Filtering Empty Values
Extension metrics model
SNMP devices often return n/a or empty strings for unused interfaces. Filter them out to prevent ghost entities:
dimensions:
- key: if.name
value: oid:1.3.6.1.2.1.31.1.1.1.1
filter: const:$not($eq()) # Exclude empty strings
Filter Expressions
Expression What It Does
────────────────────────────────── ──────────────────────────────
const:$eq(GigabitEthernet) Equals exact string
const:$prefix(Gig) Starts with
const:$suffix(/0/1) Ends with
const:$contains(Ethernet) Contains substring
const:$not($eq()) Not empty
const:$and($prefix(Gig),$not($eq())) Combine: starts with Gig AND not empty
const:$or($prefix(Gig),$prefix(Ten)) Either Gig or Ten interfaces
💡 Use var:ifNameFilter to make filters configurable per monitoring configuration — users can set the filter pattern in the Hub UI.
Variables
Variables make your extension configurable without editing YAML:
vars:
- id: ifNameFilter
displayName: Interface name filter
type: text
description: "Pattern to filter interfaces (e.g., GigabitEthernet)"
- id: ext.activationtag
displayName: Activation tag
type: text
description: "Tag for this monitoring configuration"
🛠 Try it: Add a variable to your extension, then activate it in the Hub — you'll see the variable as a text field in the activation wizard.
Advanced SNMP Properties
Property Default What It Does
──────────────────── ──────── ──────────────────────────────────
Timeout (seconds) 2 Max wait per SNMP query
Retries 3 Retry count on failure
Max repetitions 50 Rows per SNMP GET-BULK request
Max OIDs per query 60 OIDs bundled per request
(F5 BIG-IP: set to 5!)
⚠️ For F5 BIG-IP extensions, set "Max OIDs per query" to 5. The default 60 causes timeouts on F5 devices.