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DHCP on the Server vs DHCP on the Router

Posted on 2013-10-30
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Last Modified: 2013-11-01
Hello,

DHCP is active on my server 2003. My new ISP is giving me 16 Public IPs. Right now we are no using any Public IPs. So my ISP decided no activate the DHCP on the Router for those 16 public IPs, they say to avoid conflict with the DHCP on my server.

My questions:

1. Can occur a conflict if my DHCP on the server give IPs to my workstations and the Router has his own DHCP to manage the 16 public ips?

2. My ISP can do not activate the DHCP on the router but can assign me a static public IPs to my computer?

3. Do you know how the DHCP on the router assign these public IPs to my workstations.

I am not familiar with these and I need to know if the ISP is correct.

Thank you
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Question by:Agnes Sevilla
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Expert Comment

by:Rodney Barnhardt
ID: 39612463
There are a number of factors here. One, you really need a firewall between your router and your internal network, unless this router has a built in one you did not mention.

Yes, if by change the DHCP service on the router was handing our any IP address in the same range as the one your 2003 server is handing out, then there will be conflicts detected. This is because no two devices on a network can have the same IP address. Since clients would be getting them from different sources, the lease times, etc are all not known by the other service, so it will conflict.

Yes, if the router will pass the traffic to your internal machines, then you can statically set an external IP address on your internal computers.

It would assign it by answering a DHCP IP request it receives from the client, it will then answer with an assigned IP address.
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Author Comment

by:Agnes Sevilla
ID: 39613969
Hello,

Yes my private network is connected to a Firewall and this Firewall is connected to a router.

My DHCP on the server (private network) has this range 10.28. . x and netmask 255. . .240 My ISP says the range for the 16 public IPs is 12. . .y Netmask 255. . 255.0

I am still confuse since my ISP told me that I have 16 public Ips available in case I need it.

I did a test on my network:

1. I check every computer in my private network every of these have his own internal Ip but a common Public Ip (I tested this using Whoismyip)

2. Except two computers. These has 10.28. .x and 10.28. .y but their public IP are 12. . .185 and 12. . .186 (using whoismyip)

How this public Ips were assigned to these computers?

Is the DHCP on the router active or assign these IPs statically?

Can you explain me?
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Accepted Solution

by:
Rodney Barnhardt earned 2000 total points
ID: 39614330
Basically, you would not want to use the external IP addresses directly on any internal IP addresses. When they say you have 16 external IP addresses, that is based on the "block" of addresses you purchased. Typically, what you would do is if you have an outside service like a website, web mail, VPN, etc, you would configure one one of these outside IP addresses so that users can hit your network, then the firewall would have a rule to pass traffic on that IP and Port to the internal network device providing that service. I know of no good reason to use DHCP on external addresses.
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