network resources

David Collier-Brown David.Collier-Brown at
Tue Dec 19 15:07:40 GMT 2000

Charles Crawford wrote:
> I'm having problems getting Samba shares to respond quickly enough to not
> time-out on our NT network.
> Once the connection is made, which sometimes takes several login attempts,
> there appear to be no problems. One item worth noting, however, is that
> pinging any of the Linux machines brings a response time 2 times that of the
> Windows machines. 

	Hmmn, that sounds familiar: there is a very old
	slow-start bug in BSD, which was reproduced by
	MS when they added TCP to Windows.

The following is somewhat Solaris-specific, from

This parameter provides the slow-start bug discovered in BSD and
TCP/IP implementations for Solaris. More information on the topic can 
be found on the servers of SUN and in Stevens [6]. To summarize the 
effect, a server starts sending two PDUs at once without waiting for
ACK due to wrong ACK counts. The ACK from connection initiation being 
counted as data ACK - compare with figure 2. Network congestion
algorithms are being undermined. The slow start algorithm does not
the buggy behavior, compare with RFC 2001.

You can also gain performance, if many of your clients are running old 
BSD or derived TCP/IP stacks (like MS). I expect new BSD OS releases 
not to figure this bug, but then I am not familiar with the BSD OS 
family. A reader of this page told me about cutting the latency of 
his server in half, just by using the value of 2.

If you want to know more about this feature and its behavior, you can 
have a look at some experiments 
I have conducted concerning that particular feature. The summary is 
that I agree with the reader: A BSDish client like Windows definitely
profits from using a value of 2.

	We do this as a matter of course with Solaris
	servers with Windows clients: see

	See if Linux has an equivalent to 
	ndd -set /dev/tcp tcp_slow_start_initial 2

	Anyone here aware of the Linux version of this?

David Collier-Brown,  | Always do right. This will gratify some people
185 Ellerslie Ave.,   | and astonish the rest.        -- Mark Twain
Willowdale, Ontario   | //
Work: (905) 415-2849 Home: (416) 223-8968 Email: davecb at

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