I asked:
>
> One of our developers has been playing around with "ndd" and has determined
> that some parameters are not the same on two boxes that should otherwise
> be identical. In particular
>
> tcp_rexmit_interval_min
> tcp_rexmit_interval_initial
>
> with the result that ftp tests to these two machines are producing vastly
> different results in throughput.
>
> We were able to change these settings using ndd as root, but it didn't
> appear to do anything (we're assuming that a reboot would be necessary).
> But I don't like shooting in the dark like this. Can someone point me at
> a good reference, preferrably online so that I can get to it now, on what
> the various settings associated with ndd are, what changing them will do,
> and how I should go about changing the default settings? Thanks much.
The responses:
Everyone told me that a reboot is not necessary. ndd changes are dynamic,
and take effect as soon as you hit the return key. (Of course they do not
affect open connections, but do affect all subsequent changes).
One respondent said that if I'm mucking with these two entries I probably
aught to take a look at tcp_conn_req_max as well.
The great Casper ;^) indicated that having the most recent TCP/IP and
kernel patches are much more necessary, and that "After installing those
patches you should *not* tinker with the default tcp retransmissions
parameters. (Some people still advocate increasing tcp_rexmit_interval_min,
but that really kills performance in the presence of dropped packets)."
Unfortunately in my case both servers are running with the most recent
patches, so it must be something else. He also suggested checking all
startup files for ndd settings installed by a previous rogue sysadmin;
again, no dice.
And finally one kind soul forwarded me the entirety of infodoc 12618, the
"TCP/IP PSD/FAQ" from Sun. Its pretty lengthy, so I won't include it here,
but anyone messing around with the ndd command aught to read this first.
You can get it from Sun's web page (and I can forward it on to anyone who
asks).
Thanks to:
leavitt@webcom.com
Justin Young <justiny@cluster.engr.subr.edu>
Casper Dik <casper@holland.Sun.COM>
"Karl E. Vogel" <vogelke@c17mis.region2.wpafb.af.mil>
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| (312) 347-4901 O---O Now I'm beginning to believe it. |
| http://www.cs.uchicago.edu/~cbarnard --Clarence Darrow |
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