Hello, I am setting up a small network and trying to verify throughput levels between machines, but I am seeing some odd behavior. Specifically, I am seeing slow throughput in one direction between two machines, but not in the other. I am using each of the machines built in NICs (same mobo for both, Intel D975XBX, also same CPU and ram), both of which are gigabit adapters. Latency between the machines is < 1ms. They are both attached to a Netgear GS724T switch by CAT5E cables, but I have rerun these tests with just a CAT6 crossover cable between them with no change in results, so the cables and the switch should be irrelevant.
The first machine is Windows XP SP2 with no firewall software of any kind - 192.168.1.32 (Bender)
The second machine is Fedora Core 5 with no firewall rules and defaults to ACCEPT - 192.168.1.33 (InfoSphere)
My results (using iperf) are as follows:
Bender receive TCP (8k buffer on Bender, 16k buffer on Infosphere)
[1844] local 192.168.1.32 port 5001 connected with 192.168.1.33 port 42011
[ ID] Interval Transfer Bandwidth
[1844] 0.0-60.0 sec 6.53 GBytes 935 Mbits/sec
Bender receive UDP (8k buffer on Bender, 124k buffer on Infosphere)
[1932] local 192.168.1.32 port 5001 connected with 192.168.1.33 port 32797
[ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams
[1932] 0.0-60.0 sec 6.57 GBytes 940 Mbits/sec 0.013 ms 29005/4825353 (0.6%)
[1932] 0.0-60.0 sec 1 datagrams received out-of-order
Infosphere receive TCP (8k buffer on Bender, 85.3k buffer on Infosphere)
[1916] 0.0-60.0 sec 2.04 GBytes 293 Mbits/sec
Infosphere receive UDP (8k buffer on Bender, 124k buffer on Infosphere)
[1916] 0.0-60.0 sec 338 MBytes 47.3 Mbits/sec 1.162 ms 0/241397 (0%)
[1916] Sent 241397 datagrams
I have repeated these tests multiple times with the same results, when data is sent from the InfoSphere to Bender I get very good (nearly the full 1000 Mbit) speeds, but from Bender to the InfoSphere is much slower, and even much slower still for UDP.
From Bender:
GlobalMaxTcpWindowSize: 400000
Tcp Receive Window: 400000
Window Scaling: Yes
Time Stamping: Yes
Selective Acks: Yes
MTU: 1500
From InfoSphere:
net.ipv4.tcp_moderate_rcvb
uf = 1
net.ipv4.tcp_rmem = 4096 87380 4194304
net.ipv4.tcp_wmem = 4096 16384 4194304
net.ipv4.tcp_mem = 393216 524288 786432
net.ipv4.tcp_dsack = 1
net.ipv4.tcp_ecn = 0
net.ipv4.tcp_reordering = 3
net.ipv4.tcp_fack = 1
net.ipv4.tcp_sack = 1
net.ipv4.tcp_window_scalin
g = 1
net.ipv4.tcp_timestamps = 1
net.core.rmem_default = 126976
net.core.wmem_default = 126976
net.core.rmem_max = 108544
net.core.wmem_max = 108544
