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TheLostOne
Asked: 2012-03-23 10:49:04 +0800 CST

Why isn't ipfw correctly limiting the bandwidth?

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I've played around with the ipfw command on a Mac and tried to limit the bandwidth to 1MBit/s.

sudo ipfw add pipe 1 ip from any to me
sudo ipfw pipe 1 config bw 1MBit/s

These are the statements I'm using. ipfw indeed limits the bandwidth drastically but according to speedtest.net only to ~7.7 Mbps on a 100 Mbps line. With a restriction to 3MBit/s the effective download is ~23.13 Mbps. Apparently the ipfw always uses a factor ~7.7 of the given limit. With a limit of 4 Mbps the effective speed is ~30,84 Mbps, with 8 Mbps it's ~61.6 Mbps and so on...

Anyone knows why this is the reason? Is it a bug or do I use the statement wrong?

Thank you

ipfw bandwidth-control osx-lion

1 Answers

  1. Best Answer

    Seems like your IPFW treat bw xMBits as xMBytes by first significant letters in the units :) Just lowercase to xMbits and probably you'll get what you want.

    man ipfw

    bw bandwidth | device
             Bandwidth, measured in [K|M]{bit/s|Byte/s}.
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