Simple Network Management Protocol(SNMP)
SNMP (Simple Network Management Protocol) is a network management protocol that provides communication between network devices and network management systems. SNMP is used to monitor the status of network devices, detect errors, evaluate performance, and perform management operations.
To better understand the snmp protocol, I will install a virtual machine on my computer (ubuntu server). From now on i will call my virtual machine as agent computer and my local as admin computer
How do I enable SNMP on Ubuntu? run the following commands in the terminal on the agent computer:
1.Update all packages: sudo apt-get update
2.Install SNMP: sudo apt-get install snmpd
3.Edit the snmpd.conf file with any text editor. Type: sudo nano /etc/snmp/snmpd.conf
4.Configure agentAddress: agentAddress udp:161
5.Configure rocommunity name like: rocommunity public
-Change “public” to your community name
6.Restart the SNMPD service: sudo service snmpd restart
7.Check that SNMPD is started OK with this: sudo service snmpd status
if the output is like this, snmp service is running correctly
MIB is a structure used in network management protocols. A MIB is a collection of data items that describe the state, configuration, and other properties of managed devices. When communicating with SNMP (Simple Network Management Protocol), admin clients use MIB files to get management information from SNMP agents (managed devices).
You can follow the steps below to enable MIBs in Linux operating system:
- Downloading MIB files:
sudo apt-get install snmp-mibs-downloader - Defining MIB files:
sudo nano /etc/snmp/snmp.conf - Add this line inside the file:
mibs +ALLandview all included .1 80 mibs +ALL - You can use the following command to check active MIB files:
snmpwalk -v2c -c public localhost
If this output is output, then the operation is correct.
Creating a customized MIB file is used to define management information for a specific need outside of standard MIB files.
For example, we can create a custom MIB file for the NTP service. This file may contain administrative information of NTP servers, statistics about time synchronization, and configurations. In this way, we can access and manage NTP service related information using this custom MIB file over SNMP protocol.
You can follow the steps below to download ntp service and create custom mib file
1.Downloading NTP:
-You can use this command to download NTP: sudo apt-get install ntp`
2.Creating the custom MIB file:
-To create the custom MIB file, first go to /usr/share/snmp/mibs
-cd /usr/share/snmp/mibs
-Then you can use a text editor to create the custom MIB file. For example, create a new file with the Nano text editor using the following command:
-sudo nano ntp.txt
3.Generating the Contents of the Custom MIB File: Let's open the "ntp.txt" file we created and edit its content as follows:
NTPv4-MIB DEFINITIONS ::= BEGIN
IMPORTS MODULE-IDENTITY,OBJECT-TYPE,Integer32,Unsigned32,enterprises FROM SNMPv2-SMI -- RFC2578
MODULE-COMPLIANCE,OBJECT-GROUP FROM SNMPv2-CONF -- RFC2580
Utf8String
FROM SYSAPPL-MIB; -- RFC2287
ntpSnmpMIB MODULE-IDENTITY
LAST-UPDATED "202203270000Z"
ORGANIZATION "My Organization"
CONTACT-INFO "Email: "
DESCRIPTION "Custom MIB for monitoring NTP service"
REVISION "202203270000Z"
DESCRIPTION "Initial revision"
::= {enterprises 1023 }
ntpSnmpMIBObjects OBJECT IDENTIFIER ::= {ntpSnmpMIB 1 }
ntpEntInfo OBJECT IDENTIFIER ::= { ntpSnmpMIBObjects 1 }
ntpEntStatus OBJECT IDENTIFIER ::= { ntpSnmpMIBObjects 2 }
ntpEntSoftwareName OBJECT-TYPE
SYNTAX Utf8String
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The product name of the running NTP version, e.g. 'ntpd'"
::= { ntpEntInfo 4 }
ntpEntTimeResolution OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The time resolution in integer format, where the resolution
is represented as divisions of a second, e.g. a value of 1000
translates to 1.0 ms."
::= { ntpEntInfo 2 }
ntpEntTimePrecision OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The entity's precision in integer format, shows the precision.
A value of -5 would mean 2^-5 = 31.25 ms"
::= { ntpEntInfo 3 }
ntpStatus OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The synchronization status of the NTP server"
::= {ntpEntStatus 1 }
ntpEntStatusActiveRefSourceId OBJECT-TYPE
SYNTAX Unsigned32 ( 0..99999 )
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The association ID of the current syspeer."
