Change the subnet mask

[shoota]

I'm the IT manager for a school and I'm trying to impliment a new server into an exisiting network. While installing Server 2008 stn. I put the wrong subnet mask for the existing network. DHCP is sending this transmitting this wrong subnet even thought the NIC has the correct subnet. I've also manually edited teh registry, found two entries with the wrong subnet and modified to the correct one but still cannot get the DHCP to give out the correct subnet. I've deleted the DHCP and DNS servers and reconfigured with out success. I don't want to reinstall as I've setup all the user accounts etc before finding the problem with the incorrect subnet. Can someone help please as I've spent a day searching the internet on how to fix this small issue.

Thanks for your help from a frustrated dummy IT manager

 

[kmcferrin]

If DHCP is handing out an incorrect subnet mask then go into the DHCP Administrative console and reconfigure the scope options and set the correct subnet mask. Then wait for all of the leases to refresh and you should be set.

________________________________________
CompTIA A+, Network+, Server+, Security+
MCTS:Windows 7
MCSE:Security 2003
MCITP:Server Administrator
MCITP:Enterprise Administrator
MCITP:Virtualization Administrator 2008 R2
Certified Quest vWorkspace Administrator

 

[shoota]

Thanks for the reply kmcferrin.

However in DHCP scope options I have the DNS set to the correct ip address (the static IP of the DC) but nowhere in there can I find where to change the subnet mask. Can you please explain where I can find it.

 

[shoota]

I'm pasteing both ipconfig of the server and client...that way you can see the subnet masks are different.

Server ipconfig /all

Microsoft Windows [Version 6.0.6002]
Copyright (c) 2006 Microsoft Corporation. All rights reserved.

C:\Users\Administrator>ipconfig /all

Windows IP Configuration

Host Name . . . . . . . . . . . . : Server3
Primary Dns Suffix . . . . . . . : levin.school
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : levin.school

Ethernet adapter Local Area Connection 2:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Realtek RTL8168C(P)/8111C(P) Family PCI-E
Gigabit Ethernet NIC (NDIS 6.0)
Physical Address. . . . . . . . . : E0-CB-4E-AB-26-85
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Realtek RTL8168C(P)/8111C(P) Family PCI-E
Gigabit Ethernet NIC (NDIS 6.0)
Physical Address. . . . . . . . . : E0-CB-4E-AB-26-FA
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::51a8:4055:7e96:8789%10(Preferred)
IPv4 Address. . . . . . . . . . . : 10.116.160.2(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 10.116.160.1
DHCPv6 IAID . . . . . . . . . . . : 182504270
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-13-BD-A0-68-E0-CB-4E-AB-26-FA

DNS Servers . . . . . . . . . . . : ::1
10.116.160.2
NetBIOS over Tcpip. . . . . . . . : Enabled


Client ipconfig /all

Microsoft Windows [Version 6.1.7600]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.

C:\Users\User>ipconfig /all

Windows IP Configuration

Host Name . . . . . . . . . . . . : User-VAIO
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : levin.school

Wireless LAN adapter Wireless Network Connection:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . : levin.school
Description . . . . . . . . . . . : Intel(R) Centrino(R) Advanced-N 6200 AGN
Physical Address. . . . . . . . . : 00-23-14-48-A3-1C
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . : levin.school
Description . . . . . . . . . . . : Marvell Yukon 88E8059 PCI-E Gigabit Ether
net Controller
Physical Address. . . . . . . . . : 54-42-49-13-BB-E7
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::f8f4:86aa:bde0:efe5%11(Preferred)
IPv4 Address. . . . . . . . . . . : 10.116.160.50(Preferred)
Subnet Mask . . . . . . . . . . . : 255.0.0.0
Lease Obtained. . . . . . . . . . : Wednesday, 8 September 2010 3:07:35 p.m.
Lease Expires . . . . . . . . . . : Thursday, 16 September 2010 5:13:51 p.m.
Default Gateway . . . . . . . . . : 10.116.160.1
DHCP Server . . . . . . . . . . . : 10.116.160.2
DHCPv6 IAID . . . . . . . . . . . : 385885374
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-13-F6-32-FF-54-42-49-13-BB-E7

DNS Servers . . . . . . . . . . . : 10.116.160.2
Primary WINS Server . . . . . . . : 10.116.160.2
NetBIOS over Tcpip. . . . . . . . : Enabled

 

[theravager]

I don't believe you can change the dhcp mask, you have to create a new scope with the correct mask.

Obviously disable then delete the existing scope

 

[shoota]

Hi, thanks for the suggestion but I've done that several times already but has made no difference.

 

[kmcferrin]

I see what it is. You configured a scope using the 10.0.0.0 network addressing scheme but didn't configure an option in the scope for the subnet mask, so that when you created the DHCP scope the server assumed that the netmask should be 255.0.0.0 and you didn't change it. It does not appear that it can be changed after the fact, so you will need to crate a new scope (preferably one that doesn't overlap) and set the correct subnet mask when you define it.



________________________________________
CompTIA A+, Network+, Server+, Security+
MCTS:Windows 7
MCSE:Security 2003
MCITP:Server Administrator
MCITP:Enterprise Administrator
MCITP:Virtualization Administrator 2008 R2
Certified Quest vWorkspace Administrator

 

[shoota]

You beauty. Thanks for the suggestion. I deleted the scope and created another and took care to make sure I got it right with your suggestion above. Thanks mate, great job done!!!