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SNMPD.EXAMPLES(5)                                 Net-SNMP                                 SNMPD.EXAMPLES(5)



NAME
       snmpd.examples - example configuration for the Net-SNMP agent

DESCRIPTION
       The  snmpd.conf(5)  man page defines the syntax and behaviour of the various configuration directives
       that can be used to control the operation of the Net-SNMP agent, and the  management  information  it
       provides.

       This  companion  man  page  illustrates these directives, showing some practical examples of how they
       might be used.

AGENT BEHAVIOUR
   Listening addresses
       The default agent behaviour (listing on the standard SNMP UDP port on all interfaces)  is  equivalent
       to the directive:
              agentaddress udp:161
       or simply
              agentaddress 161
       The  agent can be configured to only accept requests sent to the local loopback interface (again lis-tening listening
       tening on the SNMP UDP port), using:
              agentaddress localhost:161     # (udp implicit)
       or
              agentaddress 127.0.0.1     # (udp and standard port implicit)
       It can be configured to accept both UDP and TCP requests (over both IPv4 and IPv6), using:
              agentaddress udp:161,tcp:161,udp6:161,tcp6:161
       Other combinations are also valid.

   Run-time privileges
       The agent can be configured to relinquish any privileged access once it has opened the  initial  lis-tening listening
       tening  ports.   Given  a suitable "snmp" group (defined in /etc/group), this could be done using the
       directives:
              agentuser  nobody
              agentgroup snmp
       A similar effect could be achieved using numeric UID and/or GID values:
              agentuser  #10
              agentgroup #10

   SNMPv3 Configuration
       Rather than being generated pseudo-randomly, the engine ID for the agent could be calculated based on
       the MAC address of the second network interface (eth1), using the directives:
              engineIDType 3 engineIDNic  eth1
       or it could be calculated from the (first) IP address, using:
              engineIDType 1
       or it could be specified explicitly, using:
              engineID "XXX - WHAT FORMAT"

ACCESS CONTROL
   SNMPv3 Users
       The  following  directives  will  create  three  users, all using exactly the same authentication and
       encryption settings:
              createUser me     MD5 "single pass phrase"
              createUser myself MD5 "single pass phrase" DES
              createUser andI   MD5 "single pass phrase" DES "single pass phrase"
       Note that this defines three distinct users, who could be granted different levels of access.  Chang-ing Changing
       ing the passphrase for any one of these would not affect the other two.

       Separate pass phrases can be specified for authentication and encryption:
              createUser onering SHA "to rule them all" AES "to bind them"
       Remember  that these createUser directives should be defined in the /var/db/net-snmp/snmpd.conf file,
       rather than the usual location.

   Traditional Access Control
       The SNMPv3 users defined above can be granted access to the full MIB tree using the directives:
              rouser me
              rwuser onering
       Or selective access to individual subtrees using:
              rouser myself   .1.3.6.1.2
              rwuser andI     system

       Note that a combination repeating the same user, such as:
              rouser onering
              rwuser onering
       should not be used. This would configure the user onering  with  read-only  access  (and  ignore  the
       rwuser entry altogether).  The same holds for the community-based directives.

       The directives:
              rocommunity public
              rwcommunity private
       would  define the commonly-expected read and write community strings for SNMPv1 and SNMPv2c requests.
       This behaviour is not configured by default, and would need to be set up explicitly.

              Note:  It would also be a very good idea to change private to something  a  little  less  pre-dictable! predictable!
                     dictable!

       A slightly less vulnerable configuration might restrict what information could be retrieved:
              rocommunity public   default system
       or the management systems that settings could be manipulated from:
              rwcommunity private  10.10.10.0/24
       or a combination of the two.

   VACM Configuration
       This last pair of settings are equivalent to the full VACM definitions:
              #         sec.name  source        community
              com2sec   public    default       public
              com2sec   mynet     10.10.10.0/24 private
              com2sec6  mynet     fec0::/64     private

              #                  sec.model  sec.name
              group  worldGroup  v1         public
              group  worldGroup  v2c        public
              group  myGroup     v1         mynet
              group  myGroup     v2c        mynet

              #              incl/excl   subtree     [mask]
              view   all     included    .1
              view   sysView included    system

              #              context model level   prefix  read    write  notify (unused)
              access  worldGroup  ""  any  noauth  exact   system  none   none
              access  myGroup     ""  any  noauth  exact   all     all    none

       There are several points to note in this example:

       The group directives must be repeated for both SNMPv1 and SNMPv2c requests.

