学步园

http://www.net-snmp.org/wiki/index.php/TUT:Configuring_snmptrapd

Configuring snmptrapd to allow traps in the door

By default, snmptrapd does not do anything with received notifications. You have to tell it what you want to receive notifications.

Configuring snmptrapd to accept SNMPv1 or SNMPv2c notifications

To receive SNMPv1 or SNMPv2c notifications you need to tell snmptrapd your community strings. The easiest way to do this is by using theauthCommunity snmptrapd.conf configuration file token. For example, this line:

 authCommunity log,execute,net public

Will let snmptrapd process notifications received using the "public" community string. Those notifications may be logged, allowed to trigger executable actions (see below), and resend data to the network (forward).

receive:

snmptrapd -f -C -c /usr/local/net-snmp/share/snmp/snmptrapd.conf -Le -m /usr/mibbrowser/SMM_PETTrap.mib

Send:

snmptrap -v 2c -c public localhost ""  .1.3.6.1.4.1.3183.1.1.0.65797

Configuring snmptrap to accept SNMPv3 notifications

SNMPv3 adds security to the SNMP protocol and is a safer way to receive notification data. But, it's a bit more complex to set up. Configuration of SNMPv3 notifications is described fully on aseparate
page:

Processing Notifications

Generating traps is only half of the battle. We also need somethingto receive the notification, and respond accordingly.The Net-SNMP suite includes an applicationsnmptrapdwhich can accept and process such notifications.

By default, it will simply log all incoming notifications via syslog.The two
snmptrap commands described in
TUT:snmptrap#SNMPv1_Traps:

 $ snmptrap -v 1 -c public host UCD-TRAP-TEST-MIB::demotraps "" 6 17 "" \
       SNMPv2-MIB::sysLocation.0 s "Just here"

and

 $ snmptrap -v 2c -c public host "" UCD-NOTIFICATION-TEST-MIB::demoNotif \
       SNMPv2-MIB::sysLocation.0 s "Just here"

would be logged as:

 1999-11-12 23:26:07 localhost [127.0.0.1] UCD-TRAP-TEST-MIB::demotraps:
       Enterprise Specific Trap (demoTrap) Uptime: 1 day, 5:34:06
       SNMPv2-MIB::sysLocation.0 = "Just here"

and

 1999-11-13 08:31:33 localhost [127.0.0.1]:
       SNMPv2-MIB::sysUpTime.0 = Timeticks: (13917129) 1 day, 14:39:31.29
       SNMPv2-MIB::snmpTrapOID.0 = OID: UCD-NOTIFICATION-TEST-MIB::demoNotif
       SNMPv2-MIB::sysLocation.0 = "just here" 

respectively (MIB is defined in
TUT:snmptrap#Trap_Definitions).

Trap Handlers

The snmptrapd utility also has the ability to execute other programs on the receptionof a trap. This is controlled by the traphandle directive, with the syntax

 traphandle OID command

Notice, that this only takes an OID to determine which trap (or notification) is received. This means that SNMPv1 traps, which have atrap type and
specific type, need to be represented in SNMPv2 format, which is described inRFC 2089.

Matching SNMPv1 OIDs

SNMPv1 traps fall into two broad categories: generic and enterprise specific. Generic traps usetrap types 0 through 5, and do not use the
specific type. To match a generic trap, the traphandle OID should be the SNMPv2-MIB::snmpTraps OID, with an additional final OID of thetrap type + 1. For example, to match linkDown traps (trap type 2), the correct OID would be "1.3.6.1.6.3.1.1.5.3"
(or SNMPv2-MIB::snmpTraps.3, which is also IF-MIB::linkDown).

