Question

Configuring DHCP relay with these variables

Asked by: 53tin

Hi experts,

I have quite an interesting problem that I need a little bit of help on, and a fresh perspective as well. I'm working in a production enviroment that is just now seeing the necessity of putting in a dedicated controls network for the production side, to ensure in house service, and better reliability. Let me start off by explaining my setup, as it's quite a curious one.

Each business inside the plant has its own dedicated VLAN, with a total of about ten to fifteen in all. I'm in the early stages of planning and implementing the new network, and have installed a catalyst 4507 to act as my core switch. This core switch connects back to a catalyst 6509 that acts as a layer 3 gateway switch, routing traffic throughout the plant. It's designed to pick up traffic from the different switches with production equipment contained on them and route them to a checkpoint firewall also connected to the 6509. The checkpoint authenticates each IP and allows them whatever acceess they require to whereever. This part of the equation works fine. What I'm doing is setting up DHCP on a Windows Server 2003 box, and using DHCP relay on the checkpoint to route DHCP requests to the server. I've tested my DHCP, and it works on the VLAN the server is in, however I can't get it to route to any other VLANs outside that one. I don't know if the checkpoint or the 6509 are set up to allow the correct things through, I don't have rights to touch either one of those, but then I'm also unsure what to touch even inside those. I've set up DHCP snooping inside my 4507, and haven't caught any traffic as of yet. Could there be something not configured right that I need to check? There's a lot of variables to consider, and that's what makes this such a mess really... Thank you for the help, and anymore clarification that's needed, I'll try and give it.

This Question has been solved and asker verified All Experts Exchange premium technology solutions are available to subscription members.

Subscribe now for full access to Experts Exchange and get

Instant Access to this Solution

  • Plus...
  • 30 Day FREE access, no risk, no obligation
  • Collaborate with the world's top tech experts
  • Unlimited access to our exclusive solution database
  • Never be left without tech help again

Subscribe Now

Asked On
2009-06-21 at 06:09:25ID24509316
Tags

Microsoft

,

Server

,

2003

,

Catalyst

,

4507

,

6509

,

VLAN

,

DHCP

,

relay

,

Checkpoint

Topics

Dynamic Host Configuration Protocol (DHCP)

,

Network Operations

Participating Experts
2
Points
500
Comments
7

Trusted by hundreds of thousands everyday for fast, accurate and reliable tech support.

  • "The time we save is the biggest benefit of Experts Exchange to Warner Bros. What could take multiple guys 2 hours or more each to find is accessed in around 15 minutes on Experts Exchange." Mike Kapnisakis, Warner Bros.
  • "Our team likes having a resource that is more secure than just using Google and most experts using this service really know their stuff. It's nice to look here first versus using Google." Dayna Sellner, Lockheed Martin
  • "Anytime that I've been stumped with a problem, 9 out of 10 times Experts Exchange has either the accepted solution or an open discussion of the potential solution to the problem." Kenny Red, eBay Inc.

See what Experts Exchange can do for you.

Got a question?

We've got the answer.

Experts Exchange has been collecting answers to technology questions since 1996…3 million and counting! If you have a question, chances are we already have your answer.

Screenshot of Experts Exchange Knowledgebase

Need individual assistance?

Our experts are ready to help.

If you can't find the exact answer you're looking for, ask our exclusive community of 50,000 experts. You’ll get a personalized answer from a trusted professional.

Screenshot of Experts Exchange Knowledgebase

Want to learn from the best?

Read articles from industry experts.

Thousands of free tech tips, tricks, how-to’s and tutorials are available in our peer reviewed articles section. See for yourself how smart our experts are, no login required.

Screenshot of an Article

Working on a long term project?

Store your work and research.

Save solutions to your questions, answers you’ve discovered through searching plus helpful articles in your personal knowledgebase for easy future access.

Screenshot of Experts Exchange Knowledgebase

Access the answers to your technology questions today.

Subscribe Now

30-day free trial. Register in 60 seconds.

What Makes Experts Exchange Unique?

Members of the expert community talk about why the experience at Experts Exchange is different than what you will find anywhere else.

Trusted by the world's most respected brands.

image of each brand's logo

Faithfully serving IT professionals since 1996.

Experts Exchange Logo

Try it out and discover for yourself.

Subscribe Now

30-day free trial. Register in 60 seconds.

Related Solutions

  1. VLAN and DHCP
    I need to split my network into 4 vlans (1 per building on campus). I currently use the 3060 Pro as my dhcp server located in my admin building for everyone, all switches are Cisco. Anyone have an idea how to config dhcp so that the outlying vlans will still be able to get th...
  2. DHCP Smart Relay?
    Does anyone know what I would use a DHCP Smart Relay for on a switch? We have one DHCP Server that is not servicing one specific subnet even after using IP Helper Addresses and I'm trying to figure out if this Smart Relay has anything to do with it.
  3. DHCP relaY
    We have layer 3 switch with 3 subnets and just migrated DHCP server. Where should we change DHCP relay setting so that other subnets would see DHCP server
  4. 3com not relaying DHCP across vlans
    Hi everyone, I am having a problem with my 3com 5500G-EI relaying dhcp. The dhcp requests needing relayed are coming into Port 1 on the 3com switch. The dhcp requests r for clients on vlan99 and vlan100. I've attached the config. Help! What am I doing wrong?