::= { ntpEntStatus 2}
ntpEntConformance OBJECT IDENTIFIER ::= { ntpSnmpMIB 2 }
ntpEntCompliances OBJECT IDENTIFIER ::= { ntpEntConformance 1 }
ntpEntGroups OBJECT IDENTIFIER ::= { ntpEntConformance 2 }
ntpEntNTPCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP entities which use NTP and
implement the NTP MIB"
MODULE -- this module
MANDATORY-GROUPS {
ntpEntObjectsGroup1
}
::= { ntpEntCompliances 1 }
ntpEntSNTPCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP entities which use SNTP and
implement the NTP MIB"
MODULE -- this module
MANDATORY-GROUPS {
ntpEntObjectsGroup1
}
GROUP ntpEntObjectsGroup2
DESCRIPTION
"optional notifications for this MIB"
::= { ntpEntCompliances 2 }
ntpEntObjectsGroup1 OBJECT-GROUP
OBJECTS {
ntpEntSoftwareName
}
STATUS current
DESCRIPTION
"A collection of objects for the NTP MIB."
::= { ntpEntGroups 1 }
ntpEntObjectsGroup2 OBJECT-GROUP
OBJECTS {
ntpEntTimeResolution,
ntpEntTimePrecision,
ntpEntStatusActiveRefSourceId,
ntpStatus
}
STATUS current
DESCRIPTION
"A collection of objects for the NTP MIB."
::= { ntpEntGroups 2 }
END
Now let's add this mib file to /etc/snmp/snmpd.conf asmibs +NTPv4-MIB
In order to validate the MIB structure, we can use smilint.
validate
Run smilint /usr/share/snmp/mibs/ntp.txt
if you don't get any output then mib file is in correct format
The snmptranslate command helps us find OIDs for certain features in NTPv4-MIB.
In order to add new functionality to an SNMP agent the agent must be extended.
https://vincent.bernat.ch/en/blog/2012-extending-netsnmp
Let us create our first script. Create /etc/snmp/exampleScript.sh and add the following content to it:
PLACE=".1.3.6.1.4.1.1023.1.2.1"
REQ="$2" # Requested OID
VALUE_STORAGE="/tmp/snmp_value_storage.txt"
# Check if the value storage file exists, if not, create it
if [ ! -f "$VALUE_STORAGE" ]; then
touch $VALUE_STORAGE
fi
# Function to get value from the value storage
get_value_from_storage() {
OID=$1
grep "^$OID" $VALUE_STORAGE | cut -d' ' -f2
}
# Function to set value to the value storage
set_value_to_storage() {
OID=$1
VALUE=$2
if grep -q "^$OID" $VALUE_STORAGE; then
sed -i "s/^$OID.*/$OID $VALUE/" $VALUE_STORAGE
else
echo "$OID $VALUE" >> $VALUE_STORAGE
fi
}
# Process SET requests by saving the assigned value to the value storage
if [ "$1" = "-s" ]; then
set_value_to_storage $REQ $4
exit 0
fi
# GETNEXT requests - determine next valid instance
if [ "$1" = "-n" ]; then
case "$REQ" in
$PLACE| \
$PLACE.0| \
$PLACE.0.*| \
$PLACE.1) RET=$PLACE.1.0 ;; # netSnmpPassString.0
$PLACE.1.*| \
$PLACE.2| \
$PLACE.2.0| \
$PLACE.2.0.*| \
$PLACE.2.1| \
$PLACE.2.1.0| \
$PLACE.2.1.0.*| \
$PLACE.2.1.1| \
$PLACE.2.1.1.*| \
$PLACE.2.1.2| \
$PLACE.2.1.2.0) RET=$PLACE.2.1.2.1 ;; # netSnmpPassInteger.1
$PLACE.2.1.2.*| \
$PLACE.2.1.3| \
$PLACE.2.1.3.0) RET=$PLACE.2.1.3.1 ;; # netSnmpPassOID.1
$PLACE.2.*| \
$PLACE.3) RET=$PLACE.3.0 ;; # netSnmpPassTimeTicks.0
$PLACE.3.*| \
$PLACE.4) RET=$PLACE.4.0 ;; # netSnmpPassIpAddress.0
$PLACE.4.*| \
$PLACE.5) RET=$PLACE.5.0 ;; # netSnmpPassCounter.0
$PLACE.5.*| \
$PLACE.6) RET=$PLACE.6.0 ;; # netSnmpPassGauge.0
*) exit 0 ;;
esac
else
# GET requests - check for valid instance
case "$REQ" in
$PLACE.1.0| \
$PLACE.2.1.2.1| \
$PLACE.2.1.3.1| \
$PLACE.3.0| \
$PLACE.4.0| \
$PLACE.5.0| \
$PLACE.6.0) RET=$REQ ;;
*) exit 0 ;;
esac
fi
# Process SET requests by saving the assigned value to the value storage
if [ "$1" = "-s" ]; then
case "$REQ" in
$PLACE.3.0) set_value_to_storage $REQ $4; exit 0 ;;
