Cisco WS-C2980G-A Software Guide - Page 372

Understanding How SNMP Works Chapter 24 Configuring SNMP Security Models and Levels A security model is an authentication strategy that is set up for a user and the group in which the user resides. A security level is the permitted level of security within a security model. A combination of a security model and a security level will determine which security mechanism is employed when handling an SNMP packet. Three security models are available: SNMPv1, SNMPv2c, and SNMPv3. Table 24-2 identifies what the combinations of security models and levels mean. Table 24-2 Security Model Combinations Model Level Authentication Encryption What Happens v1 noAuthNoPriv Community No String Uses a community string match for authentication. v2c noAuthNoPriv Community No String Uses a community string match for authentication. v3 noAuthNoPriv Username No Uses a username match for authentication. v3 authNoPriv MD5 or SHA No Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. v3 authPriv MD5 or SHA DES Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. Provides DES 56-bit encryption in addition to authentication based on the CBC-DES (DES-56) standard. Note the following about SNMPv3 objects: • Each user belongs to a group. • A group defines the access policy for a set of users. • SNMP objects refer to an access policy for reading, writing, and creating. • A group determines the list of notifications its users can receive. • A group also defines the security model and security level for its users. SNMP ifindex Persistence Feature The SNMP ifIndex persistence feature is always enabled. With the ifIndex persistence feature, the ifIndex value of the port and VLAN is always retained and used after the following occurrences: • Switch reboot • High-availability switchover • Software upgrade • Module reset • Module removal and insertion of the same type of module For Fast EtherChannel and Gigabit EtherChannel interfaces, the ifIndex value is only retained and used after a high-availability switchover. 24-4 Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide-Release 8.1 78-15486-01