Why are my scans so slow when I enable SNMP?

Most devices only require a single query to obtain all of their SNMP information. Unfortunately, Cisco Catalyst devices have per-VLAN SNMP. That is, they present each VLAN ID as a different SNMP community (community@ID) or SNMPv3 context, and only return results for the current VLAN when queried.

runZero detects this, enumerates all of the VLANs, and then performs a normal single-pass SNMP scan once per VLAN to get all of the information.

Some customers set up hundreds of VLANs per switch, so the scan takes a long time, and uses switch resources. There’s no real fix for this, other than to have runZero skip fetching SNMP information from the switch.