Configuring SNMP v2 on Cisco Devices

Nerd Cafe

Module 1: Lab Setup & Network Diagram

1.1 Required Software & Tools

• GNS3

• PRTG Network Monitor (Installed on 192.168.202.10)

• A simple network topology

1.2 Lab Topology

Lab Topology

Device	Interface	IP Address
Router (R1)	f0/0	192.168.202.1/24
Switch (Sw1)	VLAN 1	192.168.202.2/24
PC1 (VPCS)	e0	192.168.202.11/24
PRTG Server (NMS)	eth1	192.168.202.10/24

The PRTG is running on 192.168.202.10 and will monitor network devices via SNMP v2.

Module 2: Basic Configure

2.1 R1 Router

R1#configure terminal
R1(config)#interface fastEthernet 0/0
R1(config-if)#ip address 192.168.202.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#^Z
R1#write memory

2.2 Sw1 Switch

Sw1#configure terminal
Sw1(config)#interface vlan 1
Sw1(config-if)#ip address 192.168.202.2 255.255.255.0
Sw1(config-if)# no shutdown
Sw1(config-if)#^Z
Sw1#write memory

2.3 PC1

PC1> ip 192.168.202.11/24 192.168.202.1
Checking for duplicate address...
PC1 : 192.168.202.11 255.255.255.0 gateway 192.168.202.1

PC1> show ip

NAME        : PC1[1]
IP/MASK     : 192.168.202.11/24
GATEWAY     : 192.168.202.1
DNS         :
MAC         : 00:50:79:66:68:00
LPORT       : 20008
RHOST:PORT  : 127.0.0.1:20009
MTU         : 1500

PC1> save
Saving startup configuration to startup.vpc
.  done

PC1> ping 192.168.202.1

84 bytes from 192.168.202.1 icmp_seq=1 ttl=255 time=41.697 ms
84 bytes from 192.168.202.1 icmp_seq=2 ttl=255 time=14.898 ms
^C
PC1> ping 192.168.202.2

84 bytes from 192.168.202.2 icmp_seq=1 ttl=255 time=0.338 ms
84 bytes from 192.168.202.2 icmp_seq=2 ttl=255 time=0.443 ms
^C
PC1> ping 192.168.202.10

84 bytes from 192.168.202.10 icmp_seq=1 ttl=128 time=0.574 ms
84 bytes from 192.168.202.10 icmp_seq=2 ttl=128 time=0.769 ms
^C
PC1>

Module 3: Configure SNMP v2 on Cisco Router

Set SNMP Community String (Read-Only Access for PRTG Server 192.168.202.10):

R1(config)#snmp-server community public RO

Define a contact & location:

R1(config)#snmp-server location nerd-cafe-datacenter
R1(config)#snmp-server contact [email protected]

Enable SNMP traps to PRTG Server (192.168.202.10):

R1(config)#snmp-server host 192.168.202.10 version 2c public
R1(config)#snmp-server enable traps

Save the configuration:

R1#write memory
Building configuration...
[OK]
R1#

Module 4: Configure SNMP v2 on Cisco Switch

Set SNMP Community String (Read-Only Access for PRTG Server - 192.168.202.10):

Sw1(config)#snmp-server community public RO

Define a contact & location:

Sw1(config)#snmp-server location nerd-cafe-datacenter
Sw1(config)#snmp-server contact [email protected]

Enable SNMP traps to PRTG Server (192.168.202.10):

Sw1(config)#snmp-server host 192.168.202.10 version 2c public
Sw1(config)#snmp-server enable traps

Save the configuration:

Sw1#write memory
Building configuration...
Compressed configuration from 4630 bytes to 2031 bytes[OK]
Sw1#

Module 5: Install & Configure PRTG Network Monitor (192.168.202.10)

Install PRTG on 192.168.202.10

• Download PRTG Network Monitor from Paessler’s website.

• Install PRTG on 192.168.202.10 (Windows Server/PC).

• After installation, log in to PRTG Web Interface (http://127.0.0.1).

Module 6: Add Cisco Devices to PRTG

6.1 Add Router to PRTG (192.168.202.1)

• Go to Devices → Add Device.

• Enter Router Name: Cisco R1.

• Set IP Address: 192.168.202.1.

• Under Credentials for SNMP Devices, enter:

  • SNMP Version: v2c

  • Community String: public

• Click Save & Continue.

5.2 Add Switch to PRTG (192.168.202.2)

• Go to Devices → Add Device.

• Enter Switch Name: Cisco Sw1.

• Set IP Address: 192.168.202.2.

• Configure SNMP with:

  • SNMP Version: v2c

  • Community String: public

• Click Save & Continue.

Module 7: Monitor Traffic & Alerts

7.1 Add SNMP Sensors

• In PRTG Web Interface, select R1.

• Click Add Sensor → SNMP Traffic.

• Select interfaces to monitor (e.g., FastEthernet0/0).

• Click Add Sensor.

• Repeat the same steps for Sw1 and monitor VLAN 1.

Module 8: Test SNMP Communication

Open VPCS on GNS3 and test network connectivity:

PC1> ping 192.168.202.1

Now, check the traffic of FastEthernet 0/0 of R1:

Module 9: Troubleshooting SNMP Issues

9.1 Check SNMP Status on Cisco Devices

• On Router & Switch:

R1#show snmp
Chassis: 4279256517
Contact: [email protected]
Location: nerd-cafe-datacenter
114 SNMP packets input
    0 Bad SNMP version errors
    0 Unknown community name
    0 Illegal operation for community name supplied
    0 Encoding errors
    182 Number of requested variables
    0 Number of altered variables
    99 Get-request PDUs
    15 Get-next PDUs
    0 Set-request PDUs
    0 Input queue packet drops (Maximum queue size 1000)
115 SNMP packets output
    0 Too big errors (Maximum packet size 1500)
    0 No such name errors
    0 Bad values errors
    0 General errors
    114 Response PDUs
    1 Trap PDUs
SNMP Dispatcher:
   queue 0/75 (current/max), 0 dropped
SNMP Engine:
   queue 0/1000 (current/max), 0 dropped

SNMP logging: enabled
    Logging to 192.168.202.10.162, 0/10, 1 sent, 0 dropped.
R1#

Check if the SNMP community is correctly set:

R1#show running-config | include snmp

9.2 Fixing Common Issues

PRTG cannot discover devices?

• Ensure SNMP is enabled and 192.168.202.10 is allowed as the SNMP host.

No SNMP traffic on PRTG?

• Check firewall settings on PRTG Server (allow UDP port 161 & 162).

Keywords:

SNMP v2, PRTG Network Monitor, Cisco router, Cisco switch, network monitoring, SNMP configuration, network management, NMS, Simple Network Management Protocol, PRTG setup, Cisco SNMP, network performance, network security, SNMP community string, network traffic analysis, fault detection, SNMP traps, Cisco IOS, real-time monitoring, IT infrastructure, مانیتورینگ شبکه