Problems expanding DHCP scope

[mquinn0908]

I have a DHCP scope that is 10.8.1.80-127 and I want to extend it out to 254 and I did that in the options for the scope however any clients that receive 128-254 (new extension) they can access network resources but not the internet. I do have the gateway configured in DHCP and the clients are getting the correct gateway address in both the old range and new but the new addresses can't access the internet nor can they ping the gateway. I checked my firewall and nothing is being blocked and if I statically assign an address in the new range then it gets out with no problem. I am stumped...any ideas?

Mandy
MCP/A+/Network+

 

[GlenJohnson]

Has the new scope been authorized? What does ipconfig show on the clients with problems? Good luck.

Glen A. Johnson
Johnson Computer Consulting

http://www.fred08.com/index.aspx

 

[mquinn0908]

I don't know if the new scope has been authorized or not...is there a way to tell?? Ipconfig shows that the correct IP addresses have been assigned for the gateway and dns servers but I still can not ping the gateway or access the internet.

Mandy
MCP/A+/Network+

 

[GlenJohnson]

Install and Configure DHCP in Windows Server 2003
As services go, DHCP is easy to both install and configure. However, because there are so many settings in so many places, I am willing to bet that my tutorial will unearth at least one new option that will improve your DHCP performance.

Tutorial to Install and Configure DHCP Servers
DHCP Install
Address Leases
Scope Options
Address Reservations
Authorize - DHCP Server in Active Directory
Activate - DHCP Scope
Summary
DHCP Install
This tutorial will guide you through the steps needed to get your DHCP server installed and configured correctly. Let us begin with a straightforward job to install DHCP. Get your Windows Server CD ready, then navigate to: Add Remove Programs, Windows Components, Networking Services.

Whilst adding the DHCP service is easy, configuring the scope options needs thought. For instance, if you make a mistake with the subnet mask, you cannot amend that scope, you would have to delete and start afresh. However, you can add and change the options such as Type 006 DNS server, or Type 015 Domain name.

DHCP Address Leases
Lease is a good name for a DHCP IP property. Take for example the 8 day default lease; if the client is shutdown for 2 days, when it restarts it will continue to have the same IP address. Halfway through their lease clients attempt to renew their lease. IPCONFIG /all will show you the lease, while /renew will do what it says, top up the lease.

Only reduce the duration if you are short of IP addresses. For example, if you only have 250 IP addresses but 300 possible clients. It also makes sense to set short leases if you are likely to discontinue a scope in the near future.

Here is a table summarising how a DHCP service results in clients getting an IP address. If you are interested in seeing these packets, use Network monitor to capture DHCP in action. Here are the classic 4 packets that clients exchange during a lease negotiation.

Client
Server

DHCPDiscover -->
<--- DHCPOffer

DHCPRequest -->
<--- DHCPack


DHCPInform Server check that it is Authorized in Active Directory



Note 1: DHCPRequest may seem strange, but it comes into play if there are two DHCP servers and both make an offer to a potential client.

Note 2: DHCPack. Once in a blue moon you see DHCPNack this is a negative acknowledgement which mean, ' I do no know you'. The most likely cause of Nack is the client is trying to renew an IP address from the wrong DHCP server.


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Learn more about DHCP. As an MCT trainer, I can thoroughly recommend TrainSignal because they provide practical hands on training. In particular, I like the way TrainSignal cover all learning methods, instructor lead, video and of course text material. With TrainSignal you can either take one module, for example DHCP or go for a combination of modules. See more about DHCP here


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Scope Options.
Take the time to investigate Scope Options, this the most likely place that I will win my bet that you will find a new setting which will improve your network performance. These options can be set at the Scope Level, Server Level, Reservation Level or at the Class Level (Tricky). So find all four places and make up your mind which would be the best level for your network.

Examples of DHCP Scope Options:

Router (Default Gateway), DNS Servers (006)
Domain Name (015) WINS (044 and 046)


Classes (Advanced Tab)

Vendor Class - Windows 98 Machines
User Class - Routing and Remote Access
Creating your own User Class - See more here.
Address Reservation
Reserving IP addresses is useful in two situations, for file and print servers and for important machines where leases are in short supply. How does DHCP know which machine to lease a particular IP? The answer is by its MAC address (also called NIC or Physical address). In Windows 2003 when you enter the MAC address DHCP strips out the hyphens if you absentmindedly include them amongst the HEX numbers. To find the MAC address ping the machine then type arp -a.

Remember that you can set DHCP Options for the reservations; after all, that may have been the very reason why you decided to make reservations in the first place.

Authorize - DHCP Server
In a Windows Server 2003 (or 2000) domain all DHCP servers need to be authorized in Active Directory. This is an example of Microsoft's new security initiative, and an attempt to eliminate rogue DHCP servers set up junior administrators in a large company. So, you need to logon (or RunAs) a member of the Enterprise Admins group. Then right click the DHCP server icon, and Authorize.

Incidentally, The RIS service also needs to be Authorized before it becomes active.

Activate - DHCP Scope
Even after you Authorize a server, each scope must be activated individually. So, right click the scope to activate (or deactivate). Keep your eye on the red or green arrows to judge your success. Note you may have to Refresh from the server icon, often pressing F5 is not enough.

See if this helps.



Glen A. Johnson
Johnson Computer Consulting

http://www.fred08.com/index.aspx

 

[mquinn0908]

It appears as though this server has already been activated adn authorized as the only options now available are deactivate and unauthroize.

Mandy
MCP/A+/Network+

 

[GlenJohnson]

Did you turn off the dhcp service when you expanded the scope? Just a thought.

Glen A. Johnson
Johnson Computer Consulting

http://www.fred08.com/index.aspx

 

[mquinn0908]

No the service was not stopped when the scope was expanded. I have deleted the IP's that were in the new extended range from the DHCP leases and I put the range back to the original scope so I am back to where I started. Now that I am back to where I started what is the best way to go and expand this scope to where it works properly? Thank you.

Mandy
MCP/A+/Network+

 

[GlenJohnson]

Ok, here's the deal. You should be able to just change the beginning or ending range. Don't know why you start at 10.8.1.80, but you should be able to change the end to 10.8.1.254. This will give you a range of 10.8.1.80 to 10.8.1.254. This should solve the problem. I checked and this should be able to work since NT4.0 sp6. Let us know what happens. Good luck.

Glen A. Johnson
Johnson Computer Consulting

http://www.fred08.com/index.aspx

 

[mquinn0908]

We start at 10.8.1.80 because we have servers, routers, printers and some workstations statically assigned from 1-79 so that leaves us starting at 80. I will try extending the range again tomorrow and see how that goes. Do I need to stop the DHCP service or do anything else in particular before I extend the range?

Thank you so much for all of your help.

Mandy
MCP/A+/Network+

 

[GlenJohnson]

Got the information from this article. Read it and see what you think. Don't see anything about needing to stop the services. Hope this helps.

http://support.microsoft.com/kb/255999

Glen A. Johnson
Johnson Computer Consulting

http://www.fred08.com/index.aspx