Awful Network Performance I have a MacBook pro running Mountain Lion. When I copy files over the local network, I get around 200Kb/s on a 1Gbps link (the light on the switch indicates 1Gbps). This morning I went to download the XCode 5 DP6 and was pretty apalled by 50Kb/s. Downloading from a Windows 8 machine connected to the same switch yields 2.2Mb/s.

I've tried running the following, but is there anything else I could try?

sudo sysctl -w net.inet.tcp.delayed_ack=0
Several things:

Do a TCP Dump to analyze traffic, to see if you're machine is hitting sites that are bogging it down. At the command line, type sudo tcpdump -i en1

Do a DNS cache reset. At the command line, type sudo dscacheutil -flushcache

Check the MTU settings. Confirm with your ISP what the MTU setting should be, and then go to System Preferences -&gt; Network. Find your connection and click Advanced. Find the Hardware tab, and enter the MTU setting manually if it does not match.