$PLACE.4.0) set_value_to_storage $REQ $4; exit 0 ;;
*) exit 0 ;;
esac
fi
# "Process" GET* requests - return hard-coded value
echo "$RET"
case "$RET" in
$PLACE.1.0) echo "string"; echo "ntp status: active"; exit 0 ;;
$PLACE.2.1.2.1) echo "string"; echo "since Fri ess2023-04-07"; exit 0 ;;
$PLACE.2.1.3.1) echo "integer"; echo "1"; exit 0 ;;
$PLACE.3.0) echo "string"; echo "$(get_value_from_storage $RET '')"; exit 0 ;;
$PLACE.4.0) echo "string"; echo "$(get_value_from_storage $RET '')"; exit 0 ;;
$PLACE.5.0) echo "counter"; echo "42"; exit 0 ;;
$PLACE.6.0) echo "gauge"; echo "42"; exit 0 ;;
*) echo "string"; echo "ack... $RET $REQ"; exit 0 ;; # Should not happen
esac
- get_value_from_storage(): A function used to retrieve a value from the value storage file.
- set_value_to_storage(): A function used to save a value to the value storage file.
- SET requests: The script uses the set_value_to_storage() function to store an assigned value in the value storage file.
- GETNEXT requests: It determines the next valid instance.
- GET requests: It checks for a valid instance.
- Other GET requests: It returns hardcoded values.
add the following line to snmpd.conf
pass .1.3.6.1.4.1.1023.1.2.1 /bin/bash /etc/snmp/exampleScript.sh
and then run the following code:snmpwalk -v2c -c public localhost .1.3.6.1.4.1.1023.1.2
output should be like this
Now we have written the ntp status as active by default in the script file above. Now let's write a c code and this c code will update $PLACE.1.0 as active or incative according to the ntp status.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
// Check NTP status
FILE *pipe = popen("sudo systemctl status ntp", "r");
FILE *output_file = fopen("ntp_status.txt", "w");
if (pipe == NULL || output_file == NULL) {
perror("Error opening pipe or file");
return 1;
}
int found = 0;
char search[] = "active (running)";
char buffer[1024];
char result[1024];
while(fgets(buffer,sizeof(buffer),pipe) !=NULL){
if(strstr(buffer,search)!=NULL){
found=1;
strcpy(result, strchr(buffer, ':') + 5); // copy the part of the line after ':'
fputs("1( active)",output_file);
printf("1(active)");
found=1;
break;}}
if(!found) {
fputs("0(inactive)",output_file);
printf("0(inactive)"); }
pclose(pipe);
fclose(output_file);
// Update the script file
FILE *sh_file = fopen("/etc/snmp/exampleScript.sh", "r+");
if (sh_file == NULL) {
perror("Error opening script file");
return 1;
}
char buffer2[1024];
while (fgets(buffer2, sizeof(buffer2), sh_file)) {
if (strstr(buffer2, " $PLACE.1.0)")) {
if (found == 1) {
fseek(sh_file, -strlen(buffer2), SEEK_CUR);
fprintf(sh_file, " $PLACE.1.0) echo \"string\"; echo \"ntp status: active\"; exit 0 ;;\n"$
fprintf(sh_file, " $PLACE.2.1.2.1 ) echo \"string\"; echo \"since Fri 2023-04-07 \" exit 0 ;;\n"$
fprintf(sh_file, " $PLACE.2.1.3.1) echo \"integer\"; echo \"1\"; exit 0 ;;\n"$
} else {
fseek(sh_file, -strlen(buffer2), SEEK_CUR);
fprintf(sh_file, " $PLACE.1.0) echo \"string\"; echo \"ntp status: inactive\"; exit 0 ;;\n"$
fprintf(sh_file, " $PLACE.2.1.2.1 ) echo \"string\"; echo \"since Fri 2023-04-07 \" exit 0 ;;\n"$
fprintf(sh_file, " $PLACE.2.1.3.1) echo \"integer\"; echo \"0\"; exit 0 ;;\n"$
}
break;
}
}
fclose(sh_file);
return 0;
}
This program runs a shell command to check the NTP status, processes the output, and then updates a script file. The script will return fixed text such as "ntp status: active" or "ntp status: inactive" depending on the specific SNMP OIDs.
