On Fri, Oct 12, 2012 at 9:13 AM, John Baldwin <j...@freebsd.org> wrote: > Back in 2001 FreeBSD added a hack to strip TCP options from retransmitted SYNs > starting with the 3rd SYN in this block in tcp_timer.c: > > /* > * Disable rfc1323 if we haven't got any response to > * our third SYN to work-around some broken terminal servers > * (most of which have hopefully been retired) that have bad VJ > * header compression code which trashes TCP segments containing > * unknown-to-them TCP options. > */ > if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3)) > tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP); > > There is even a PR for the original bug report: kern/1689 > > [..snip..] > > The original motivation of this change is to work around broken terminal > servers that were old when this change was added in 2001. Over 10 years later > I think we should at least have an option to turn this work-around off, and > possibly disable it by default. > > Thoughts? > > -- > John Baldwin
Not that it alone merits keeping the code in, but there are some cases where this comes in handy. I ran into an issue with heavily trafficked Linux <-> FBSD boxes here - http://lists.freebsd.org/pipermail/freebsd-net/2012-March/031881.html. Linux would deny the connection because in FBSD ithe n and outbound timestamp randomization isn't sync'd to the same base, so when FBSD would hit a 2MSL connection Linux would simply ignore the SYN. After the 3rd SYN FBSD would drop support, and Linux would finally honor the request. I doubt this is too widespread, but it would probably break things for a few folks. Jason _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
