ndt-users list created

[Chris Hawkinson <>]

 After further investigation, I found that "TCP Window Scaling" is 
being negotiated to "OFF", which is obviously the reason for the smaller 
TCP buffer. Now we're off to try to determine why it is being turned 
"OFF" between this particular client and NDT server.

Thanks,
Chris

On 10/8/10 8:58 AM, Chris Hawkinson wrote:
>  Hi Everyone,
>
> I'm trying to help someone with an NDT issue.
>
> Their client machine is 32bit Linux 2.6.18 (Here's what uname says ... 
> "2.6.18-194.17.1.el5PAE #1 SMP Wed Sep 29 13:31:51 EDT 2010 i686 i686 
> i386 GNU/Linux" ).
>
> They tuned there sysctl values, as shown below...
>
> cat /proc/sys/net/ipv4/tcp_moderate_rcvbuf
> 1
>
> cat /proc/sys/net/core/rmem_max
> 8388608
>
> cat /proc/sys/net/core/wmem_max
> 8388608
>
> cat /proc/sys/net/ipv4/tcp_rmem
> 8192 87380 8388608
>
> cat /proc/sys/net/ipv4/tcp_wmem
> 8192 65536 8388608
>
> The problem is, everytime they run the NDT Java client to a remote NDT 
> server, the output shows that NDT can only get a 32k buffer (full test 
> results are below). We've rebooted the Linux machine several times, 
> but no luck.
>
> Has anyone else run into this? What are we doing wrong?
>
> Thanks,
> Chris
>
> Chris Hawkinson
> Network Performance Engineer
> CENIC
>
> Full test results....
>
> TCP/Web100 Network Diagnostic Tool v5.5.4a
> ** Starting test 1 of 1 ** Connected to: ndt2.xxxxxx.edu --
> Using IPv4 address Another client is currently being served,
> your test will begin within 540 seconds Checking for
> Middleboxes . . . . . . . . . . . . . . . . . . Done checking
> for firewalls . . . . . . . . . . . . . . . . . . . Done
> running 10s outbound test (client-to-server [C2S]) . . . . .
> 3.27Mb/s running 10s inbound test (server-to-client [S2C]) .
> . . . . . 3.08Mb/s The slowest link in the end-to-end path is
> a 100 Mbps Full duplex Fast Ethernet subnet [S2C]: Packet
> queuing detected
>
> Statistics: ===========
>
> WEB100 Enabled Statistics: Checking for Middleboxes . . . . .
> . . . . . . . . . . . . . Done checking for firewalls . . . .
> . . . . . . . . . . . . . . . Done running 10s outbound test
> (client-to-server [C2S]) . . . . . 3.27Mb/s running 10s
> inbound test (server-to-client [S2C]) . . . . . . 3.08Mb/s
>
> ------ Client System Details ------ OS data: Name = Windows
> XP, Architecture = x86, Version = 5.1 Java data: Vendor = Sun
> Microsystems Inc., Version = 1.6.0_21
>
> ------ 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 = 74.78 msec; the Packet
> size = 1448 Bytes; and No packet loss - but packets arrived
> out-of-order 71.84% of the time S2C throughput test: Packet
> queuing detected: 87.01% This connection is receiver limited
> 54.82% of the time. Increasing the the client's receive
> buffer (33.0 KB) will improve performance This connection is
> sender limited 37.76% of the time. This connection is network
> limited 7.42% of the time.
>
> 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: ON RFC 1323 Window
> Scaling: OFF
>
> Server 'ndt2.xxxxx.edu' is probably behind a firewall.
> [Connection to the ephemeral port failed] Client is probably
> behind a firewall. [Connection to the ephemeral port failed]
> Information: Network Middlebox is modifying MSS variable
> Server IP addresses are preserved End-to-End Client IP
> addresses are preserved End-to-End
>
>
> More details: ============
>
> WEB100 Kernel Variables: Client: localhost/127.0.0.1 CurMSS:
> 1448 X_Rcvbuf: 33554432 X_Sndbuf: 33554432 AckPktsIn: 1275
> AckPktsOut: 0 BytesRetrans: 0 CongAvoid: 0
> CongestionOverCount: 0 CongestionSignals: 0 CountRTT: 360
> CurCwnd: 56472 CurRTO: 274 CurRwinRcvd: 31856 CurRwinSent:
> 6144 CurSsthresh: 144800 DSACKDups: 0 DataBytesIn: 0
> DataBytesOut: 4261812 DataPktsIn: 0 DataPktsOut: 3188
> DupAcksIn: 916 ECNEnabled: 0 FastRetran: 0 MaxCwnd: 56472
> MaxMSS: 1448 MaxRTO: 277 MaxRTT: 81 MaxRwinRcvd: 34020
> MaxRwinSent: 6144 MaxSsthresh: 144800 MinMSS: 1448 MinRTO:
> 273 MinRTT: 72 MinRwinRcvd: 4328 MinRwinSent: 5792
> NagleEnabled: 1 OtherReductions: 0 PktsIn: 1275 PktsOut:
> 3188 PktsRetrans: 0 RcvWinScale: 10 SACKEnabled: 3 SACKsRcvd:
> 0 SendStall: 0 SlowStart: 0 SampleRTT: 72 SmoothedRTT: 74
> SndWinScale: 0 SndLimTimeRwin: 6068059 SndLimTimeCwnd:
> 821177 SndLimTimeSender: 4179761 SndLimTransRwin: 280
> SndLimTransCwnd: 4 SndLimTransSender: 284 SndLimBytesRwin:
> 3124388 SndLimBytesCwnd: 143960 SndLimBytesSender: 993464
> SubsequentTimeouts: 0 SumRTT: 26922 Timeouts: 0
> TimestampsEnabled: 1 WinScaleRcvd: 0 WinScaleSent: 10
> DupAcksOut: 0 StartTimeUsec: 424323 Duration: 11072093
> c2sData: 5 c2sAck: 5 s2cData: 8 s2cAck: 3 half_duplex: 0
> link: 100 congestion: 0 bad_cable: 0 mismatch: 0 spd: 3.08
> bw: 147.72 loss: 0.000001000 avgrtt: 74.78 waitsec: 0.00
> timesec: 11.00 order: 0.7184 rwintime: 0.5482 sendtime:
> 0.3776 cwndtime: 0.0742 rwin: 0.2596 swin: 256.0000 cwin:
> 0.4308 rttsec: 0.074783 Sndbuf: 33554432 aspd: 0.00000
> CWND-Limited: 134.23 minCWNDpeak: -1 maxCWNDpeak: -1
> CWNDpeaks: -1
>
> The theoretical network limit is 147.72 Mbps The NDT server
> has a 16384.0 KByte buffer which limits the throughput to
> 3423.23 Mbps Your PC/Workstation has a 33.0 KByte buffer
> which limits the throughput to 3.47 Mbps The network based
> flow control limits the throughput to 5.76 Mbps
>
> Client Data reports link is 'FastE', Client Acks report link
> is 'FastE' Server Data reports link is 'OC-48', Server Acks
> report link is 'Ethernet'