Instead of running this c code every time from the terminal, let's write an example service to run it continuously.
Description=Example Service
[Service]
ExecStart=/bin/bash -c "gcc -o /home/polat/hello /home/polat/hello.c && /home/polat/hello"
Restart=always
StartLimitInterval=1min
StartLimitBurst=0
[Install]
WantedBy=multi-user.target
As can be seen in the output, the status of the ntp service is updated automatically.
snmpset is a tool for modifying the manageable properties of a network device using the SNMP (Simple Network Management Protocol) protocol.
snmpwalk -v2c -c public 10.1.240.61 .1.3.6.1.4.1.1023.1.2
When we run the a command, the output is as follows:
hilmi@onur:~$ snmpwalk -v2c -c public 10.1.240.61 .1.3.6.1.4.1.1023.1.2
SNMPv2-SMI::enterprises.1023.1.2.1.1.0 = STRING: "ntp status: active"
SNMPv2-SMI::enterprises.1023.1.2.1.2.1.2.1 = STRING: "since Fri 2023-04-07 exit 0"
SNMPv2-SMI::enterprises.1023.1.2.1.2.1.3.1 = INTEGER: 1
SNMPv2-SMI::enterprises.1023.1.2.1.3.0 = STRING: "ankara, istanbul"
SNMPv2-SMI::enterprises.1023.1.2.1.4.0 = STRING: "aslan, kaplan"
if we want to change oid content of 1023.1.2.1.4.0, We should write a command like the following:
snmpset -v2c -c public 10.1.240.61 .1.3.6.1.4.1.1023.1.2.1.4.0 s "{artvin,rize}"
then when we run the snmpwalk -v2c -c public 10.1.240.61 .1.3.6.1.4.1.1023.1.2 command again, the output changes as follows:
SNMPv2-SMI::enterprises.1023.1.2.1.1.0 = STRING: "ntp status: active"
SNMPv2-SMI::enterprises.1023.1.2.1.2.1.2.1 = STRING: "since Fri 2023-04-07 exit 0"
SNMPv2-SMI::enterprises.1023.1.2.1.2.1.3.1 = INTEGER: 1
SNMPv2-SMI::enterprises.1023.1.2.1.3.0 = STRING: "ankara, istanbul"
SNMPv2-SMI::enterprises.1023.1.2.1.4.0 = STRING: "artvin, rize"
Now let's save the information sent with snmp into the database. Python code can be written for this
import sys
#veritabanı bilgilerini burada alıom
configure= {
'user': 'root',
'password': '19118v#0072.A',
'host': 'localhost',
'database': ' deneme',
}
#veritabanı bağlantısını burada yapıyorum
cnx=mysql.connector.connect(**configure)
#işlemlere devamke
cursor=cnx.cursor()
#var olan kayıtlar için fonksiyon
existing_records=set()
cursor.execute("select ad From kisiler")
for kayit in cursor:
existing_records.add(kayit[0])
#yeni kayıtlar için fonksiyon
with open('/tmp/snmp_value_storage.txt', 'r') as f:
for line in f:
split_line = line.strip().split(',', 1)
oid = split_line[0].strip()
ad_soyad = split_line[1].replace("{", "").replace("}", "") # remove curly braces
# ad_soyad = split_line[1].strip("{}") # remove curly braces
ad, soyad = ad_soyad.split(',') # split by comma
ad = ad.strip() # remove extra whitespace
soyad = soyad.strip() # remove extra whitespace
if ad not in existing_records:
sql = "INSERT INTO kisiler (oid, ad, soyad) VALUES (%s, %s, %s)"
val = (oid, ad, soyad)
cursor.execute(sql, val)
existing_records.add(ad)
#yapılan değişiklikleri kayıet eden fonksiyon
cnx.commit()
#bağlantıyı kapatma
cursor.close()
cnx.close()
Above, we added the data to the database with the help of txt. Now here we will try to save the data sent directly to the database with snmpset. For this, we will update the bash script instead of the script we wrote with python.
