net-snmp

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Keimyung University

Net-SNMP

Ju Hong Taek

College of Information and Communication

Keimyung University

Tel: 053-580-5234

Email: [email protected]

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Keimyung University

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

• An extensible agent• An SNMP library• tools to get or set information from SNMP age

nts• tools to generate and handle SNMP traps• a Tk/perl mib browser

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History of Net-SNMP

• Originally based on the Carnegie Mellon University implementations

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

• 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 5.1.1 released

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Applications (1)• snmpcmd [Common OPTIONS] AGENT [PARAMETE

RS] – Common command line arguments– Common OPTIONS

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

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

r information on a network entity – Ex) 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)…– ex) snmpset -c private -v 1 localhost system.sysContact.0 s mj

[email protected]

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

y a network entity – Retrieves lots of data, a part of MIB tree (subtree) at once– Ex) 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 /…– Ex) snmpstatus -c public -v 1 localhost– Result) [127.0.0.1] [Linux enterflex2 .postech . ac .kr 2.4.7-1

0 #1 Thu Sep 6 17 :27:27 EDT 2001 i386 ]…

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

heir symbolic (textual) forms into their numerical forms– Ex) 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 ag

ent 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 – Ex) snmptrap –v 1 -c public host TRAP-TEST-MIB::demotraps localhos

t 6 17 '' SNMPv2-MIB::sysLocation.0 s "Just here"

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Applications (5)

• Etc. – snmpgetnext: retrieving unknown indexed data. – snmpbulkwalk :uses SNMP GETBULK requests to q

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

ous 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 TR

AP – 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-5.0.8.tar.gz

3. Decompress the file in your home directory command: gtar xvfz net-snmp-5.0.8.tar.gz

4. Compile default SNMP agent– cd net-snmp-5.0.8– ./configure --prefix=“/usr/local/net-snmp”– make– make install

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

• cd net-snmp-5.0.8• 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-5.0.8• cd local• mkdir cluster• copy the private mib in the current directory e

x) 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 provi

ding 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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(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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(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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(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 daemo

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

entStatus, 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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