[baldfat]

To my understanding to take down an IRC server doesn't even need to be a DDOS (Distrubuted Denial of Service) AKA multiple of computers and connections. One good DoS (Denial of Service) AKA one computer one connection, is all it takes to take it down.

[pixl97]

Those are easy to block with a firewall policy. DDOS is the only way to sustain an attack.

[forgottenpass]

It's a matter of bandwidth. If a single malicious actor can clog the the IRC server's uplink on the internet facing side of their firewall yes, otherwise no.

[anaphor]

It's probably the case that lots of people try that, but unless the IRC server(s) are being hosted on their home network then I doubt one or two computers could bring a whole IRC network down.