#!/bin/bash
PLACE=".1.3.6.1.4.1.1023.1.2.1"
REQ="$2" # Requested OID
DB_USER="root"
DB_PASSWORD="19118v#0072.A"
DB_HOST="localhost"
DB_DATABASE="deneme"
# Function to get value from the database
get_value_from_database() {
OID=$1
mysql -u$DB_USER -p$DB_PASSWORD -h$DB_HOST $DB_DATABASE -N -e \
"SELECT CONCAT(ad, ', ', soyad) FROM kisiler WHERE oid = '$OID';" 2>/dev/null
}
# Function to set value to the value storage
set_value_to_storage() {
OID=$1
VALUE=$2
ad_soyad=$(echo "$VALUE" | tr -d '{}') # remove curly braces
ad=$(echo "$ad_soyad" | cut -d',' -f1) # split by comma
soyad=$(echo "$ad_soyad" | cut -d',' -f2) # split by comma
ad=${ad// /} # remove extra whitespace
soyad=${soyad// /} # remove extra whitespace
mysql -u$DB_USER -p$DB_PASSWORD -h$DB_HOST -D$DB_DATABASE -e \
"INSERT INTO kisiler (oid, ad, soyad) VALUES ('$OID', '$ad', '$soyad');"
}
# Process SET requests by saving the assigned value to the value storage
if [ "$1" = "-s" ]; then
set_value_to_storage $REQ $4
exit 0
fi#
# GETNEXT requests - determine next valid instance
#
if [ "$1" = "-n" ]; then
case "$REQ" in
$PLACE| \
$PLACE.0| \
$PLACE.0.*| \
$PLACE.1) RET=$PLACE.1.0 ;; # netSnmpPassString.0
$PLACE.1.*| \
$PLACE.2| \
$PLACE.2.0| \
$PLACE.2.0.*| \
$PLACE.2.1| \
$PLACE.2.1.0| \
$PLACE.2.1.0.*| \
$PLACE.2.1.1| \
$PLACE.2.1.1.*| \
$PLACE.2.1.2| \
$PLACE.2.1.2.0) RET=$PLACE.2.1.2.1 ;; # netSnmpPassInteger.1
$PLACE.2.1.2.*| \
$PLACE.2.1.3| \
$PLACE.2.1.3.0) RET=$PLACE.2.1.3.1 ;; # netSnmpPassOID.1
$PLACE.2.*| \
$PLACE.3) RET=$PLACE.3.0 ;; # netSnmpPassTimeTicks.0
$PLACE.3.*| \
$PLACE.4) RET=$PLACE.4.0 ;; # netSnmpPassIpAddress.0
$PLACE.4.*| \
$PLACE.5) RET=$PLACE.5.0 ;; # netSnmpPassCounter.0
$PLACE.5.*| \
$PLACE.6) RET=$PLACE.6.0 ;; # netSnmpPassGauge.0
*) exit 0 ;;
esac
else
#
# GET requests - check for valid instance
#
case "$REQ" in
$PLACE.1.0| \
$PLACE.2.1.2.1| \
$PLACE.2.1.3.1| \
$PLACE.3.0| \
$PLACE.4.0| \
$PLACE.5.0| \
$PLACE.6.0) RET=$REQ ;;
*) exit 0 ;;
esac
fi
# Process SET requests by saving the assigned value to the value storage
if [ "$1" = "-s" ]; then
case "$REQ" in
$PLACE.3.0) set_value_to_storage $REQ $4; exit 0 ;;
$PLACE.4.0) set_value_to_storage $REQ $4; exit 0 ;;
*) exit 0 ;;
esac
#
# "Process" GET* requests - return hard-coded value
#
echo "$RET"
case "$RET" in
$PLACE.1.0) echo "string"; echo "ntp status: inactive"; exit 0 ;;
$PLACE.2.1.2.1 ) echo "string"; echo "since Fri 2023-04-07 " exit 0 ;;
$PLACE.2.1.3.1) echo "integer"; echo "0"; exit 0 ;;
$PLACE.3.0) echo "string"; echo "$(get_value_from_database $RET '')"; exit 0 ;;
$PLACE.4.0) echo "string"; echo "$(get_value_from_database $RET '')"; exit 0 ;;
*)
esac