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File transfer speeds and NAT loopback

Discussion in 'Asuswrt-Merlin' started by evalf, Jul 17, 2019.

  1. evalf

    evalf Occasional Visitor

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    I'm running an SFTP server on one of my computers, connected via ethernet to my RT-AC68U running the latest Merlin firmware.

    When I access the server directly using its internal IP address from another computer connected to Wifi I'm getting on average 44MB/s download speed. I have made the server accessible to the outside with the relevant port forwarding. If I access it using the router's external address ****.asuscomm.com from inside the network I'm getting 24MB/s download speed, just over half of what I'm getting using the direct IP.

    I was initially concerned that when accessing via the asuscomm address the traffic would somehow transit outside the network, but after checking the traffic monitor it is not the case, the WAN connection stays roughly at zero during the transfer.

    Is there some way to improve the transfer speeds when accessing the server via the asuscomm address, or is it just the case that the NAT loopback does restrict the transfer speeds? Thanks for your advice.
     
  2. ColinTaylor

    ColinTaylor Part of the Furniture

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    NAT loopback can't use hardware acceleration because it is being routed through the router's CPU. So 24MB/s (192Mb/s) sounds like it's in the right ballpark for one of the older (slower) RT-AC68U's.

    What CPU Frequency do you have reported on the Tools page of the router?
     
  3. evalf

    evalf Occasional Visitor

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    Thanks for your reply. The CPU frequency is 800 MHz. I just had a look at the CPU usage when doing the transfer via the NAT loopback and indeed it is close to 100%, and much lower when using the local IP.
     
  4. ColinTaylor

    ColinTaylor Part of the Furniture

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    OK, that's the expected throughput then. I was getting those kind of speeds with my AC68U, also at 800MHz. That is why I've overclocked it to 1200MHz so I can get > 220Mbps.