What is SNMP?
SNMP -> simple network management protocol
A bit like DHCP. DHCP says “give me that IP, and I’m good to go”
SNMP says “give me that value, and I’m good to go”.
MIBs / OIDs
MIB -> management information base -> all pulled IODs together
OID -> object identifier -> one sensor or one component (one defined thing on that device)
You can actually go to the manufacture site and download the MIB from there. The MIB is the whole book of OIDs for your specific device. But actually you do not need PRTG at all. You could just take the command line and access via SNMP that OID to see what is the bandwidth for example.
Operations (GET,SET,TRAP)
Everytime (for example 60 seconds) you go out there and GET this information, that is called an operation, a GET operation. Here you only need read-only rights.
SET operations are supported as well for SNMP. You could for example shut the interface down with a SET operation because a SET operation is the system actually doing something on that device. Here you need read-write rights.
The TRAP messages come from the device and it’s like an alarm. “Hey something went down here”.
Versions (v1, v2c, v3)
Only Versions v2c and v3 are used nowadays. Version 2 is very common because its simple. Version 2 uses a community-string. But this community-string gets send EVERY GET message in clear text, so the security is not that good.
Version 3 should be the standard but is more complex to set up.
Example
Configuring SNMPv2c and SNMPv3
When creating the user you basically say, this user authenticates with this password (<PASSWORD>) to you, and for the encryption he has this password (<PASSWORD2)
Cisco IOS commands learned in this lesson
| Command | Subcommand | Explanation |
| Snmp-server Community <WORD> | Ro (default) | Enables SNMP with the given community string |
| Rw | Enables SNMP with the given community string as read-write | |
| Snmp-server group <GROUPNAME> v3 | Auth | Setting up snmp v3 with authentication |
| Noauth | Without authentication | |
| Priv | With authentication and encryption | |
| Snmp-server user <USERNAME> <GROUPNAME> v3 auth Sha <PASSWORD> priv aes 128 <PASSWORD2> | create a user for SNMPv3 |