ndt-users list created

[Richard Carlson <>]

Hi Matt;

Welllll it kind of reports it "Excessive packet loss is impacting your 
performance, check the auto-negotiate function on your local PC and network 
switch" and the asymmetric throughput is another clue,  but yes the 
mismatch detection algorithm failed in this case.

Here's why.

The current duplex mismatch detection heuristics is based on some 
experiments I ran several years ago.  I have been actively working on 
enhancing this part of the NDT code ever since.  The current heuristic 
using a logical AND of the following conditions.
        Congestion Window limited over 90% of the time (99.93% here)
        Theoretical speed over 2 Mbps (7.32 Mbps here)
        more than 2 packets being retransmitted per second (2.19 here)
        SSthresh value has been set (4344 Bytes here)
        Connection was idle more than 1% of the time (0 here)

So the first 4 conditions are true but the 5th is false so the condition is 
not reported.

While I am working on fixes for this problem, including a more 
mathematically rigorous model for this condition, the going is slow.  I 
need to figure out when a problem is caused by the mismatch condition and 
when it is an artifact of the specific OS/browser.  To make this problem 
harder, the condition changes when you reverse the mismatch condition (try 
setting the laptop to full and the switch to half).  Lastly, I'm trying to 
keep the false positive rate as low as possible.  I'm of the option that 
its better to fail to detect the condition than it is to falsely report it 
(and have techs running around trying to find a non-existent problem).

So all these things combined make detecting duplex mismatches a hard 
problem.  Right now, you still need someone to interpret the results to 
determine what the tool says.  But at least you have some data to work from.

Hopefully I can get a better detection algorithm out by the end of the 
year.  Keep your fingers crossed.

