Accidentally announced a /24 to my upstream, survived

So how to say... I am new to this. I have the /24 from my university. I wanted to announce it at my apartment. I put the prefix in my router, clicked apply, and did not notice the upstream session was still active. The full /24 went to my residential provider. I only realized when my phone started ringing.

The provider called me. Very calm. «Why do you have 256 addresses at a residential line?» I did not know what to say. I said yes, I made a mistake. They filtered it after 12 minutes. No bill, no termination. I was lucky only.

Is this common? How do people prevent this?

Dear, you must kindly configure prefix filters on your own equipment before establishing any BGP session. This is the basic responsibility of the network administrator itself. Your upstream provider should also have ingress filtering applied, but you cannot rely on their protection only.

Please use a tool such as IRR to validate your intended announcements. Many providers offer this service at cheap rates only. You may also request that your upstream set a maximum prefix limit as a safeguard.

I am glad that your provider was understanding. Others would terminate service immediately for such a leak.

12 minutes? That's a long leak for residential.