Scanning routers

How do I run runZero without crashing my router?

A router that crashes mid-scan is usually a stateful router that ran out of session slots. Any of these changes can help:

• Deploy additional Explorers so you aren’t scanning across routed networks (wired and WiFi, multiple VLANs, and so on).
• Reduce the Max group size in your scan configuration. This caps how many targets runZero scans at once, which corresponds to the number of connections the router sees. The default is 4096.
• Reduce the scan speed. Failed connections then have more time to expire before runZero attempts new ones.
• If the router can run in bridge mode and you don’t need its NAT features, bridge mode is likely more reliable. For example, if an ISP-provided router is connected to a WiFi mesh system, you’ll likely want to run the mesh system in bridge mode and let the ISP router handle all routing, including NAT. You should then be able to scan across your WiFi network without crashing the base stations.

A stateful router tracks every connection passing through it, and a scan opens thousands of connections in a short burst. The crash usually happens when the router is doing Network Address Translation (NAT) or acting as a stateful security firewall.