liminfoSNMP Reference
Free reference guide: SNMP Reference
About SNMP Reference
The SNMP Reference is a searchable cheat sheet covering the Simple Network Management Protocol used for monitoring and managing network devices. It documents GET, GET-NEXT, SET, WALK, and BULK GET operations with practical snmpget, snmpwalk, and snmpbulkget command examples for querying routers, switches, firewalls, and servers.
The OID section covers the hierarchical Object Identifier structure including system group OIDs (sysDescr, sysUpTime, sysName, sysLocation), interfaces group OIDs (ifNumber, ifDescr, ifSpeed, ifInOctets/ifOutOctets), and enterprise OIDs for Cisco, Juniper, Net-SNMP, and HP. MIB file loading, installation paths, and snmptranslate usage for browsing MIB trees are also covered.
Security sections detail community string configuration for SNMPv1/v2c on both Cisco devices and Linux Net-SNMP agents, SNMPv3 user creation with SHA/AES authentication and encryption, security levels (noAuthNoPriv, authNoPriv, authPriv), and group/view access control. Trap and Inform setup includes snmptrapd daemon configuration, standard trap types (coldStart, linkDown, linkUp), and test trap transmission.
Key Features
- SNMP operations: GET, GET-NEXT, SET, WALK, BULK GET with Net-SNMP command examples
- OID hierarchy reference: system group, interfaces group, and vendor enterprise OIDs
- MIB file management: installation paths, loading custom MIBs, and snmptranslate browsing
- Community string configuration for Cisco IOS and Linux Net-SNMP (snmpd.conf)
- SNMPv3 security: user creation, SHA/AES authentication/encryption, and security levels
- SNMPv3 group and view access control for Cisco and Net-SNMP agents
- Trap and Inform setup: snmptrapd configuration, standard trap types, and test transmission
- Searchable by category with dark mode support on desktop, tablet, and mobile
Frequently Asked Questions
What is SNMP and how does it work?
SNMP (Simple Network Management Protocol) is a protocol for monitoring and managing network devices. It uses a Manager (NMS) and Agent architecture where the manager queries agents on devices via UDP port 161 for status data, and agents send asynchronous notifications (traps) to the manager on UDP port 162.
What is the difference between SNMP GET, WALK, and BULK GET?
GET retrieves a single specific OID value, GET-NEXT retrieves the next OID in the MIB tree (used for sequential traversal), WALK performs repeated GET-NEXT operations to traverse an entire subtree, and BULK GET (v2c/v3 only) efficiently retrieves multiple OID values in a single request with configurable non-repeaters and max-repetitions.
How do I read common system information via SNMP?
Query the system group OIDs: sysDescr (.1.3.6.1.2.1.1.1) for system description, sysUpTime (.1.3.6.1.2.1.1.3) for uptime, sysName (.1.3.6.1.2.1.1.5) for hostname, and sysLocation (.1.3.6.1.2.1.1.6) for location. For example: snmpget -v2c -c public 192.168.1.1 sysName.0
What is the difference between SNMPv2c and SNMPv3?
SNMPv2c uses community strings (essentially passwords sent in plaintext) for authentication. SNMPv3 adds proper security with three levels: noAuthNoPriv (username only), authNoPriv (authentication with MD5/SHA), and authPriv (authentication plus encryption with DES/AES), making it suitable for secure environments.
How do I configure SNMPv3 users?
On Linux Net-SNMP, use net-snmp-create-v3-user with -a SHA -x AES flags for authentication and encryption. On Cisco devices, use "snmp-server user myuser mygroup v3 auth sha authPass priv aes 128 privPass". Then query with: snmpwalk -v3 -l authPriv -u myuser -a SHA -A authPass -x AES -X privPass host system
What are SNMP traps and informs?
Traps are asynchronous notifications sent from agents to the SNMP manager when events occur (coldStart, warmStart, linkDown, linkUp, authenticationFailure). Informs are similar but include an acknowledgement mechanism where the agent waits for an ACK response, providing higher reliability than standard traps.
How do I set up SNMP trap reception?
Configure snmptrapd with /etc/snmp/snmptrapd.conf (set "authCommunity log,execute,net public"), then run "snmptrapd -Lo -f" to start the daemon. On Cisco, configure "snmp-server host 192.168.1.100 version 2c public" and "snmp-server enable traps" to send traps to the manager.
Is this SNMP reference free to use?
Yes, this SNMP Reference is completely free with no account required. All content is browsable in your browser with zero server processing. It is part of liminfo.com's collection of free networking and infrastructure reference tools.