Kernel 2.4.x and IP Problems

[Gabriele Kayser <Gabriele.Kayser@globetrotter.de>]

  Hello,

  I use an application, which connects over internet to an other
  machine on high port (56003 / 56005).

  Since I upgraded to kernel 2.4.5 (with packages from A. Bunk) I get
  no connection to this other machine.

  For testing I made "telnet remote.machine.tld 56003"

  With tcpdump or netstat I see "SYN_SENT", but nothing reaches the
  the other side.
  Booting with kernel 2.2.17 - all works fine.

  All other network-connections works with 2.4.x too.

  Are there any changes in tcp/ip in kernel 2.4.x?
  Are there any kernel-variables I have to set to proper values?

  Ciao
  Gabriele