning

The sample output shows the contents of the snmpd log file, with all of the packets sent and received through SNMP. The Get-Request packet is sent from a network management station and the Get-Response packet is sent from tp1. The value in the Get-response packet is the same as that returned to the network management station in Step 2, m7i internet router, kernel 6.0R1.5.