CCNA – SNMP Questions
Note: If you are not sure about SNMP, please read our SNMP tutorial.
SNMP is an application-layer protocol that provides a message format for communication between SNMP managers and agents. SNMP provides a standardized framework and a common language used for the monitoring and management of devices in a network.
The SNMP framework has three parts:
+ An SNMP manager
+ An SNMP agent
+ A Management Information Base (MIB)
The SNMP manager is the system used to control and monitor the activities of network hosts using SNMP. The most common managing system is called a Network Management System (NMS). The term NMS can be applied to either a dedicated device used for network management, or the applications used on such a device. A variety of network management applications are available for use with SNMP. These features range from simple command-line applications to feature-rich graphical user interfaces (such as the CiscoWorks2000 line of products).
The SNMP agent is the software component within the managed device that maintains the data for the device and reports these data, as needed, to managing systems. The agent and MIB reside on the routing device (router, access server, or switch). To enable the SNMP agent on a Cisco routing device, you must define the relationship between the manager and the agent.
The Management Information Base (MIB) is a virtual information storage area for network management information, which consists of collections of managed objects.
Sometimes, messages like this might appear in the router console:
%SNMP-3-CPUHOG: Processing [chars] of [chars]
They mean that the SNMP agent on the device has taken too much time to process a request.
You can determine the cause of high CPU use in a router by using the output of the show process cpu command.
Note: A managed device is a part of the network that requires some form of monitoring and management (routers, switches, servers, workstations, printers…).
A TRAP is a SNMP message sent from one application to another (which is typically on a remote host). Their purpose is merely to notify the other application that something has happened, has been noticed, etc. The big problem with TRAPs is that they’re unacknowledged so you don’t actually know if the remote application received your oh-so-important message to it. SNMPv2 PDUs fixed this by introducing the notion of an INFORM, which is nothing more than an acknowledged TRAP.
Cisco IOS software supports the following versions of SNMP:
+ SNMPv1 – The Simple Network Management Protocol: A Full Internet Standard, defined in RFC 1157. (RFC 1157 replaces the earlier versions that were published as RFC 1067 and RFC 1098.) Security is based on community strings.
+ SNMPv2c – The community-string based Administrative Framework for SNMPv2. SNMPv2c (the “c” stands for “community”) is an Experimental Internet Protocol defined in RFC 1901, RFC 1905, and RFC 1906. SNMPv2c is an update of the protocol operations and data types of SNMPv2p (SNMPv2 Classic), and uses the community-based security model of SNMPv1.
+ SNMPv3 – Version 3 of SNMP. SNMPv3 is an interoperable standards-based protocol defined in RFCs 2273 to 2275. SNMPv3 provides secure access to devices by a combination of authenticating and encrypting packets over the network. The security features provided in SNMPv3 are as follows:
– Message integrity: Ensuring that a packet has not been tampered with in transit.
– Authentication: Determining that the message is from a valid source.
– Encryption: Scrambling the contents of a packet prevent it from being learned by an unauthorized source.
SNMPv1/v2 can neither authenticate the source of a management message nor provide encryption. Without authentication, it is possible for nonauthorized users to exercise SNMP network management functions. It is also possible for nonauthorized users to eavesdrop on management information as it passes from managed systems to the management system. Because of these deficiencies, many SNMPv1/v2 implementations are limited to simply a read-only capability, reducing their utility to that of a network monitor; no network control applications can be supported. To correct the security deficiencies of SNMPv1/v2, SNMPv3 was issued as a set of Proposed Standards in January 1998. -> A is correct.
The two additional messages are added in SNMP2 (compared to SNMPv1)
GetBulkRequest The GetBulkRequest message enables an SNMP manager to access large chunks of data. GetBulkRequest allows an agent to respond with as much information as will fit in the response PDU. Agents that cannot provide values for all variables in a list will send partial information. -> E is correct.
InformRequest The InformRequest message allows NMS stations to share trap information. (Traps are issued by SNMP agents when a device change occurs.) InformRequest messages are generally used between NMS stations, not between NMS stations and agents. -> C is correct.
Note: These two messages are carried over SNMPv3.