 SNMPv2-MIB::snmpTraps   1.3.6.1.6.3.1.1.5
  SNMPv2-MIB::coldStart             1.3.6.1.6.3.1.1.5.1
  SNMPv2-MIB::warmStart             1.3.6.1.6.3.1.1.5.2
  IF-MIB::linkDown                  1.3.6.1.6.3.1.1.5.3
  IF-MIB::linkUp                    1.3.6.1.6.3.1.1.5.4
  SNMPv2-MIB::authenticationFailure 1.3.6.1.6.3.1.1.5.5

When the trap type is 6, the trap is an enterprise specific trap. When matching these traps, the traphandle OID is constructed using the enterprise OID andspecific type specified in the trap. Earlier in the tutorial, we sent a
SNMPv1 enterprise specific trap with an enterprise OID of UCD-TRAP-TEST-MIB::demotraps, atrap type of 6 and a
specific type of 17. To match this trap type, the traphandle OID should be the enterprise OID, plus 0, plus thespecific type. So the correct OID would be ".1.3.6.1.4.1.2021.13.990.0.17" (or UCD-TRAP-TEST-MIB::demoTrap).

Matching SNMPv2 OIDs

SNMPv2 traps and informs are much easier, because they include the correct OID in the SNMPv2-MIB::snmpTrapOID.0 variable in the trap.

Example handler script

The command specifies a command to be executed by snmptrapd upon reception by the command. This command is executed with the data of the trap as its standard input. The first line is the host name, the second the IP address of the trap sender, and the following
lines consists of an OID VALUE pair with the data from the received trap.

A simple shell script to be called from snmptrapd is the following:

 #!/bin/sh
 
 read host
 read ip
 vars=
 
 while read oid val
 do
   if [ "$vars" = "" ]
   then
     vars="$oid = $val"
   else
     vars="$vars, $oid = $val"
   fi
 done
 
 echo trap: $1 $host $ip $vars

Now, given the following sample snmptrapd.conf file,

 # the generic traps
 traphandle SNMPv2-MIB::coldStart    /home/nba/bin/traps cold
 traphandle SNMPv2-MIB::warmStart    /home/nba/bin/traps warm
 traphandle IF-MIB::linkDown         /home/nba/bin/traps down
 traphandle IF-MIB::linkUp           /home/nba/bin/traps up
 traphandle SNMPv2-MIB::authenticationFailure /home/nba/bin/traps auth
 # this one is deprecated
 traphandle .1.3.6.1.6.3.1.1.5.6     /home/nba/bin/traps egp-neighbor-loss
 
 # enterprise specific traps
 traphandle UCD-TRAP-TEST-MIB::demoTrap /home/nba/bin/traps demo-trap
 traphandle UCD-NOTIFICATION-TEST-MIB::demoNotif /home/nba/bin/traps demo-notif

The following snmptrap invocation, to issue a generic Link down trap (OID 1.3.6.1.6.3.1.1.5.3),

 % snmptrap -v 1 -c public localhost TRAP-TEST-MIB::demotraps localhost 2 0 "" \
       IF-MIB::ifIndex i 1

results in the following output from snmptrapd:

 1999-11-13 12:46:49 localhost [127.0.0.1]  TRAP-TEST-MIB::traps:
       Link Down Trap (0) Uptime: 1 day, 18:54:46.27
       IF-MIB::ifIndex.0 = 1

and the following output from the handler:

 trap: down localhost 127.0.0.1 SNMPv2-MIB::sysUpTime = 1:18:54:46.27, SNMPv2-MIB::snmpTrapOID = IF-MIB::linkDown, IF-MIB::ifIndex.0 = 1, SNMPv2-MIB::snmpTrapEnterprise = TRAP-TEST-MIB::traps

and issuing our enterprise specific trap (.1.3.6.1.4.1.2021.13.990.0.17) gives this output from our handler:

 trap: demoTrap localhost 127.0.0.1 SNMPv2-MIB::sysUpTime = 1:19:00:48.01, SNMPv2-MIB::snmpTrapOID = UCD-TRAP-TEST-MIB::demoTrap, SNMPv2-MIB::sysLocation.0 = "just here", SNMPv2-MIB::snmpTrapEnterprise = UCD-TRAP-TEST-MIB::traps

and finally our enterprise specific notification:

 trap: demoNotif localhost 127.0.0.1 SNMPv2-MIB::sysUpTime.0 = 1:19:02:06.33, SNMPv2-MIB::snmpTrapOID.0 = UCD-NOTIFICATION-TEST-MIB::demoNotif, SNMPv2-MIB::sysLocation.0 = "just here"