I wonder if an inexpensive and credible test of the acceptability of
(URG(0) && urgent pointer > 0) by middle boxes might be possible using
load-testing/reachability services like NeoLoad or Pingdom?
On 2019-12-01 11:35 a.m., Sebastian Moeller wrote:
Hi Jonathan,
On Nov 30, 2019, at 23:23, Jonathan Morton <[email protected]> wrote:
On 1 Dec, 2019, at 12:17 am, Carsten Bormann <[email protected]> wrote:
There are unfortunate problems with introducing new TCP options, in that some
overzealous firewalls block traffic which uses them. This would be a
deployment hazard for SCE, which merely using a spare header flag avoids. So
instead we are still planning to use the spare bit - which happens to be one
that AccECN also uses, but AccECN negotiates in such a way that SCE can safely
use it even with an AccECN capable partner.
This got me curious: Do you have any evidence that firewalls are friendlier to
new flags than to new options?
This influenced the design of AccECN as well; in an early version it would have
used only a TCP option and left the TCP flags alone. When it was found that
firewalls would often interfere with this, the three-bit field in the TCP flags
area was cooked up.
Belt and suspenders, eh? But realistically, the idea of using an
accumulating SCE counter to allow for a lossy reverse ACK path seems sort of
okay (after all TCP relies on the same, so there would be a nice symmetry ).
I really wonder whether SCE could not, in addition to its current bit, borrow the URG
pointer field in cases when it is not used, or not fully used (if the MSS is smaller
than 64K there might be a few bits leftover, with an MTU < 2000 I would expect
that ~5 bits might still be usable in that rate case). I might be completely of to
lunch here, but boy a nice rarely used contiguous 16bit field in the TCP header, what
kind of mischief one could arrange with that ;) Looking at the AccECN draft, I see
that my idea is not terribly original... But, hey for SCE having an additional higher
fidelity SCE counter might be a nice addition, assuming URG(0), urgent pointer > 0
will not bleached/rejected by uninitiated TCP stacks/middleboxes...
Indeed, do we know if this was what the studies used, that Mirja
Kuhlewind referred to?
--dave
--
David Collier-Brown, | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
[email protected] | -- Mark Twain
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