- OpenTTD's default settings for maximum number of clients, and amount of data

   from clients to process are chosen to not influence the normal playing of

   people, but to prevent or at least make it less likely that someone can

   perform a (distributed) denial-of-service attack on your server by causing

   an out-of-memory event by flooding the server with data to send to all

   clients. The major factor in this is the maximum number of clients; with

   32 clients "only" sending one chat message causes 1024 messages to be

   distributed in total, with 64 clients that already quadruples to 4096. Given

   that upstream bandwidth is usually the limiting factor, a queue of packets

   that need to be sent will be created.

   To prevent clients from exploiting this "explosion" of packets to send we

   limit the number of incoming data, resulting in effectively limiting the

   amount of data that OpenTTD will send to the clients. Even with the default

   limits it is possible to generate about 70.000 packets per second, or about

   7 megabit per second of traffic.

   Given that OpenTTD kicks clients after they have not reacted within about 9

   seconds from sending a frame update packet it would be possible that OpenTTD

   keeps about 600.000 packets in memory, using about 50 megabytes of memory.

   Given that OpenTTD allows short bursts of packets, you can have slightly

   more packets in memory in case of a distributed denial of service attack.

   When increasing the amount of incoming data, or the maximum number of

   clients the amount of memory OpenTTD needs in case of a distributed denial

   of service attack is linearly related to the amount of incoming data and

   quadratic to the amount of clients. In short, a rule of thumb for, the

   maximum memory usage for packets is:

       #max_clients * #max_clients * bytes_per_frame * 10 KiB.