dhcp-related problem in a DOCSIS cable network

[fadey]

Hi, everyone.
I have a dhcp-related problem in my cable network. When all cable modems
are being reset at once and try to get an IP, things get stuck. I see
DHCPDISCOVER message from cable modems and DHCPOFFER sent back to them.
Now a cable modem should send DHCPREQUEST, but instead it hangs out
there quiet and in a while repeats its DHCPDISCOVER message. A Cisco
CMTS is a dhcp relay agent.
When I reset cable modems one by one all goes smooth (DISCOVER, OFFER,
REQUEST and ACK).
And the most strange thing is that after I stop dhcpd for a couple of
seconds and then start it again, 3-5 cable modems manage to receive IPs.
So after a whole lot of restarts I finally have my network going again.

If anyone has experienced anything like that, please let me know.
Perhaps it is the cisco_CMTS where I should be looking for a problem,
and not dhcp.

Thanks in advance.

P.S. My network

cable_modems---Cisco_CMTS---dhcp_server