net.inet.tcp.rexmit_min (default 3 ticks equiv)
This sysctl is the retransmit timer RTO minimum,
specified in milliseconds. This value is
designed for algorithmic stability only.
net.inet.tcp.rexmit_slop (default 200ms)
This sysctl is the retransmit timer RTO slop
which is added to every retransmit timeout and
is designed to handle protocol stack overheads
and delayed ack issues.
Note that the *original* code applied a 1-second
RTO minimum but never applied real slop to the RTO
calculation, so any RTO calculation over one second
would have no slop and thus not account for
protocol stack overheads (TCP timestamps are not
a measure of protocol turnaround!). Essentially,
the original code made the RTO calculation almost
completely irrelevant.
Please note that the 200ms slop is debateable.
This commit is not meant to be a line in the sand,
and if the community winds up deciding that increasing
it is the correct solution then it's easy to do.
Note that larger values will destroy performance
on lossy networks while smaller values may result in
a greater number of unnecessary retransmits.
o Add a mutex (sb_mtx) to struct sockbuf. This protects the data in a
socket buffer. The mutex in the receive buffer also protects the data
in struct socket.
o Determine the lock strategy for each members in struct socket.
o Lock down the following members:
- so_count
- so_options
- so_linger
- so_state
o Remove *_locked() socket APIs. Make the following socket APIs
touching the members above now require a locked socket:
- sodisconnect()
- soisconnected()
- soisconnecting()
- soisdisconnected()
- soisdisconnecting()
- sofree()
- soref()
- sorele()
- sorwakeup()
- sotryfree()
- sowakeup()
- sowwakeup()
Reviewed by: alfred
In order to ensure security and functionality, RFC 1948 style
initial sequence number generation has been implemented. Barring
any major crypographic breakthroughs, this algorithm should be
unbreakable. In addition, the problems with TIME_WAIT recycling
which affect our currently used algorithm are not present.
Reviewed by: jesper
generation scheme. Users may now select between the currently used
OpenBSD algorithm and the older random positive increment method.
While the OpenBSD algorithm is more secure, it also breaks TIME_WAIT
handling; this is causing trouble for an increasing number of folks.
To switch between generation schemes, one sets the sysctl
net.inet.tcp.tcp_seq_genscheme. 0 = random positive increments,
1 = the OpenBSD algorithm. 1 is still the default.
Once a secure _and_ compatible algorithm is implemented, this sysctl
will be removed.
Reviewed by: jlemon
Tested by: numerous subscribers of -net
connection. The information contained in a tcptemp can be
reconstructed from a tcpcb when needed.
Previously, tcp templates required the allocation of one
mbuf per connection. On large systems, this change should
free up a large number of mbufs.
Reviewed by: bmilekic, jlemon, ru
MFC after: 2 weeks
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.
PR: kern/1689
Submitted by: jesper
Reviewed by: wollman
MFC after: 2 weeks
but have a network interrupt arrive and deactivate the timeout before
the callout routine runs. Check for this case in the callout routine;
it should only run if the callout is active and not on the wheel.
better recovery for multiple packet losses in a single window.
The algorithm can be toggled via the sysctl net.inet.tcp.newreno,
which defaults to "on".
Submitted by: Jayanth Vijayaraghavan <jayanth@yahoo-inc.com>
- eliminate the fast/slow timeout lists for TCP and instead use a
callout entry for each timer.
- increase the TCP timer granularity to HZ
- implement "bad retransmit" recovery, as presented in
"On Estimating End-to-End Network Path Properties", by Allman and Paxson.
Submitted by: jlemon, wollmann
is believed to have been broken with the Brakmo/Peterson srtt
calculation changes. The result of this bug is that TCP connections
could time out extremely quickly (in 12 seconds).
Also backed out jdp's partial fix for this problem in rev 1.17 of
tcp_timer.c as it is obsoleted by this commit.
Bug was pointed out by Kevin Lehey <kml@roller.nas.nasa.gov>.
PR: 6068
This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
time, in seconds, that state for non-established TCP sessions stays about)
a sysctl modifyable variable.
[part 1 of two commits, I just realized I can't play with the indices as
I was typing this commit message.]
pr_usrreq mechanism which was poorly designed and error-prone. This
commit renames pr_usrreq to pr_ousrreq so that old code which depended on it
would break in an obvious manner. This commit also implements the new
interface for TCP, although the old function is left as an example
(#ifdef'ed out). This commit ALSO fixes a longstanding bug in the
TCP timer processing (introduced by davidg on 1995/04/12) which caused
timer processing on a TCB to always stop after a single timer had
expired (because it misinterpreted the return value from tcp_usrreq()
to indicate that the TCB had been deleted). Finally, some code
related to polling has been deleted from if.c because it is not
relevant t -current and doesn't look at all like my current code.
circumstances, caused perfectly good connections to be dropped. This
happened for connections over a LAN, where the retransmit timer
calculation TCP_REXMTVAL(tp) returned 0. If sending was blocked by flow
control for long enough, the old code dropped the connection, even
though timely replies were being received for all window probes.
Reviewed by: W. Richard Stevens <rstevens@noao.edu>
1) Set the persist timer to help time-out connections in the CLOSING state.
2) Honor the keep-alive timer in the CLOSING state.
This fixes problems with connections getting "stuck" due to incompletion
of the final connection shutdown which can be a BIG problem on busy WWW
servers.
keepalive on all tcp sessions. Setsockopt(2) cannot override this setting.
Maybe another one is needed that just changes the default for SO_KEEPALIVE ?
Requested by: Joe Greco <jgreco@brasil.moneng.mei.com>