       The com2sec security name is distinct from the community string that is mapped to it. They can be the
       same ("public") or different ("mynet"/"private") - but what appears in the  group  directive  is  the
       security name, regardless of the original community string.

       Both of the view directives are defining simple OID subtrees, so neither of these require an explicit
       mask.  The same holds for the "combined subtree2 view defined below.  In fact, a mask field  is  only
       needed  when defining row slices across a table (or similar views), and can almost always be omitted.

       In general, it is advisible not to mix traditional and VACM-based access configuration  settings,  as
       these  can  sometimes  interfere  with  each  other in unexpected ways.  Choose a particular style of
       access configuration, and stick to it.

   Typed-View Configuration
       A similar configuration could also be configured as follows:
              view   sys2View included    system
              view   sys2View included    .1.3.6.1.2.1.25.1

              authcommunity read       public  default      -v sys2View
              authcommunity read,write private 10.10.10.0/8

       This mechanism allows multi-subtree (or other non-simple) views to be used with the one-line rocommu-nity rocommunity
       nity style of configuration.

       It would also support configuring "write-only" access, should this be required.

SYSTEM INFORMATION
   System Group
       The  full  contents of the 'system' group (with the exception of sysUpTime) can be explicitly config-ured configured
       ured using:
              # Override 'uname -a' and hardcoded system OID - inherently read-only values
              sysDescr     Universal Turing Machine mk I
              sysObjectID  .1.3.6.1.4.1.8072.3.2.1066

              # Override default values from 'configure' - makes these objects read-only
              sysContact   Alan.Turing@pre-cs.man.ac.uk
              sysName      tortoise.turing.com
              sysLocation  An idea in the mind of AT

              # Standard end-host behaviour
              sysServices  72

   Host Resources Group
       The list of devices probed for potential inclusion in the hrDiskStorageTable (and hrDeviceTable)  can
       be amended using any of the following directives:
              ignoredisk /dev/rdsk/c0t2d0
       which prevents the device /dev/rdsk/c_t2d_ from being scanned,
              ignoredisk /dev/rdsk/c0t[!6]d0
              ignoredisk /dev/rdsk/c0t[0-57-9a-f]d0
       either of which prevents all devices /dev/rdsk/c_tXd_ (except .../c_t6d_) from being scanned,
              ignoredisk /dev/rdsk/c1*
       which prevents all devices whose device names start with /dev/rdsk/c1 from being scanned, or
              ignoredisk /dev/rdsk/c?t0d0
       which prevents all devices /dev/rdsk/cXt_d_ (where 'X' is any single character) from being scanned.

   Process Monitoring
       The  list  of  services  running  on a system can be monitored (and provision made for correcting any
       problems), using:
              # At least one web server process must be running at all times
              proc    httpd
              procfix httpd  /etc/rc.d/init.d/httpd restart

              # There should never be more than 1_ mail processes running
              #    (more implies a probable mail storm, so shut down the mail system)
              proc    sendmail   10
              procfix sendmail  /etc/rc.d/init.d/sendmail stop

              # There should be a single network management agent running
              #   ("There can be only one")
              proc    snmpd    1  1
       Also see the "DisMan Event MIB" section later on.

   Disk Usage Monitoring
       The state of disk storage can be monitored using:
              includeAllDisks 10%
              disk /var 20%
              disk /usr  3%
              #  Keep 1__ MB free for crash dumps
              disk /mnt/crash  100000

   System Load Monitoring
       A simple check for an overloaded system might be:
              load 10
       A more refined check (to allow brief periods of heavy use, but recognise sustained medium-heavy load)
       might be:
              load 30 10 5

   Log File Monitoring
       TODO
              file FILE [MAXSIZE]
              logmatch NAME PATH CYCLETIME REGEX

ACTIVE MONITORING
   Notification Handling
       Configuring the agent to report invalid access attempts might be done by:
              authtrapenable 1
              trapcommunity  public
              trap2sink      localhost
       Alternatively,  the  second and third directives could be combined (and an acknowledgement requested)
       using:
              informsink     localhost  public
       A configuration with repeated sink destinations, such as:
              trapsink       localhost
              trap2sink      localhost
              informsink     localhost
       should NOT be used, as this will cause multiple copies of each trap to  be  sent  to  the  same  trap
       receiver.

