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Linux - Tuning TCP di Linux 2.4 system
Oleh : Adhytia Wisnu Sasmita
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Tulisan ini kiriman dari Mas Adhytia Wisnu Sasmita, praktisi IT Surabaya.
Mohon maaf penulis belum berkesempatan untuk menterjemah tulisan ini kedalam
bahasa indonesia.

Enabling and disabling some of the advanced features of TCP:
(Usually it is a good idea for these to be enabled)
        /proc/sys/net/ipv4/tcp_timestamps
        /proc/sys/net/ipv4/tcp_window_scaling
        /proc/sys/net/ipv4/tcp_sack
To enable all these features, for example, do the following as root:

        echo 1 > /proc/sys/net/ipv4/tcp_timestamps
        echo 1 > /proc/sys/net/ipv4/tcp_window_scaling
        echo 1 > /proc/sys/net/ipv4/tcp_sack

Path MTU discovery can be enabled and disabled using the following boolean
sysctl variable:

        /proc/sys/net/ipv4/ip_no_pmtu_disc
But be on the lookout for blackholes if this is enabled, as indicated at the
beginning of the document. Please see the following URL for additional
documentation on sysctl variables:

http://www.linuxhq.com/kernel/v2.4/doc/networking/ip-sysctl.txt.html
   
Tuning the default and maximum window sizes:

        /proc/sys/net/core/rmem_default   - default receive window
        /proc/sys/net/core/rmem_max       - maximum receive window
        /proc/sys/net/core/wmem_default   - default send window
        /proc/sys/net/core/wmem_max       - maximum send window

        /proc/sys/net/ipv4/tcp_rmem       - memory reserved for TCP rcv buffers
        /proc/sys/net/ipv4/tcp_wmem       - memory reserved for TCP snd buffers
The following values would be reasonable for path with a large BDP:


        echo 8388608 > /proc/sys/net/core/wmem_max
        echo 8388608 > /proc/sys/net/core/rmem_max
        echo "4096 87380 4194304" > /proc/sys/net/ipv4/tcp_rmem
        echo "4096 65536 4194304" > /proc/sys/net/ipv4/tcp_wmem

You will find a short description in
LINUX-SOURCE_DIR/Documentation/networking/ip-sysctl.txt

If you would like these changes to be preserved across reboots, it may be a good
idea to add these commands to your /etc/rc.d/rc.local file.


Linux users may want to look into the Web100 project. In addition to providing
complete instrumentation of the TCP stack, it has features for doing auto tuning
of send and receive buffers.

For paths with a very large BDP, it also has some features that will allow you
to get better transfers.

User testimonial: With the tuned TCP stacks it was possible to get a maximum
throughput between 1.5 - 1.8 Mbit/s via a 2Mbit/s satellite link,
measured with netperf.

--
Best Regards,
Adhytia Wisnu Sasmita                          
FreeBSD Hosting, Plesk Controller, Web Development, Multimedia Production
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