Free Tech Articles

  1. WARNING: 5 Reasons why you should NEVER fix a computer for free.
    It is in our nature to love the puzzle. We are obsessed. The lot of us. We love puzzles. We love the challenge. We thrive on finding the answer. We hate disarray. It bothers us deep in our soul. W...
  2. SCCM OSD Basic troubleshooting
    SCCM 2007 OSD is a fantastic way to deploy operating systems, however, like most things SCCM issues can sometimes be difficult to resolve due to the sheer volume of logs to sift through and the dispe...
  3. Migrate Small Business Server 2003 to Exchange 2010 and Windows 2008 R2
    This guide is intended to provide step by step instructions on how to migrate from Small Business Server 2003 to Windows 2008 R2 with Exchange 2010. For this migration to work you will need the fo...
  4. Create a Win7 Gadget
    This article shows you how to create a simple "Gadget" -- a sort of mini-application supported by Windows 7 and Vista. Gadgets can be dropped anywhere on the desktop to provide instant information, ...
  5. Outlook continually prompting for username and password
    There have been a lot of questions recently regarding Outlook prompting for a username and password whilst using Exchange 2007. There are a few reasons why this would happen and I will try to cover t...
  6. Backup Exchange 2010 Information Store using Windows Backup
    There seems to be quite a lot of confusion around the ability to backup Exchange 2010 using the built in Windows Backup feature. This stems from the omission of this feature prior to Exchange 2007 s...

Cloud Class Webinars

  1. Avoiding Bugs in Microsoft Access
    Alison Balter takes and in-depth look at avoiding bugs in Access. In this webinar you will learn about using the immediate window to debug your applications, invoking the debugger, using breakpoints to troubleshoot, stepping through code, setting the next statement to execute, ...
  2. Top 10 Best New Features in Visio 2010
    Scott Helmers gives live demonstrations of the top 10 new features in Visio 2010. This webinar will teach you how to create compelling diagrams by adding shapes to the page with a single click, linking the shapes in a diagram to data in Excel (or SQL Server, or SharePoint), ...
  3. IT Consultant Business Secrets Revealed
    Michael Munger, Experts Exchange tech pro and IT consultant, pulls back the curtain on his very successful businesses and answers question on every IT consultant and business owner should know about. He shares secrets on what he did to solve the 5 most common problems in IT, ...
  4. Disaster Recovery and Business Continuity
    Quest CTO, Mike Billon, gives an overview of the steps involved in building a dunamic disaster recovery plan. Through case studies and an examination of software/hardware tooles for monitoring and testing, you'll gain a better understandin of where you are, where you want ...
  5. Organize Your Visio Diagrams with Containers and Lists
    Scott Helmers uses cross functional flowcharts, wireframe diagrams, data graphic legends and seating charts to teach you: how to ustilize all three new structured diagram components in Visio 2010, the best practices for organizeing shapes in previous version of Visio, how to organize ...
  6. How to Us Objects, Properties, Events and Methods in Microsoft Access
    Alison Dalter gives an in-depbth look at objects, properties, events and methods in Microsoft Access. In this webinar you will learn about using the object browser, referring to objects, working with properties and methods, working with object variables, understanding the ...

Join the Community

Give a Little. Get a Lot.

Join the community of experts here and help other tech pros by answering question in your area of expertise. You can earn FREE access to all Experts Exchange's premium features and resources.

Join the Community

Answers

 

by: sorrilloPosted on 2009-06-21 at 06:16:47ID: 24677300

I am not sure if I understood your network map definition but I just want to point out that there must be a DHCP relay on every broadcast domain, on every VLAN. Is that how is it configured ?

The Windows Server must have a DHCP zone for every VLAN, it will be able to assign the correct IP based on the information provided by the DHCP relay.

 

by: grsteedPosted on 2009-06-21 at 09:24:27ID: 24677803

sorrillo is correct that you need a DHCP relay on each VLAN to forward DHCP requests to the server.

This can be done on the 6509 using the the "ip helper-address" command on each VLAN interface.  To configure the command simply do this;

conf t
 
int vlanX  (where X is the VLAN number)
ip helper-address w.x.y.z  (where w.x.y.x is the DHCP server IP address)

exit

This link gives a little more info.

http://www.cisco.com/en/US/docs/ios/12_1/iproute/command/reference/1rdipadr.html#wp1018606

Since you do have rights to touch it, you will need to get your network guy to do that for you.

Cheers,
Gary

 

by: 53tinPosted on 2009-06-22 at 03:32:25ID: 24681033

So every hop in between the router and server has to have the helper address put in it? I've got right now 3-4 switches in between each VLAN and the servers. Is there anything else that needs to be done? I've got the scopes set up on the server, is that the same as the zone, or something else? If I put the same server address for each VLAN, how will it know where to route the traffic back to? Is that everything on the server that needs to be done? I'm new to the DHCP relay, and want to make sure I get it right. Thanks!

