Advanced OS X users know that Darwin comes with ipfw, which can be used to set up a custom firewall. This same service however can be used to also limit bandwidth on specific ports.
Example:
sudo ipfw pipe 1 config bw 15KByte/s
creates a pipe that only allows up to 15KB/s to go through.
sudo ipfw add 1 pipe 1 src-port 80
will attach that pipe to the outgoing traffic on port 80, effectively limiting the outgoing traffic of the web server.
sudo ipfw delete 1
will remove the pipe from the port.
Mac OS X Hints
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