SNMP(V1-2-3)

1- What is SNMP?

SNMP is an application-layer protocol that provides a message format for communication between managers and agents. The SNMP system consists of:

an SNMP manager,
an SNMP agent,
and a MIB.

The SNMP agent contains MIB variables whose values the SNMP manager can request or change. A manager can get a value from an agent or store a value into the agent. The agent gathers data from the MIB, the repository for information about device parameters and network data. The agent can also respond to a manager’s requests to get or set data.

An agent can send unsolicited traps to the manager. Traps are messages alerting the SNMP manager to a condition on the network. Traps can mean improper user authentication, restarts, link status (up or down), MAC address tracking, closing of a TCP connection, loss of connection to a neighbor, or other significant events.

SNMP Versions

Model	Level	Authentication	Encryption	Result
SNMPv1	noAuthNoPriv	Community string	No	Uses a community string match for authentication.
SNMPv2C	noAuthNoPriv	Community string	No	Uses a community string match for authentication.
SNMPv3	noAuthNoPriv	Username	No	Uses a username match for authentication.
SNMPv3	authNoPriv	Message Digest 5 (MD5) or Secure Hash Algorithm (SHA)	No	Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms.
SNMPv3	authPriv (requires the cryptographic software image)	MD5 or SHA	Data Encryption Standard (DES) or Advanced Encryption Standard (AES)	Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. Allows specifying the User-based Security Model (USM) with these encryption algorithms: DES 56-bit encryption in addition to authentication based on the CBC-DES (DES-56) standard. 3DES 168-bit encryption AES 128-bit, 192-bit, or 256-bit encryption

configuring SNMPV2 is so simple, just write :

SW# conf t

SW(conf t)# snmp-server community HRT ro

ro means read only and rw means read/write

configuring SNMPV3 needs three steps:

1- Defining View

SW(conf t)# snmp-server view View_Name iso|family|interface included

iso means everything in MIB.

2- Defining Group

SW(conf t)# snmp-server group Group_Name V3 priv read View_Name

3- Defining User

SW(conf t)# snmp-server user UserName Group_Name v3 auth sha|md5 Password des56/AES Your_Preshared_Key

2- Connect your Device to PRTG

PRTG is really good tool for grabbing information from devices which are working with SNMP. You can download this software and connecting around 100 sensors are free. In other word, you can use it for small business.