Messages in this thread | | | Date | Mon, 26 Feb 2001 11:11:16 -0500 | From | Jeremy Jackson <> | Subject | Re: tcp stalls with 2.4 (but not 2.2) |
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Brian Grossman wrote:
> I'm seeing stalls sending packets to some clients. I see this problem > under 2.4 (2.4.1 and 2.4.1ac17) but not under 2.2.17.
compiled in ECN support? SYNcookies? try disabling through /proc tcp or udp? if udp check /proc/net/ipv4/ip_udpdloose or such
> > > My theory is there is an ICMP black hole between my server and some of its > clients. Is there a tool to pinpoint that black hole if it exists?
ping is your friend. -s lets you set size of packet. (to check for fragmentation) use tcpdump to capture a trace of this or a tcp session.
email trace to me private if you want.
> > > Can anyone suggest another cause or a direction for investigation? > > Why does this affect 2.4 but not 2.2? > > The characteristics I've discovered so far: > > From strace of the server process, each write to the network is > preceeded by a select on the output fd. The select waits for a > long time, after which the write succeeds. > > The packets are received by the client a couple minutes after my > server sends them. > > The clients I have tested with are win98 and winNT. > > The router for both 2.4 and 2.2 servers is running 2.2.18 with > ipvs (ipvs-1.0.2-2.2.18). > > That router does not block any ICMP. > > The behavior occurs on the 2.4 machine whether the packets are > routed directly or are mangled by ipvs. > > I've tried the same machine with both 2.4 and 2.2, as well as > another machine with just 2.2. 2.2 works. 2.4 doesn't. > > Both of my servers and the router I mentioned have two tulip > network cards. > > The clients I've tested with are behind a modem through earthlink. > Another I suspect to have same problem is behind a modem > through Juno. > > I've tried adjusting both /proc/sys/net/ipv4/route/min_adv_mss and > /proc/sys/net/ipv4/route/min_pmtu downward. Do these require an > ifconfig down/up to take effect? >
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