Slow Home LAN

Hello all,

I have a very slow internal LAN. Meaning when I copy files between machines, I get about 7MBps/56Mbps. I should be all gigabit compliant and have verified this using iperf between all machines, and I get at least 900Mbps between all machines using iperf. However something happens at the protocol layer and I'm not sure how to debug and fix this, and would appreciate some help if I could. Also individual machines accessing the Internet seems be really good too, i.e. 20MBps during off-peak times (cable modem being the bottleneck, as it should be). Internally machine-to-machine is not good. I'm using scp and Windows copy to determine the speeds.

Some details on my home LAN:

• Cable modem internet comes into Debian server running testing distro
  • two NIC's, first is for Internet from cable modem, second NIC is for LAN
  • shorewall firewall protection, mail server, squid proxy, bind nameserver
• All user machines are Win7 Pro 64-bit
• Devices are connected using an TP-Link gigabit switch
  • Also tried using a Netgear gigabit switch to rule that out as a problem
• All Ethernet cables are CAT-6 or CAT-5e, recently replaced to rule this out as a problem (Monoprice)
• Checked all NIC settings to confirm full duplex/gigabit is enabled
  • Would assume that iperf would not see 900Mbps+ if this wasn't the case

So copying files between any two machines is slow, i.e. about 7MBps and I expect something closer to 100MBps to reflect what I see based on the results with iperf testing. Any suggestions on how to troubleshoot and fix this would be very helpful. Thanks a lot!