cable modem problem

hi
I want to setup my cable modem under OpenBSD. I did not configure my network while installing the system.
When I type, I get
# ifconfig -a
lo0 : ....
...
...
rl0 : ....
...
...
vr0 : ...
...
...

I have two network cards (the machine will be a router).
I created /etc/hostname.rl0 and /etc/hostname.vr0 files and write "dhcp" into both files (I don't know which card is rl0 and vr0). When I run
sh /etc/netstart rl0
sh /etc/netstart vr0
the system starts to DHCPDISCOVER and get nothing from DHCP! The modem is connected to interface.
What is tha problem?

Thanks....

man rl & man vl...

rl0 - RealTek network cards...