Tom's Hardware > Forum > General Networking > Network General Discussions > Network Address Question?
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itfitz   08-28-2009 at 07:22:04 PM

Hello,
I have been thrown into the network roll of a repair company. We put out about 900 computers a day. We have IPcop as a firewall before a Linksys router. The green interface is set to 192.168.3.1 and 192.168.1.1 on the red. We are using Windows Server 2003 for a DHCP server set at 192.168.1.2. It is set at a scope of 192.168.1.0. We have the lease set to 1 hour.
The problem we are having is that the IP addresses are not being issued out automatically. I am thinking it is because we are running out of addresses. I would like to set the server to either add another Class C scope, or ideally a Class B scope. I am new to networking and seem to be running into a problem with internet connection after I change/ add new scope. I am assuming that it is because of being on different networks, but can’t seem to get past it.
Any help with this situation would be greatly appreciated.

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itfitz   08-28-2009 at 09:31:27 PM

itfitz wrote :

Hello,
I have been thrown into the network roll of a repair company. We put out about 900 computers a day. We have IPcop as a firewall before a Linksys router. The green interface is set to 192.168.3.1 and 192.168.1.1 on the red. We are using Windows Server 2003 for a DHCP server set at 192.168.1.2. It is set at a scope of 192.168.1.0. We have the lease set to 1 hour.
The problem we are having is that the IP addresses are not being issued out automatically. I am thinking it is because we are running out of addresses. I would like to set the server to either add another Class C scope, or ideally a Class B scope. I am new to networking and seem to be running into a problem with internet connection after I change/ add new scope. I am assuming that it is because of being on different networks, but can’t seem to get past it.
Any help with this situation would be greatly appreciated.



The units I hook up to the network will not automatically accept the IP addressess. I have to manually choose to accept IP address. It apears that the Client computer has to request an IP three times before the server offers one.

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Zenthar   08-29-2009 at 04:24:05 AM

Have you disabled the DHCP server of the Linksys router, maybe it's interfering with the Windows 2003 DHCP.

As for IP adresses, there are actually many adresses that can be used for private networks, 192.168.XXX.XXX is only one of them (256 Class C networks). You can also use 172.16-32.XXX.XXX (16 Class B networks) and 10.XXX.XXX.XXX (1 Class A).

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itfitz   08-29-2009 at 04:43:12 AM

The Linux box is th firewall. One IC goes to the Linksys router and the other to the server. It seems that the main problem isn't that I'm running low on IP addresses, it's that the units are not automatically receiving the addresses. They have 169 addresses and then I have to tell it to release and renew IP to get it to take an address.

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Zenthar   08-29-2009 at 01:34:47 PM

As to why the units don't get assigned new addresses, you might need to investigate further. Once you force the IP renewal on one of the client IP, can you make sure the lease expiration time is ok?

You could always try to intall wireshark on one of the problematic PC and start sniffing the packets to find out what is happening. Since DHCP handshake is normally done at boot, you might need a 2nd PC to sniff and a hub (not a switch) to "broadcast" the traffic to the 2nd PC. If the 2nd PC has 2 NIC, you could also just set it up as a "gateway" and still sniff the packets without a hub.

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itfitz   08-29-2009 at 11:09:25 PM

It appears that the Client is asking for it's old IP address three times before the DHCP server offers an IP address. The server is receiving the requessts( Iscanned the packets on the server also) but not responding. Then after the third time of no response the client gives up. Then I have to choose the "Automatically get a new IP sttingd for the network adapter "Local Area Connection"" Then it will accept the IP address no problem. Before they switched to the new building, with the new server, it did not do this.

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Zenthar   08-30-2009 at 01:55:00 AM

If the server does not respond to DHCP request, then perhaps THAT is the problem. When you issue a "RENEW" command, is there any difference in the request packet?

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itfitz   09-01-2009 at 04:56:53 AM

I will check this. Is there anything I should look for?

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Zenthar   09-01-2009 at 12:35:14 PM

Not precisely, but, if I remember correctly, a DHCP packet doesn't have that many fields to check.

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itfitz   09-10-2009 at 10:21:31 PM

I'm not seeing anything significant in the packets. Is there a way to make the client accept the first offer, the client might be refusing to change until it has requested its old address three times. The problem would have to be resolved on the server end as we are always hooking up new computers to the network. The average a computer is on the network is 1 hour before we ship it out.

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