When spoofing NDP router advertisements, the router lifetime is always 1800s (30min). When spoofing is stopped, the targets keep the route for the remaining time. Depending on the setup, the targets could loose connectivity until the route expires.

Since router advertisements get sent every second, a shorter lifetime is sufficient and allows the targets to recover more quickly. My suggestion is changing it to 10 seconds or something similar.

Alternatively, the router lifetime could be made configurable using an option ndp.spoof.router_lifetime. I already implemented such an option (konradh@ad36a8e) and would like to contribute it to this project.