 

by: sorrilloPosted on 2009-06-22 at 04:13:45ID: 24681231

DHCP Scopes and zones are the same.

You don't need a DHCP relay on every hop, just one DHCP Relay on everyVLAN where you want to serve DHCP IPs.

Example:
VLAN 5: Users, Router IP: 10.0.1.1, DHCP helper enabled.
VLAN 6: Users, Router IP: 10.0.2.1, DHCP helper enabled.
VLAN 7: Firewall, WAN.
VLAN 8: Servers. DHCP Server IP 10.0.25.3.

You need to configure DHCP helper on VLAN 5 an 6 so the Users will be able to get an IP. The helper must be configured to send the requests to DHCP Server (Ip 10.0.25.3).

The Firewall on VLAN 7 does not need any DHCP helper as there are no users on that VLAN. It just need to allow the DHCP Relay traffic to pass from VLANS 5 and 6 to VLAN 8.

The DHCP Server will get the requests from VLAN 5 and 6. It will also get the IP from the router which has relayed the request. When the request is comming from the router with IP 10.0.1.1 it will serve IPs from the range 10.0.1.1-10.0.1.255, when relayed from router with IP 10.0.2.1 it will serve ips from range 10.0.2.x

 

by: 53tinPosted on 2009-06-22 at 04:49:57ID: 24681471

Okay, so I know my checkpoint has DHCP relay set up on VLAN 37, and my server has the correct scope installed in it for that VLAN. However, whenever I plug into a known good working VLAN 37 switchport, I am unable to get an IP. The switchport is configured for VLAN 37, while my server is on VLAN 45, which is a different subnet mask; does that matter, is the server unable to hand out the correct IP because of that? the subnet is configured in the scope correctly, so I was assuming it would handle the addressing accordingly, but I might have been mistaken on that. I also enabled DHCP snooping on my 4507 core switch and wasn't seeing any DHCP requests coming in when I know my laptop is trying to get an IP. I'm just wanting to make sure that neither the switch I plugged my laptop into, the 6509 layer 3 switch, or the 4507 core switch could be stopping the request. Any ideas on where to start looking? Thanks for all the help so far, I hope it isn't a simple mistake I'm missing....

 

by: sorrilloPosted on 2009-06-22 at 11:03:12ID: 24684909

The checkponint that acts as DHCP relay is also on VLAN 37 ? (it should as it must be able to listen for DHCP requests on this VLAN).

It does not matter that VLAN 37 and VLAN 47 are on different subnets and with different mask.

I think I can not help you any further as I don't know much about cisco specifics. Maybe someone els can help you on the commands and configurations for those models.

 

by: grsteedPosted on 2009-06-22 at 16:39:03ID: 24687648

You do need to make sure the traffic can route back from the Server to the DHCP client network. This is normally accomplished through normal routing on the Router. It usually knows about all of the networks through a routing protocol such as OSPF, EIGRP, or RIP. To test this, log on to the DHCP server and try to ping an IP address on the client network. If it fails doing a traceroute (tracert w.x.y.z) may tell you where it stops, although some devices don't respond to ICMP.

Another possibility is the default gateway on the server point to a different router that doesn't know about the DHCP client network. This may happen if the server is multi-homed. To work around this problem a static route is required on the server that can route the traffic to the client network.
 
This is from route ? on the command line.

> route ADD 157.0.0.0 MASK 255.0.0.0  157.55.80.1 METRIC 3 IF 2
         destination^      ^mask      ^gateway     metric^    ^
                                                                                        Interface^

You want to make sure you use the -p option to make it persistent otherwise it will be lost when you reboot.

Cheers,
Gary

20120131-EE-VQP-002

3 Ways to Join

30-Day Free Trial

The Experts

98% positive feedback on 31,087 answers since March 2000. angeliii is a Microsoft Most Valuable Professional for his work with MS SQL Server & Develoment.

He has also proven his knowledge of Visual Basic Programming, PHP Scripting and Oracle Databases.

The Experts

97% positive feedback on 10,752 answers since July 2000. lrmoore has more than 18 years experience in the networking industry.

The six-time Mircosoft MVPs specialties include firewalls, virtual private networking, and network management.

Testimonials

"...and excellent source for support... Kind of like having your very own IT dept." Electriciansnet

Testimonials

"I was apprehensive at signing up at first. However... it has already made my life as an IT administrator much easier." JaCrews

Testimonials

"WOW! You guys have great, active, and knowledgeable people on here." moore50

Business Clients

Business Clients

In the Press

"If you’ve got a question... Experts Exchange can supply an answer.”

In the Press

"...an invaluable aid for both IT professionals and those who require tech support."

In the Press

"where IT professionals provide quick answers on just about any topic"

Business Account Plans

Loading Advertisement...