I just don't understand how if there is 1 segment that gets lost how this could
translate to such a catastrophic long period of slow-start. How can I minimize t
he impact of the inevitable segment loss/out of order over a WAN. Is QoS the on
ly option?
Are you using TCP offloading on your windows box? I have seen issues
with that in the past where it was dropping data. Turn it off and see
if the issue goes away.
Are other the other connections traversing this path seeing the same
issues?
Still - the only definitive way to solve the problem is by getting
captures from both ends. If you can isolate your wan with taps on each
side and see packets being dropped, you know it's your ATM circuit.
QOS will not help you if you aren't exceeding bandwidth.
Thanks,
Brian Knoll
Senior Network Engineer, TTNET
312-698-6017 desk
312-823-0957 mobile
How exactly are you going to get out-of-order packets over a single
link?
Is there perhaps a firewall somewhere in the communication path? In
that case' it's entirely possible that packets that use certain TCP
options are filtered because the firewall doesn't implement these
options.
For instance, if there are selective acknowledgements, the firewall
may not like that.
Also, if you use the window scale option the firewall probably
doesn't understand that and may easily conclude that a packet which
is in-window with the scale factor applied is out-of-window because
the scale factor _isn't_ applied and drop it, so that you miss the
packet with byte 1, then get the ones with everything upto 65535 and
the rest is dropped, and so many dropped packets will stop TCP dead
in its tracks.
Also note that minimal amounts of cell loss on ATM create huge
amounts of packet loss at the IP layer.
from the phrases used ('catastrophic') my feeling is that perhaps Philip isnt un
derstanding that on a high speed TCP transfer a single missing bit of data can c
ause the whole thing to stop and restart transmission from slow
Steve
Philip Lavine wrote:
I just don't understand how if there is 1 segment that gets lost how this coul
d translate to such a catastrophic long period of slow-start. How can I minimize
the impact of the inevitable segment loss/out of order over a WAN. Is QoS the
only option?
Different tcp congestion control algorithm... Instead of tcp reno use
vegas or westwood?
From: Stephen Wilcox <steve.wilcox@packetrade.com>
To: Philip Lavine <source_route@yahoo.com>
Cc: nanog <nanog@merit.edu>
Sent: Thursday, July 12, 2007 1:09:24 PM
Subject: Re: TCP congestionWell, if its out of order its the same as if its lost or delayed, it needs to
see that missing segment before the window is full
As mentioned you need to get dumps from both ends, you will almost definitely
find that you have packet loss which tripped tcp's slow start mechanism.
Steve
Even if the segment was received out of order what would cause congestion avo
idance to starve the connection of legitimate traffic for 15 to 20 seconds? That
is the core of the problem.
Come on folks, don't be afraid. We all know the beast is to blame for
this, just don't say the name three times...
Shub Internet
Philip Lavine wrote:
I just don't understand how if there is 1 segment that gets lost how this coul
d translate to such a catastrophic long period of slow-start. How can I minimize
the impact of the inevitable segment loss/out of order over a WAN. Is QoS the
only option?
From: Stephen Wilcox <steve.wilcox@packetrade.com>
To: Philip Lavine <source_route@yahoo.com>
Cc: nanog <nanog@merit.edu>
Sent: Thursday, July 12, 2007 1:09:24 PM
Subject: Re: TCP congestionWell, if its out of order its the same as if its lost or delayed, it needs to
see that missing segment before the window is full
As mentioned you need to get dumps from both ends, you will almost definitely
find that you have packet loss which tripped tcp's slow start mechanism.
Steve
Even if the segment was received out of order what would cause congestion avo
idance to starve the connection of legitimate traffic for 15 to 20 seconds? That
is the core of the problem.
Iljitsch van Beijnum wrote:
How exactly are you going to get out-of-order packets over a single link?
There is a once popular router that has been known to do that in some
configurations due to multiple paths within the device.
- Kevin