ndt-users list created

[Richard Carlson <>]

Hi Teresa;

Well, the first thing I noticed was that both directions reported under 1 
Mbps on a path that should be 100 Mbps Fast Ethernet.  So I'd suspect 
something other than a buffer problem.  Looking further I see the loss rate 
is 1.35%, which is extremely high.  I also extracted this from the data below
PktsIn: 82
PktsOut: 520
PktsRetrans: 201

This means that only 520 packets were sent in the 10 second test period 
(server-to-client).  And nearly 40% of them were duplicates.  In addition 
only 82 ACK packets were returned, with only 2 duplicate ACKs.  Thus it 
appears that the majority of Data packets were lost in the network.

I'd suggest the following:

1) run the /sbin/ifconfig command on the NDT server and look at the RX & TX 
error counters.  Are any of them high?  If so, then something is wrong with 
the local cable/switch

2) run the /bin/netstat -s command on the NDT server and look at the 
counters.  Does anything stand out as unusual?  Do any of the loss counters 
show large values?

3) look at the switches and routers in the path.  Does one of the 
interfaces show a large number of errors or collisions?  If so, look at 
that link (replace the cable/fiber or try another interface).

A 1 % loss rate will pretty much kill a TCP flow.  Chances are that 
something is causing loss in the server to client direction.  Once you 
find/fix that problem you can look into server tuning issues.

Rich

At 11:52 AM 3/16/2006, Teresa Beamer wrote:

> I've finally gotten some time to review the statistics we've been 
> gathering via
> NDT and I am consistently seeing a low kb/s for NDT server to Client with a
> high kb/s from Client to NDT server.  I'm beginning to think I need to adjust
> some parameters on the NDT server, but am not quite sure where to make the
> changes (I'm fairly new to linux).  I've included sample below of a run 
> from my
> machine.  I did notice this time a line that says: "The NDT server has a 214.0
> KByte buffer which limits the throughput to 208.98 Mbps."
>
> Should I make changes to the buffers on the server?  And if so where do I 
> go to
> make those changes.  A pointer to documentation that describes this 
> information
> would be great.
>
> Thanks for any help you can provide.
>
> Teresa Beamer
> Computing Services
> Denison University
>
> TCP/Web100 Network Diagnostic Tool v5.3.3e
> click START to begin
> Checking for Middleboxes . . . . . . . . . . . . . . . . . .  Done
> running 10s outbound test (client to server) . . . . . 863.86Kb/s
> running 10s inbound test (server to client) . . . . . . 237.58kb/s
> The slowest link in the end-to-end path is a 100 Mbps Full duplex Fast 
> Ethernet
> subnet
>
> WEB100 Enabled Statistics:
> Checking for Middleboxes . . . . . . . . . . . . . . . . . .  Done
> running 10s outbound test (client to server) . . . . . 863.86Kb/s
> running 10s inbound test (server to client) . . . . . . 237.58kb/s
>
>         ------  Client System Details  ------
> OS data: Name = Windows XP, Architecture = x86, Version = 5.1
> Java data: Vendor = Sun Microsystems Inc., Version = 1.4.2_03
>
>         ------  Web100 Detailed Analysis  ------
> 100 Mbps FastEthernet link found.
> Link set to Full Duplex mode
> No network congestion discovered.
> Good network cable(s) found
> Normal duplex operation found.
>
> Web100 reports the Round trip time = 8.0 msec; the Packet size = 1460 
> Bytes; and
> There were 201 packets retransmitted, 2 duplicate acks received, and 5 SACK
> blocks received
> The connection stalled 1 times due to packet loss
> The connection was idle 0.21 seconds (1.5%) of the time
> This connection is network limited 99.87% 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: ON
> RFC 896 Nagle Algorithm: ON
> RFC 3168 Explicit Congestion Notification: OFF
> RFC 1323 Time Stamping: OFF
> RFC 1323 Window Scaling: OFF
> Packet size is preserved End-to-End
> 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: 82
> AckPktsOut: 0
> BytesRetrans: 292165
> CongAvoid: 67
> CongestionOverCount: 0
> CongestionSignals: 7
> CountRTT: 1
> CurCwnd: 7300
> CurMSS: 1460
> CurRTO: 208
> CurRwinRcvd: 0
> CurRwinSent: 5840
> CurSsthresh: 2920
> DSACKDups: 0
> DataBytesIn: 0
> DataBytesOut: 785985
> DataPktsIn: 0
> DataPktsOut: 520
> DupAcksIn: 2
> ECNEnabled: 0
> FastRetran: 1
> MaxCwnd: 7300
> MaxMSS: 1460
> MaxRTO: 208
> MaxRTT: 8
> MaxRwinRcvd: 0
> MaxRwinSent: 5840
> MaxSsthresh: 2920
> MinMSS: 1460
> MinRTO: 208
> MinRTT: 8
> MinRwinRcvd: 2147483647
> MinRwinSent: 5840
> NagleEnabled: 1
> OtherReductions: 5
> PktsIn: 82
> PktsOut: 520
> PktsRetrans: 201
> X_Rcvbuf: 219136
> RcvWinScale: 2147483647
> SACKEnabled: 3
> SACKsRcvd: 5
> SendStall: 0
> SlowStart: 13
> SampleRTT: 8
> SmoothedRTT: 8
> X_Sndbuf: 219136
> SndWinScale: 2147483647
> SndLimTimeRwin: 0
> SndLimTimeCwnd: 14495340
> SndLimTimeSender: 19349
> SndLimTransRwin: 0
> SndLimTransCwnd: 1
> SndLimTransSender: 1
> SndLimBytesRwin: 0
> SndLimBytesCwnd: 785985
> SndLimBytesSender: 0
> SubsequentTimeouts: 5
> SumRTT: 8
> Timeouts: 1
> TimestampsEnabled: 0
> WinScaleRcvd: 2147483647
> WinScaleSent: 2147483647
> DupAcksOut: 0
> StartTimeUsec: 15742
> Duration: 14520643
> c2sData: 5
> c2sAck: 5
> s2cData: 7
> s2cAck: 4
> half_duplex: 0
> link: 100
> congestion: 0
> bad_cable: 0
> mismatch: 0
> spd: 0.00
> bw: 12.00
> loss: 0.013461538
> avgrtt: 8.00
> waitsec: 0.21
> timesec: 14.00
> order: 0.0244
> rwintime: 0.0000
> sendtime: 0.0013
> cwndtime: 0.9987
> rwin: 0.0000
> swin: 1.6719
> cwin: 0.0557
> rttsec: 0.008000
> Sndbuf: 219136
> aspd: 0.30399
>
> Checking for mismatch on uplink
>         (speed > 50 [0>50], (xmitspeed < 5) [0.86<5]
>         (rwintime > .9) [0>.9], (loss < .01) [0.01<.01]
> Checking for excessive errors condition
>         (loss/sec > .15) [9.61>.15], (cwndtime > .6) [0.99>.6],
>         (loss < .01) [0.01<.01], (MaxSsthresh > 0) [2920>0]
> Checking for 10 Mbps link
>         (speed < 9.5) [0<9.5], (speed > 3.0) [0>3.0]
>         (xmitspeed < 9.5) [0.86<9.5] (loss < .01) [0.01<.01], (mylink > 
> 0) [100.0>0]
> Checking for Wireless link
>         (sendtime = 0) [0.00=0], (speed < 5) [0<5]
>         (Estimate > 50 [12.0>50], (Rwintime > 90) [0>.90]
>         (RwinTrans/CwndTrans = 1) [0/1=1], (mylink > 0) [100.0>0]
> Checking for DSL/Cable Modem link
>         (speed < 2) [0<2], (SndLimTransSender = 0) [1=0]
>         (SendTime = 0) [0.0013=0], (mylink > 0) [100.0>0]
> Checking for half-duplex condition
>         (rwintime > .95) [0>.95], (RwinTrans/sec > 30) [0>30],
>         (SenderTrans/sec > 30) [0.07>30], OR (mylink <= 10) [100.0<=10]
> Checking for congestion
>         (cwndtime > .02) [0.99>.02], (mismatch = 0) [0=0]
>         (MaxSsthresh > 0) [2920>0]
>
> estimate = 12.0 based on packet size = 11Kbits, RTT = 8.0msec, and loss =
> 0.013461538
> The theoretical network limit is 12.0 Mbps
> The NDT server has a 214.0 KByte buffer which limits the throughput to 208.98
> Mbps
> Your PC/Workstation has a 0 KByte buffer which limits the throughput to 0 Mbps
> The network based flow control limits the throughput to 6.96 Mbps
>
> Client Data reports link is 'FastE', Client Acks report link is 'FastE'
> Server Data reports link is 'GigE', Server Acks report link is 'T3'

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



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