Date: Sat, 18 Oct 2003 14:16:15 -0400 (EDT) From: Carl Mascott <cmascott@att.net> To: vlm@netli.com Cc: freebsd-net@freebsd.org Subject: Re: TCP window size issues Message-ID: <200310181816.h9IIGFjO000362@callisto.local> In-Reply-To: <3F907152.3080706@netli.com>
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Sorry, but you are mistaken, and I can e-mail you the tcpdump
output to prove it.
As I said, I'm running 4.8-R with the PR 11966 patch backed
out. With this kernel, and with any stock FreeBSD 4.6-R or
earlier, the TCP implementation _will_ shrink the receive
window after the connection is established _if_ a routing
table pipesize entry tells it to. See tcp_input.c:tcp_mss()
from 4.6-R or earlier.
The following statements in ppp.conf
set recvpipe 4096
set sendpipe 4096
result in the following default route
route to: default
destination: default
mask: default
gateway: 10.0.0.2
interface: tun0
flags: <UP,GATEWAY,DONE,STATIC,PRCLONING>
recvpipe sendpipe ssthresh rtt,msec rttvar hopcount mtu expire
4096 4096 0 0 0 0 1500 0
This causes tcp_mss() to shrink the receive window after a
connection using the default route is established, as long
as the kernel default recv window size is > 4096 (slight
simplification here).
Lev Walkin wrote:
> Carl Mascott wrote:
> > I have a few TCP window size issues.
> [skip]
> > 3. RFC 793 (TCP) says that shrinking the receive window after
> > connection is established is "strongly discouraged". I'm
> > currently shrinking the receive window on my default route
> > (PPP link) from 32 KB to 4 KB with settings in
> > /etc/ppp/ppp.conf. (Had to back out patch in PR 11966.)
>
> [skip]
>
> > How likely am I to get into trouble by shrinking the TCP
> > receive window? Likely enough that I should make the
>
> RFC793 has nothing to do with the defaults you're setting in ppp.conf.
> RFC merely says that the TCP implementation _itself_ should not shrink
> window after establishing a TCP connection. If the default dictates 4k,
> the TCP implementation will use 4k and will not advertise a much smaller
> window without having accepted that much data.
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