POSTECH DP&NM Lab

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Net-SNMP

J. Won-Ki Hong

Dept. of Computer Science and Engineering

POSTECH

Tel: 054-279-2244

Email: jwkhong@postech.ac.kr

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Contents

• Net-SNMP Package

• History of Net-SNMP

• Applications of Net-SNMP

• Trap Daemon

• Architecture of Net-SNMP Agent

• How to extend SNMP agents with Net-SNMP

• Net-SNMP URL: www.net-snmp.org

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Net-SNMP Package (1/2)• Net-SNMP is a suite of applications used to

implement SNMPv1, SNMPv2c and SNMPv3 using both IPv4 and IPv6 and includes

• Command-line applications to: – retrieve information from an SNMP-capable device, either

using single requests (snmpget, snmpgetnext), or multiple requests (snmpwalk, snmptable, snmpdelta).

– manipulate configuration information on an SNMP-capable device (snmpset).

– retrieve a fixed collection of information from an SNMP-capable device (snmpdf, snmpnetstat, snmpstatus).

– convert between numerical and textual forms of MIB OIDs, and display MIB content and structure (snmptranslate).

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Net-SNMP Package (2/2)

• A graphical MIB browser (tkmib), using Tk/perl.

• A daemon application for receiving SNMP notifications (snmptrapd).

• An extensible agent for responding to SNMP queries for management information (snmpd).

• A library for developing new SNMP applications, with both C and perl APIs.

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History of Net-SNMP

• Originally based on the Carnegie Mellon University implementation (1992)

• University of California at Davis SNMP extends CMU-SNMP, calls UCD-SNMP (1995)

• UCD-SNMP moves to Net-SNMP in April, 2002 (Web sites also moves from www.ucd-snmp.net to www.net-snmp.net)

• Now, Net-SNMP 5.7 released• More detailed history can be found at

http://www.net-snmp.org/about/history.html

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Applications (1)• Common Options

-c community -v 1 | 2c | 3 -r retries -t timeout -p port

• snmpget [COMMON OPTIONS] [-Cf] OID [OID]... – SNMP application that uses the SNMP GET request to query

for information on a network entity – e.g., snmpget -c public localhost system.sysDescr.0 – Result) system.sysDescr.0 = Linux enterflex2.postech.ac.kr …

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Applications (2)• snmpset [COMMON OPTIONS] OID TYPE VALUE

– SNMP application that uses the SNMP SET request to set information on a network entity

– Type: i (INTEGER), u (UNSIGNED), s (STRING)…– e.g., snmpset -c private -v 1 localhost system.sysContact.0 s

mjchoi@postech.ac.kr

• snmpwalk [APPLICATION OPTIONS] [COMMON OPTIONS] [OID] – SNMP application that uses SNMP GETNEXT requests to

query a network entity – Retrieves lots of data, a part of MIB tree (subtree) at once– e.g., snmpwalk -c public localhost system– Result) system.sysDescr.0 = …

system.sysObjectID.0 = … system.sysUpTime.0 = …

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Applications (3)• snmpstatus [COMMON OPTIONS]

– SNMP application that retrieves several important statistics from a network entity.

– The IP address of the entity. sysDescr.0 / sysUpTime.0 /…– e.g., snmpstatus -c public -v 1 localhost– Result) [127.0.0.1] [Linux enterflex2 .postech . ac .kr 2.4.7-10

#1 Thu Sep 6 17 :27:27 EDT 2001 i386 ]…

• snmptranslate [OPTIONS] OID [OID]... – Application that translates SNMP object identifier values from

their symbolic (textual) forms into their numerical forms– e.g., snmptranslate system.sysUpTime.0 – Result) .1.3.6.1.2.1.1.3.0

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Applications (4)• snmptrap [COMMON OPTIONS] [-Ci] enterprise-oid

agent generic-trap specific-trap uptime [OID TYPE VALUE]– SNMP application that uses the SNMP TRAP operation to send

information to a network manager – Definition)

TRAP-TEST-MIB DEFINITIONS ::= BEGINIMPORTS ucdExperimental FROM UCD-SNMP-MIB;demotraps OBJECT IDENTIFIER ::= { ucdExperimental 990 }demo-trap TRAP-TYPE

STATUS current ENTERPRISE demotraps VARIABLES { sysLocation } DESCRIPTION "This is just a demo" ::= 17

END – e.g., snmptrap –v 1 -c public host TRAP-TEST-MIB::demotraps

localhost 6 17 '' SNMPv2-MIB::sysLocation.0 s "Just here"

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Applications (5)

• Other SNMP applications: – snmpgetnext: retrieving unknown indexed data. – snmpbulkwalk: uses SNMP GETBULK requests to

query a network entity – snmptable: displaying table.– snmpnetstat: symbolically displays the values of

various network-related information retrieved from a remote system using the SNMP protocol

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Trap Daemon

• snmptrapd [OPTIONS][LISTENING ADDRESSES] – SNMP application that receives and logs SNMP

TRAP – the default is to listen on UDP port 162 – snmptrapd is displayed as follows – Result) 1999-11-12 23:26:07 localhost

[127.0.0.1] TRAP-TEST-MIB::demotraps: Enterprise Specific Trap (demo-trap) Uptime: 1 day, 5:34:06 SNMPv2-MIB::sysLocation.0 = "Just here"

