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RB1100 bandwidth test over L2TP link - problems

Posted: Mon Jun 14, 2010 1:08 pm
by NAB
Hi,

I have a RB1100 (ROS 4.10) with several ROS clients (ROS 5.0b2, ROS 4.5, ROS 4.10) connected over unencrypted L2TP links.

When I run a bandwidth test on the RB1100 against one of the clients (any one of them), UDP works absolutely fine, but using TCP causes all sorts of problems....

1 - The CPU on the RB1100 jumps to 100%
2 - The RB1100 becomes very slow to respond on all ethernet interfaces (not just the one the L2TP tunnel is running on) and any MAC-based Winbox connections disconnect (presumably due to a timeout)
3 - After 10 to 20 seconds, the CPU returns to normal, but no data is sent over the L2TP link by the bandwidth test (although a 'ping' in a terminal window continues to work over the link)
4 - After some time (about 10 to 20 seconds), data starts transmitting again and we jump back to the top of this list with CPU at 100%. This cycle continues indefinitely.

As I said, UDP doesn't cause any problems at all, the above only happens with a TCP bandwidth test.

Any ideas anybody?

Re: RB1100 bandwidth test over L2TP link - problems

Posted: Mon Jun 14, 2010 1:20 pm
by doush
Did you try running a bandtest from a PC instead of on the router itself ?

Re: RB1100 bandwidth test over L2TP link - problems

Posted: Mon Jun 14, 2010 1:23 pm
by NAB
No, I haven't done that yet.

Re: RB1100 bandwidth test over L2TP link - problems

Posted: Mon Jun 14, 2010 2:08 pm
by NAB
Right. More information....

I have duplicated the configuration on a RB450 (ROS 3.29) and a PC (ROS 4.5) and can confirm that the same happens.

So, I am imagining that this is a side-effect of the bandwidth-test module rather than what actually happens when I load the tunnel (which I will test next).

Re: RB1100 bandwidth test over L2TP link - problems

Posted: Mon Jun 14, 2010 2:24 pm
by gdorm
There are some formulas that uses ping values and calculate link speed based on round-trip-delay!! You can try this if you feel you have some time :)

P.S. use packets with different size!

Re: RB1100 bandwidth test over L2TP link - problems

Posted: Mon Jun 14, 2010 2:36 pm
by gdorm
Here you go:
(Receive Window<= buffer size * 1000)/RTT = bits/s

Keep in mind windows sucks and uses smaller buffer ( you can change this in the reg) then linux and you will get different results(better in linux) :) ! This can be seen in high latency networks such as satelites.