dhcp wth manual adress

Posted on 2008-06-25
Last Modified: 2013-11-24
I am configuring a little group of stations 4 in all. I am siting behind a router with a subnet mask of The router will flip me addresses like T he router , I think , is a smart Cisco. Running Mac OS X  10.4.11  on these stations,  I will need fixed ip addresses but I don't have acesss to the cli on the router. I am running os x server on the same loop as these stations and I do not want to initiate any false dhcp calls to other PC/s that are on the subnet. When I configure these machines with addresses of through 4 using the manual addressing with dhcp I am able to get to the internet so I think that means the router supports DHCPINFORM. Am I achieving my goals of getting a fixed ip for my clients without causing trouble down the line with address conflicts. I do not want my Server which sits behind the same router and get its ip vis a v dhcp lease from the Cisco router to be providing any ip address on this subnet. Am I understanding dhcp with manual adress correctly or could I just as well assign them a standard fixed ip adress and achieve the same desired result.
Question by:pheidius
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LVL 13

Expert Comment

ID: 21881343
Just make sure you assign them IP addresses that are outside the DHCP scope that is configured on the router.
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Author Comment

ID: 21892091
How can  I tell what is outside the scope of the router without cli acess? And do you mean just a fixed ip address or the Mac  dhcp with manual address option. I do want these machines to have internet access. I had read this defintion of dhcpinform "DHCPInform is a DHCP message used by DHCP clients to obtain DHCP options. While PPP remote access clients do not use DHCP to obtain IP addresses for the remote access connection, Windows 2000 and Windows 98 remote access clients use the DHCPInform message to obtain DNS server IP addresses, WINS server IP addresses, and a DNS domain name. The DHCPInform message is sent after the IPCP negotiation is concluded.

The DHCPInform message received by the remote access server is then forwarded to a DHCP server. The remote access server forwards DHCPInform messages only if it has been configured with the DHCP Relay Agent.. Click here to find out more! " 
My fuzzy understanding of this led me to think/hope that the "manual ip with dhcp" option would mean that the router would give me a permanent lease on the IP's I assigned and not try to flip these ip's to any other pc machine logging on to the domain(to which my machines will not belong." I tried this out on the thursday and, at first, I got a couple of in use by (mac address) messages(one on each machine as I configured but then no other messages occurred during the next couple of days. Probably tmi here so I guess my main question still resolves down to the. "How can I tell what is outside the scope of the router?" I can safely guess the number of  actual machines in my loop
if that helps
LVL 13

Expert Comment

ID: 21893555
Any static IP addresses need to be outside the range of the DHCP pool.
Otherwise the DHCP server may hand out those IP addresses and you'll get an IP conflict.
The DHCP server has no way of knowing about those static IP addresses.

If you must use static IP addresses within the range of the DHCP pool, then you need to configure exceptions on the DHCP server.
LVL 19

Author Comment

ID: 21894787
K that is good to know. I was misinterpreting the dhcp with manual adresss option then. So how do I know what is out of the router's range and can I still get internet connectivity if I am out of the range.
LVL 13

Accepted Solution

kdearing earned 500 total points
ID: 21894935
You can still get out as long as you are still in the same subnet as the router (default gateway).

for example:

typical DHCP settings
  range             -
  subnet mask 
  default gateway

In the above situation, static IP between  .2 - .99  and  .201 - .254
will work fine.

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