BASIC: ip request w/out reboot

[Neal Hogan <nealhogan%gmail.com@localhost>]

Hello and sorry for the following basic question, but I can't find the
answer to it in what I find to be a reasonable amount of time (which
may suggest that the answer is 'no).

Is there a way to request an IP without rebooting? I have an old piece
of shit that doesn't always connect at boot and I was wondering/hoping
that there was something that I could run that will ask for an IP
again (eg., /etc/netstart in oBSD).

Thanks!