Network is blocked till ping is issued

[DI BACCO ANTONIO - technolabs]

I have two hosts 100.1.0.1 (NotLinux) and 100.1.0.2 (linux-2.6.19.2) on
a vlan.
On the linux box the vlan interface is created with vconfig and is
attached to a Virtual PHY (fixed PHY).
When Linux box starts up, NotLinux wants to setup a TCP connection with
"Linux box" and sends a SYN packet receiving no answer from "Linux box".
If from the console of "Linux box" I issue a ping to NotLinux then,
after a while, the linux box starts responding to Windows.

Bye,
Antonio.