       TODO - discuss SNMPv3 traps
              trapsess  snmpv3 options  localhost:162

       TODO - mention trapd access configuration


   DisMan Event MIB
       The  simplest  configuration for active self-monitoring of the agent, by the agent, for the agent, is
       probably:
              # Set up the credentials to retrieve monitored values
              createUser    _internal MD5 "the first sign of madness"
              iquerySecName _internal
              rouser        _internal

              # Active the standard monitoring entries
              defaultMonitors         yes
              linkUpDownNotifications yes

              # If there's a problem, then tell someone!
              trap2sink localhost

       The first block sets up a suitable user for retrieving the information to  by  monitored,  while  the
       following pair of directives activates various built-in monitoring entries.

       Note  that  the  DisMan  directives are not themselves sufficient to actively report problems - there
       also needs to be a suitable destination configured to actually send the resulting notifications to.

       A more detailed monitor example is given by:
              monitor -u me -o hrSWRunName "high process memory" hrSWRunPerfMem > 10000

       This defines an explicit boolean monitor entry, looking for any  process  using  more  than  10MB  of
       active memory.  Such processes will be reported using the (standard) DisMan trap mteTriggerFired, but
       adding an extra (wildcarded) varbind hrSWRunName.

       This entry also specifies an explicit user (me, as defined earlier) for retrieving the monitored val-ues, values,
       ues, and building the trap.

       Objects  that  could  potentially  fluctuate  around the specified level are better monitored using a
       threshold monitor entry:
              monitor -D -r 10 "network traffic" ifInOctets 1000000 5000000

       This will send a mteTriggerRising trap whenever the incoming traffic rises above (roughly)  500  kB/s
       on  any  network  interface,  and a corresponding mteTriggerFalling trap when it falls below 100 kB/s
       again.

       Note that this monitors the deltas between successive samples (-D) rather than the actual sample val-ues values
       ues themselves.  The same effect could be obtained using:
              monitor -r 10 "network traffic" ifInOctets - - 1000000 5000000

       The linkUpDownNotifications directive above is broadly equivalent to:
              notificationEvent  linkUpTrap    linkUp   ifIndex ifAdminStatus ifOperStatus
              notificationEvent  linkDownTrap  linkDown ifIndex ifAdminStatus ifOperStatus

              monitor  -r 60 -e linkUpTrap   "Generate linkUp"   ifOperStatus != 2
              monitor  -r 60 -e linkDownTrap "Generate linkDown" ifOperStatus == 2

       This  defines  the traps to be sent (using notificationEvent), and explicitly references the relevant
       notification in the corresponding monitor entry (rather than using the default DisMan traps).

       The defaultMonitors directive above is equivalent to a series of (boolean) monitor entries:
              monitor   -o prNames      -o prErrMessage  "procTable" prErrorFlag   != 0
              monitor   -o memErrorName -o memSwapErrorMsg "memory"  memSwapError  != 0
              monitor   -o extNames     -o extOutput     "extTable"  extResult     != 0
              monitor   -o dskPath      -o dskErrorMsg   "dskTable"  dskErrorFlag  != 0
              monitor   -o laNames      -o laErrMessage  "laTable"   laErrorFlag   != 0
              monitor   -o fileName     -o fileErrorMsg  "fileTable" fileErrorFlag != 0
       and will send a trap whenever any of these entries indicate a problem.

       An alternative approach would be to automatically invoke the corresponding "fix" action:
              setEvent   prFixIt  prErrFix = 1
              monitor -e prFixIt "procTable" prErrorFlag   != 0
       (and similarly for any of the other defaultMonitor entries).

   DisMan Schedule MIB
       The agent could be configured to reload its configuration once an hour, using:
              repeat 3600 versionUpdateConfig.0 = 1

       Alternatively this could be configured to be run at specific times of day (perhaps following rotation
       of the logs):
              cron 10 0 * * * versionUpdateConfig.0 = 1

       The  one-shot style of scheduling is rather less common, but the secret SNMP virus could be activated
       on the next occurance of Friday 13th using:
              at   13 13 13 * 5 snmpVirus.0 = 1

EXTENDING AGENT FUNCTIONALITY
   Arbitrary Extension Commands
       Old Style
              exec [MIBOID] NAME PROG ARGS"
              sh   [MIBOID] NAME PROG ARGS"
              execfix NAME PROG ARGS"
       New Style
              extend [MIBOID] NAME PROG ARGS"
              extendfix [MIBOID] NAME PROG ARGS"