Rich

At 11:01 AM 11/4/2005, Matt Wilson wrote:
> Hi all-
>
> Is anyone else having trouble with duplex mismatches not being 
> diagnosed/reported by NDT?
>
> I have two NDT servers and they both are exhibiting this behavior.
> One is running RHEL kernel-2.6.9-22.EL, web100-2.5.1, and NDT 3.1.4a.
> The other is running kernel.org kernel-2.6.12, web100-2.5.4, and NDT 3.1.4a
>
> I create a duplex mismatch on the link between the edge switch and my laptop.
> Mac OS 10.3.9, Firefox Client.  ifconfig set en0 to 10baseT/UTP <half-duplex>
> Connected to Cisco 3548 FastEthernet switchport set to Full-duplex, 10 
> Mbps, 100BaseTX/FX
>
> But the applet reports that the link is Full Duplex, has no duplex errors, 
> and has network congestion.  Full report pasted below.
>
> Anyone have any ideas about what might be going on?  Thanks!
> -Matt
>
>
> Checking for Middleboxes . . . . . . . . . . . . . . . . . .  Done
> running 10s outbound test (client to server) . . . . . 83.88Kb/s
> running 10s inbound test (server to client) . . . . . . 5.09Mb/s
> The slowest link in the end-to-end path is a 10 Mbps Ethernet subnet
> Information: Other network traffic is congesting the link
> -
> WEB100 Enabled Statistics:
> Checking for Middleboxes . . . . . . . . . . . . . . . . . .  Done
> running 10s outbound test (client to server) . . . . . 83.88Kb/s
> running 10s inbound test (server to client) . . . . . . 5.09Mb/s
>
>         ------  Client System Details  ------
> OS data: Name = Mac OS X, Architecture = ppc, Version = 10.3.9
> Java data: Vendor = Apple Computer, Inc., Version = 1.3.1_16
>
>         ------  Web100 Detailed Analysis  ------
> 10 Mbps Ethernet link found.
> Link set to Full Duplex mode
> Information: throughput is limited by other network traffic.
> Good network cable(s) found
> Normal duplex operation found.
>
> Web100 reports the Round trip time = 7.06 msec; the Packet size = 1448 
> Bytes; and
> There were 219 packets retransmitted, 1038 duplicate acks received, and 0 
> SACK blocks received
> The connection was idle 0 seconds (0%) of the time
> This connection is network limited 99.92% of the time.
> Excessive packet loss is impacting your performance, check the 
> auto-negotiate function on your local PC and network switch
>
> Web100 reports TCP negotiated the optional Performance Settings to:
> RFC 2018 Selective Acknowledgment: OFF
> RFC 896 Nagle Algorithm: ON
> RFC 3168 Explicit Congestion Notification: OFF
> RFC 1323 Time Stamping: ON
> RFC 1323 Window Scaling: OFF
> Information: Network Middlebox is modifying MSS variable
> Server IP addresses are preserved End-to-End
> Client IP addresses are preserved End-to-End
> -
> WEB100 Kernel Variables:
> Client: localhost/127.0.0.1
> AckPktsIn: 2917
> AckPktsOut: 0
> BytesRetrans: 331566
> CongAvoid: 1234
> CongestionOverCount: 0
> CongestionSignals: 208
> CountRTT: 1880
> CurCwnd: 5792
> CurMSS: 1448
> CurRTO: 209
> CurRwinRcvd: 65535
> CurRwinSent: 5792
> CurSsthresh: 2896
> DSACKDups: 0
> DataBytesIn: 0
> DataBytesOut: 6893242
> DataPktsIn: 0
> DataPktsOut: 4553
> DupAcksIn: 1038
> ECNEnabled: 0
> FastRetran: 208
> MaxCwnd: 8688
> MaxMSS: 1448
> MaxRTO: 517
> MaxRTT: 201
> MaxRwinRcvd: 65535
> MaxRwinSent: 5792
> MaxSsthresh: 4344
> MinMSS: 1448
> MinRTO: 201
> MinRTT: 0
> MinRwinRcvd: 57920
> MinRwinSent: 5792
> NagleEnabled: 1
> OtherReductions: 0
> PktsIn: 2917
> PktsOut: 4553
> PktsRetrans: 219
> X_Rcvbuf: 262142
> RcvWinScale: 2
> SACKEnabled: 0
> SACKsRcvd: 0
> SendStall: 0
> SlowStart: 218
> SampleRTT: 8
> SmoothedRTT: 6
> X_Sndbuf: 262142
> SndWinScale: 0
> SndLimTimeRwin: 0
> SndLimTimeCwnd: 10065458
> SndLimTimeSender: 7011
> SndLimTransRwin: 0
> SndLimTransCwnd: 1
> SndLimTransSender: 1
> SndLimBytesRwin: 0
> SndLimBytesCwnd: 6893242
> SndLimBytesSender: 0
> SubsequentTimeouts: 0
> SumRTT: 13280
> Timeouts: 0
> TimestampsEnabled: 1
> WinScaleRcvd: 0
> WinScaleSent: 2
> DupAcksOut: 0
> StartTimeUsec: 23167
> Duration: 10075695
> c2sData: 3
> c2sAck: 3
> s2cData: 8
> s2cAck: 3
> half_duplex: 0
> link: 100
> congestion: 1
> bad_cable: 0
> mismatch: 0
> spd: 0.00
> bw: 7.32
> loss: 0.045684164
> avgrtt: 7.06
> waitsec: 0.00
> timesec: 10.00
> order: 0.3558
> rwintime: 0.0000
> sendtime: 0.0007
> cwndtime: 0.9993
> rwin: 0.5000
> swin: 2.0000
> cwin: 0.0663
> rttsec: 0.007064
> Sndbuf: 262142
> aspd: 154.98177
>
> Checking for mismatch on uplink
>         (speed > 50 [0>50], (xmitspeed < 5) [0.08<5]
>         (rwintime > .9) [0>.9], (loss < .01) [0.04<.01]
> Checking for excessive errors condition
>         (loss/sec > .15) [0.00>.15], (cwndtime > .6) [0.99>.6],
>         (loss < .01) [0.04<.01], (MaxSsthresh > 0) [4344>0]
> Checking for 10 Mbps link
>         (speed < 9.5) [0<9.5], (speed > 3.0) [0>3.0]
>         (xmitspeed < 9.5) [0.08<9.5] (loss < .01) [0.04<.01], (mylink > 
> 0) [10.0>0]
> Checking for Wireless link
>         (sendtime = 0) [7.0E=0], (speed < 5) [0<5]
>         (Estimate > 50 [7.32>50], (Rwintime > 90) [0>.90]
>         (RwinTrans/CwndTrans = 1) [0/1=1], (mylink > 0) [10.0>0]
> Checking for DSL/Cable Modem link
>         (speed < 2) [0<2], (SndLimTransSender = 0) [1=0]
>         (SendTime = 0) [7.0E-4=0], (mylink > 0) [10.0>0]
> Checking for half-duplex condition
>         (rwintime > .95) [0>.95], (RwinTrans/sec > 30) [0>30],
>         (SenderTrans/sec > 30) [0.1>30], OR (mylink <= 10) [10.0<=10]
> Checking for congestion
>         (cwndtime > .02) [0.99>.02], (mismatch = 0) [0=0]
>         (MaxSsthresh > 0) [4344>0]
>
> estimate = 7.32 based on packet size = 11Kbits, RTT = 7.06msec, and loss = 
> 0.045684164
> The theoretical network limit is 7.32 Mbps
> The NDT server has a 255.0 KByte buffer which limits the throughput to 
> 283.12 Mbps
> Your PC/Workstation has a 63.0 KByte buffer which limits the throughput to 
> 70.78 Mbps
> The network based flow control limits the throughput to 9.38 Mbps
>
> Client Data reports link is 'Ethernet', Client Acks report link is 'Ethernet'
> Server Data reports link is 'OC-48', Server Acks report link is 'Ethernet'

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



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