squid-2.6.6 + TSO + windows 98 clients

[Oliver Fromme]

Chuck Swiger wrote:
 > Denis Shaposhnikov wrote:
 > > tcpdump of one of failed requests:
 > > 
 > > 10:35:03.592164 IP 192.168.0.100.1035 > 192.168.0.2.3128: S  
 > > 1423332:1423332(0) win 8192 <mss 536,nop,nop,sackOK>
 > > 10:35:03.592274 IP 192.168.0.2.3128 > 192.168.0.100.1035: S  
 > > 2428819522:2428819522(0) ack 1423333 win 0 <mss 536>
 > 
 > It's interesting that it responds with a zero window size.  That is  
 > typically used by the network stack to indicate extreme congestion  
 > and to have the other side wait for some seconds without sending any  
 > more data.
 > 
 > BTW, why are you using such a small MTU?

576 is Windows' default MTU/MRU for slow PPP (over serial)
connections.  I think it used to be even less for very
slow links (296 bytes, IIRC).  The purpose is to reduce
the amount of data lost when a spike in the telephone line
destroys a packet.  That's especially important when using
analogue equipment (modems) and old telephone lines.

For example, if you have a bad telephone line with an
average of one spike (or other kind of glitch) every 2
seconds, that amounts to 16% packet loss on a 38.4k
connection with 1500 bytes MTU.  With 576 bytes that's
only 6% packet loss, and with 296 bytes it's only 3%.

Best regards
   Oliver

-- 
Oliver Fromme,  secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
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