   MIB-Specific Extension Commands
       One-Shot
              "pass [-p priority] MIBOID PROG"

              Persistent
              "pass_persist [-p priority] MIBOID PROG"

   Embedded Perl Support
       If embedded perl support is enabled in the agent, the default initialisation  is  equivalent  to  the
       directives:
              disablePerl  false
              perlInitFile /usr/share/snmp/snmp_perl.pl
       The main mechanism for defining embedded perl scripts is the perl directive.  A very simple (if some-what somewhat
       what pointless) MIB handler could be registered using:
              perl use Data::Dumper;
              perl sub myroutine  { print "got called: ",Dumper(@_),"\n"; }
              perl $agent->register('mylink', '.1.3.6.1.8765', \&myroutine);

       This relies on the $agent object, defined in the example snmp_perl.pl file.

       A more realistic MIB handler might be:
              XXX - WHAT ???
       Alternatively, this code could be stored in an external file, and loaded using:
              perl 'do /usr/share/snmp/perl_example.pl';

   Dynamically Loadable Modules
       TODO
              dlmod NAME PATH"

   Proxy Support
       A configuration for acting as a simple proxy for two other SNMP agents (running  on  remote  systems)
       might be:
              com2sec -Cn rem1context  rem1user default  remotehost1
              com2sec -Cn rem2context  rem2user default  remotehost2

              proxy -Cn rem1context  -v 1 -c public  remotehost1  .1.3
              proxy -Cn rem2context  -v 1 -c public  remotehost2  .1.3
       (plus suitable access control entries).

       The  same  proxy directives would also work with (incoming) SNMPv3 requests, which can specify a con-text context
       text directly.  It would probably be more sensible to use contexts of remotehost1 and  remotehost2  -the remotehost2the
       the names above were chosen to indicate how these directives work together.

       Note that the administrative settings for the proxied request are specified explicitly, and are inde-pendent independent
       pendent of the settings from the incoming request.

       An alternative use for the proxy directive is to pass part of the OID tree to another  agent  (either
       on a remote host or listening on a different port on the same system), while handling the rest inter-nally: internally:
       nally:
              proxy -v 1 -c public  localhost:6161  .1.3.6.1.4.1.99
       This mechanism can be used to link together two separate SNMP agents.

       A less usual approach is to map one subtree into a different area of the  overall  MIB  tree  (either
       locally or on a remote system):
              # uses SNMPv3 to access the MIB tree .1.3.6.1.2.1.1 on 'remotehost'
              # and maps this to the local tree .1.3.6.1.3.1_
              proxy -v 3 -l noAuthNoPriv -u user remotehost .1.3.6.1.3.10 .1.3.6.1.2.1.1

   SMUX Sub-Agents
              smuxsocket 127.0.0.1
              smuxpeer .1.3.6.1.2.1.14 ospf_pass

   AgentX Sub-Agents
       The Net-SNMP agent could be configured to operate as an AgentX master agent (listening on a non-stan-dard non-standard
       dard named socket, and running using the access privileges defined earlier), using:
              master agentx
              agentXSocket /tmp/agentx/master
              agentXPerms  0660 0550 nobody snmp
       A sub-agent wishing to connect to this master agent would need the same  agentXSocket  directive,  or
       the equivalent code:
              netsnmp_ds_set_string(NETSNMP_DS_APPLICATION_ID, NETSNMP_DS_AGENT_X_SOCKET,
                                    "/tmp/agentx/master");

       A loopback networked AgentX configuration could be set up using:
              agentXSocket   tcp:localhost:705
              agentXTimeout  5
              agentXRetries  2
       on the master side, and:
              agentXSocket   tcp:localhost:705
              agentXTimeout  10
              agentXRetries  1
              agentXPingInterval 600
       on the client.

       Note  that the timeout and retry settings can be asymmetric for the two directions, and the sub-agent
       can poll the master agent at regular intervals (600s = every 10 minutes), to ensure the connection is
       still working.

OTHER CONFIGURATION
              override sysDescr.0 octet_str "my own sysDescr"
              injectHandler stash_cache NAME table_iterator

FILES
       /etc/snmp/snmpd.conf

SEE ALSO
       snmpconf(1),   snmpd.conf(5),  snmp.conf(5),  snmp_config(5),  snmpd(8),  EXAMPLE.conf,  netsnmp_con-fig_api(3). netsnmp_config_api(3).
       fig_api(3).



V5.6                                             13 Oct 2006                               SNMPD.EXAMPLES(5)