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DHCP Setup Help !!! not responding to DHCP requests!

Posted on 2007-10-08
Medium Priority
Last Modified: 2010-04-18
My connection is setup like this

T1 -> Cisco 1721 router -> switch -> server, workstations, net printers..etc.

AD is installed, and dcpromo'd. DNS configured correctly.

now i want to run DHCP on this server, the DHCP on the cisco router is turned off. (we were using the DSL router as DHCP before)

We are assigned static IPs from our ISP, like below

usable IP range: -
Broadcast address:
router IP
subnet mask:
DNS 1:
DNS 2:

1st NIC is setup as static IP like above, I assigned to the server, 2nd NIC is disabled for now.

so I setup the DNS on the server, and in the NIC properties, DNS is setup to the server IP, and in DNS forwarder i set it to forward all queries to our ISP DNS /3

the server has access to internet and everything.

DHCP is setup like this
Start IP:
End Ip :
Scope Option>Router> (T1 router)
Scope Option>DNS Server> /3

while on the workstations, they are not getting any DHCP response at all.

Did i assign wrong IPs in that DHCP table?

I do not want to assign real IPs to workstations, I want to assign private block of IPs to the internal machines, like how it was before with the DSL router.

Can anyone point me to the right direction? Please help!!
Question by:mike2016
  • 3

Expert Comment

ID: 20038383
You would either need to enable that second NIC and assign it an internal address to do this, or as I would do, I would have a firewall with NAT turned on and your server would only use one NIC with an internal adress assigned.

However, since you have already DC'd it, changing the IP could be bad. You should probably enable the 2nd NIC. Is this SBS premium with ISA?
You would have the 2nd NIC in the same switch as the PC's. The primary NIC would go into the router. The switch the PC's are on, would not be plugged into the router.

Author Comment

ID: 20038419
that was quick!  this is a Win2003 R2 Standard Edition, running on DELL 2950 server

so to make the DHCP work for the internal workstations,
I enable the 2nd NIC, and I assign it an internal address such as ?  and it will start leasing out private IPs ?    what gateway IP will the NIC use?

but if I connect the Router to 1st NIC,  then 2nd NIC to our internal network,  how will the 1st and 2nd NIC communicate?   in that case they are on two seperate networks.  1 is public network, other is internal.  our internal workstations need to have access to internet as well using the same T1 line.


Accepted Solution

bkellyboulderit earned 2000 total points
ID: 20038470
It's late, but... you can use the server as a router to route the packets from internal to external. I believe you will leave the gateway empty and use network bridging.


You would set up DNS on the internal NIC to point to the internal IP of the server (itself).


You would tell DHCP to hand out the addresses using DNS of not the public ips....

requests would come to the server and then route out, and vice versa.

Read the stuff carefully before experimenting on your network.
Don't use ICF or ICS on your domain controller, per the article.

I would make sure your server is behind a firewall. I don't trust Windows in the open....

Expert Comment

ID: 20038474
PS> WINS would also be in DHCP

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