I set mIRC up to use ports between 2121 and 2123 (no random ports!) in options connect -> options -> advanced.
and checked "DCC" and "Other".
still mIRC is trying to use different ports. (I tried four times. It used ports from 1703 - 1707. checked with debug on.)
$portfree for the ports 2121, 2122 and 2123 is $true.

What version of mirc, and what other useful information can you give? I haven't been able to duplicate this myself on 6.16/winXP using the same settings, or any others.

I am using mIRC 6.16.
I am in a LAN and behind a router to access the internet.
I am able to make mIRC use the correct IP for Dcc-Send with /localinfo <ip>, but it does not use the specified ports.
I think that's all I can say.

Oh wait!
mIRC is using random ports when the specified ports are not free ($portfree(..) is false).
Somehow those ports aren't free anymore here, and that's whay mIRC is using random ports
My fault, sorry.

Thanks anyway,
ChosenOne