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SNMP Fundamentals

Tutorial2 exercises

What is SNMP?

SNMP (Simple Network Management Protocol) is how you read data from network devices. Your extension asks a device for a value at a specific address — called an OID — and the device responds.

💡 Think of OIDs like database column addresses. You ask for 1.3.6.1.2.1.1.5.0 and get back "SWITCH-01" (the hostname).

OIDs — Object Identifiers

Every piece of data has a dotted-number address. Here are the ones you'll use most:

OID	Name	Returns	Type
`1.3.6.1.2.1.1.5.0`	sysName	Hostname	Scalar
`1.3.6.1.2.1.1.3.0`	sysUpTime	Uptime in ticks	Scalar
`1.3.6.1.2.1.1.1.0`	sysDescr	Device description	Scalar
`1.3.6.1.2.1.2.2.1.2`	ifDescr	Interface names	Table
`1.3.6.1.2.1.31.1.1.1.6`	ifHCInOctets	Bytes in (64-bit)	Table
`1.3.6.1.2.1.31.1.1.1.15`	ifHighSpeed	Speed in Mbps	Table

OIDs under 1.3.6.1.2.1 are standard (work on any device). OIDs under 1.3.6.1.4.1.{vendor} are vendor-specific (need MIB files).

Scalar vs Table — The #1 Rule

This is the most important concept in SNMP extensions. Get it wrong and your extension breaks silently.

Scalar = one value per device. OID ends in .0:

1.3.6.1.2.1.1.5.0  →  sysName = "SWITCH-01"  (one value)

Table = multiple rows (one per interface, CPU, sensor). OID does NOT end in .0:

1.3.6.1.2.1.2.2.1.2  →  ifDescr
  .1 = "GigabitEthernet0/1"
  .2 = "GigabitEthernet0/2"
  .3 = "Vlan100"

table: true → OIDs must NOT end in .0 (GETBULK walk) table: false → OIDs MUST end in .0 (scalar GET) Mix them up = DED016 / DED017 error

🛠 Try it

This extension has 1 bug. The sysUpTime OID is scalar (one value per device) but it's missing .0 at the end. Fix it.

extension.yamlYAML

MIB Files

A MIB maps OID numbers to human-readable names. Standard MIBs ship with ActiveGate. Vendor MIBs go in your extension's snmp/ folder:

extension.zip/
├── extension.yaml
└── snmp/
    └── CISCO-PROCESS-MIB.my   ← vendor MIB

Standard vs Vendor MIBs

MIB	OID Prefix	What It Covers	Bundled?
IF-MIB	`1.3.6.1.2.1.2`	Interfaces (traffic, status)	✓ Yes
SNMPv2-MIB	`1.3.6.1.2.1.1`	System info (name, uptime)	✓ Yes
ENTITY-MIB	`1.3.6.1.2.1.47`	Physical components	✓ Yes
CISCO-PROCESS-MIB	`1.3.6.1.4.1.9.9.109`	Cisco CPU/Memory	✗ Bundle it
CISCO-ENVMON-MIB	`1.3.6.1.4.1.9.9.13`	Cisco temp/fans/PSU	✗ Bundle it

🛠 Try itExercise 2

This interface metric has .0 at the end but it's in a table: true subgroup. Table OIDs should NOT end in .0. Remove it.

extension.yamlYAML

What's Next

In Module 2, you'll turn these OIDs into real metrics with types and metadata.

← PreviousGetting StartedNext →Metrics & Dimensions