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Architecture of SNMP Agent

SNMP

MANAGER

SNMP

MANAGER

Managed System

Mgmt.BackendInterface

Mgmt.BackendInterface

EmbeddedSystem

Application

EmbeddedSystem

Application

SNMP Agent

BER Decoder & Encoder

BER Decoder & Encoder

Message Parser

Message Parser

Operation ProcessorOperation Processor

Message GeneratorMessage Generator

TrapMonitor

TrapMonitor

ConnectionListener

ConnectionListener

Request

Response/ Trap

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How to Extend (1)1. Define a private MIB: Example of Cluster MIB

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How to Extend (2)2. Download net-snmp-5.7.1.tar.gz

3. Decompress the file in your home directory command: gtar xvfz net-snmp-5.7.1.tar.gz

4. Compile default SNMP agent– cd net-snmp-5.7.1– ./configure --prefix=“/usr/local/net-snmp”– make– umask 022– make install

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How to Extend (3)6. Install SNMP perl module for using mib2c

• cd net-snmp-5.7.1• cd perl• perl Makefile.PL -NET-SNMP-CONFIG=“sh ../net-

snmp-config” -NET-SNMP-IN-SOURCE=true • make • make test• make install

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How to Extend (4)7. Compile the private MIB file using mib2c

• cd net-snmp-5.7.1• cd local• mkdir cluster• copy the private mib in the current directory

ex) cp ~mjchoi/cluster.my ./cluster.my• export MIBS=ALL• MIBS=./cluster.my• mib2c -c mib2c.scalar.conf generalInfo• mib2c -c mib2c.scalar.conf currentStatus• mib2c -c mib2c.array-user.conf loadBalancer• mv generalInfo.* cluster• mv currentStatus.* cluster• mv loadBalancer.* cluster• cp –r cluster ../agent/mibgroup/.

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How to Extend (5)8. Code the extension agent

• Header file: add necessary definitions• C file

(1) Module definition: the code defining the contents of the MIB

e.g., static oid clusterName_oid[] = { 1, 3, 6, 1, 3, 1, 1, 1, 0 }; (2) Module initialization: initialization before they can start

providing the necessary information

e.g., netsnmp_register_instance(netsnmp_create_handler_registration

("clusterName", do_clusterName, clusterName_oid,

OID_LENGTH(clusterName_oid),

HANDLER_CAN_RWRITE));

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How to Extend (6)8. Code the extension agent

(3) Variable handling: actually handles a request for a particular variable instance e.g., char clusterName[NAME_LEN];

int *var_len; (4) Non-table-based modules: the request handling routine is to

retrieve any necessary scalar data e.g.,

switch (reqinfo->mode) { case MODE_GET: snmp_set_var_typed_value(requests->requestvb, ASN_OCTET_STR, (u_char *) clusterName, var_len); break;

… }

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How to Extend (7)8. Code the extension agent

(5) Simple tables: process a simple table with limited table indexe.g., int serviceTable_handler(netsnmp_mib_handler *handler, netsnmp_handler_registration *reginfo, netsnmp_agent_request_info *reqinfo, netsnmp_request_info *requests) { … switch (reqinfo->mode) { case MODE_GET: switch (table_info->colnum) { case COLUMN_SRINDEX: snmp_set_var_typed_value(var, ASN_INTEGER, …);

break; … } … } …}

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How to Extend (8)8. Code the extension agent

(6) General tables: process a general table, which the maximum index is not determinable e.g., Init_{Name}_Entry(); // Perform any necessary initialization while (( index = Get_Next_{Name}_Entry() ) != EndMarker ) { construct OID from vp->name and index compare new OID and request if valid { save current data if finished // exact match, or ordered table break; // so don't look at any more entries } … } …

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How to Extend (9)8. Code the extension agent (7) Set-able object: the handling of SNMPSET

e.g., switch (reqinfo->mode) {… case MODE_SET_ACTION: // XXX: perform the value change here if ( /* XXX: error? */ ) { netsnmp_set_request_error(reqinfo, requests, “error_msg.”); } break; case MODE_SET_COMMIT: // XXX: delete temporary storage if ( /* XXX: error? */ ) { netsnmp_set_request_error(reqinfo, requests, SNMP_ERR_COMMITFAILED); } break; }…

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How to Extend (10)9. Compile the MIB extension and generate SNMP

daemon• ./configure --with-mib-modules=“cluster/generalInfo,

cluster/currentStatus, cluster/loadBalancer”• cd agent• make • ./snmpd –c config_file (ex) ./snmpd –c /etc/snmp/snmpd.conf

– snmpd [OPTIONS] [LISTENING ADDRESSES]

– SNMP agent which binds to a port and awaits requests from SNMP management software.

– collects the requested information and/or performs the requested operations and returns the information to the sender.

– By default, snmpd listens for SNMP requests on UDP port 161.

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How to Extend (11)10.Modify snmpd.conf for SNMP community

# First, map the community name

# sec.name source community

com2sec clusterUser default postech

# Second, map the security name into a group name:

# groupName securityModel securityName

group clusterGroup v1 clusterUser

# Third, create a view for us to let the group have rights to:

# name incl/excl subtree mask(optional)

view mibview included .iso.org.dod.internet

# Finally, grant the group read-only access to the systemview view.

# group context sec.model sec.level prefix read write notif

access clusterGroup "" any noauth exact mibview mibview none

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Good-Luck &

Have Fun!