Net-SNMP
Contents
Net-SNMP Package
History of Net-SNMP
Applications of Net-SNMP
Trap Daemon
How to extend SNMP agents with Net-SNMP
Architecture of Net-SNMP Agent
Package
• An extensible agent
• An SNMP library
• tools to get or set information from SNMP agents
• tools to generate and handle SNMP traps
• a Tk/perl mib browser
History
• Originally based on the
•
• 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 5.0.8 released
Application
• snmpcmd [Common OPTIONS] AGENT [PARAMETERS]
– 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 for information on a network entity
– Ex) snmpget -c public localhost system.sysDescr.0
– Result) system.sysDescr.0 = Linux enterflex2.postech.ac.kr …
• 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 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
– Ex) snmpwalk -c public localhost system
– Result)
system.sysDescr.0 = …
system.sysObjectID.0 = …
system.sysUpTime.0 = …
• snmpstatus [COMMON OPTIONS]
– SNMP application that retrieves several important statistics from a network entity.
– The IP address of the entity. à sysDescr.0 / sysUpTime.0 /…
– Ex) snmpstatus -c public -v 1 localhost
– Result) [127.0.0.1] à[Linux enterflex2 .postech . ac .kr 2.4.7-10 #1 Thu Sep 6
• snmptranslate [OPTIONS] OID [OID]...
– Application that translates SNMP object identifier values from their symbolic (textual) forms into their numerical forms
– Ex) snmptranslate system.sysUpTime.0
– Result) .1.3.6.1.2.1.1.3.0
• 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 ::= BEGIN
IMPORTS ucdExperimental FROM UCD-SNMP-MIB;
demotraps OBJECT IDENTIFIER ::= { ucdExperimental 990 }
demo-trap TRAP-TYPE
STATUS current
VARIABLES { sysLocation }
DESCRIPTION "This is just a demo"
::= 17
END
– Ex) snmptrap –v 1 -c public host TRAP-TEST-MIB::demotraps localhost 6 17 '' SNMPv2-MIB::sysLocation.0 s "Just here"
– Etc.
– 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
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
HOW To Extend
1.Define a private MIB: Example of Cluster MIB
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
① cd net-snmp-5.0.8
② ./configure --prefix=“/usr/local/net-snmp”
③ make
④ make install
5. Install SNMP perl module for using mib2c
① cd net-snmp-5.0.8
② cd perl
③ perl Makefile.PL -NET-SNMP-CONFIG=“sh ../../net-snmp-config” -NET-SNMP-IN-SOURCE=true
④ make
⑤ make test
⑥ make install
6. 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
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/.
8. Code the extension agent
(1) 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));
(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;
…
}
(5) Simple tables: process a simple table with limited table index
e.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;
…
} (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;
}
…
}
…
}
(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
}
…
}
…
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.
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
