ndt-users list created

[Richard Carlson <>]

Hi Kenny;

I've trimmed the email and have some comments below.

At 10:15 AM 10/17/2006, Ken Bellars wrote:
> Rich,
>
> Thanks so much for walking me through building my own NDT. The first 
> suggestion actually fixed the problem.
>
> Now its running cool but I think there is still a problem (most likely the 
> last.).
>
> My C2S speed is far greater than the S2C. See below.
>
> ---------------------------------------------------------------------------------
>
> click START to re-test
> Connected to: <http://196.207.6.22>196.207.6.22  --  Using IPv4 address
> Checking for Middleboxes . . . . . . . . . . . . . . . . . .  Done
> checking for firewalls . . . . . . . . . . . . . . . . . . .  Done
>
> running 10s outbound test ( Client -to- Server [C2S] ) . . . . . 44.25Mb/s
> running 10s inbound test ( Server -to- Client [S2C] ) . . . . . . 1.48Mb/s

This is reporting that server is unable to fully utilize the 
network.  Fortunately, the NDT "Statists" and "More Details" pages should 
help explain why.  Look at these pages and send me a copy if you need help 
interpreting the results.

> The slowest link in the end-to-end path is a 10 Gbps 10 Gigabit 
> Ethernet/OC-192 subnet

The NDT server performs some raw packet timing calculations to determine 
the bottleneck link capacity.  I suspect that you are using a new PC with a 
1 GE NIC and that NIC is doing interrupt coalescing, handling multiple 
receive packets on a single interrupt.  This means that the NDT is finding 
out how fast the NIC can transfer packets across the memory bus, not across 
the network.  Until I can fix this bug, turning interrupt coalescing off 
should correct the problem (at the expense of more CPU utilization).

> Information: Other network traffic is congesting the link

This is probably a misleading message.  My plan is to update the congestion 
detected signature in the next few months.

> [ S2C ]: Excessive packet queuing detected

This is saying that the server can send data to the NIC faster than the NIC 
can push it out into the network.  This is typical for modern servers and 
clients stuck behind slow links (DSL/Cable modem).  The word "Information" 
in blue indicated that it is a hot-link that you can click on to get more 
information.

Let us know what you find.

Rich
> click START to re-test
>
> --------------------------------------------------------------------------------- 
>
> [snip snip snip]

------------------------------------



Richard A. Carlson                              e-mail: 

Network Engineer                                phone:  (734) 352-7043
Internet2                                       fax:    (734) 913-4255
1000 Oakbrook Dr; Suite 300
Ann Arbor,  MI  48104