Red Hat Bugzilla – Bug 462525
TCP silly window syndrome, overly large packets > mtu
Last modified: 2009-07-14 10:22:16 EDT
Description of problem:
I'm seeing some extreme weirdness on a long-running tcp stream for a 1.2GB http file transfer. 1) packets almost 2x the MTU of the interface are being sent out to the internet.
2) I'm not getting hit with any icmp must fragments. huh????
3) the output is oscillating between 2x the desired rate and 0 with a frequency of 1 second.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Run thttpd, configure a throttle for 12.8kBytes/sec
2. have the remote end download a 1.2GByte file
3. watch the flow using fedora's network monitor. All will be well for a few hours and then oscillations in the packet flow rate will break out.
sorry, I am not sure how reproducible this is, if at all
A non-steady steady tcp flow with constant sinusoidal oscillations in the
system monitor presented "network history" curve.
packets larger than the MTU are being sent regularly.
A steady tcp flow
No packets larger than the MTU being sent
220.127.116.11-29.fc9.x86_64 #1 SMP Wed Sep 3 03:16:37 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux
eth0 Link encap:Ethernet HWaddr 00:E0:81:56:8D:67
inet addr:18.104.22.168 Bcast:22.214.171.124 Mask:255.255.255.0
inet6 addr: 2001:5a8:4:7d1::1/64 Scope:Global
inet6 addr: fe80::2e0:81ff:fe56:8d67/64 Scope:Link
inet6 addr: 2001:5a8:4:7d1::666/64 Scope:Global
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:691955 errors:0 dropped:0 overruns:0 frame:0
TX packets:484658 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:135468985 (129.1 MiB) TX bytes:684114014 (652.4 MiB)
Interrupt:23 Base address:0x6000
kernel: forcedeth: Reverse Engineered nForce ethernet driver. Version 0.61.
kernel: forcedeth 0000:00:0a.0: ifname eth0, PHY OUI 0x5043 @ 1, addr 00:e0:81:56:8d:67
kernel: forcedeth 0000:00:0a.0: highdma csum timirq gbit lnktim desc-v3
I'll add an attachment of a short wireshark tcpdump showing the oscillations and overly large packets.
Created attachment 316907 [details]
wireshark dump of the large packets and wildly oscillating flow rates
note the packets of > 2962 bytes on an interface with a 1500 byte MTU
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