DHCP on CISCO routers

[SCLDTony]

I am looking for opinions and/or experiences in using the DHCP tools in CISCO IOS. We are a 10 site Win 2K/Active Directory network. We are a star topology. We have Cisco 2600 series routers at all of our remote sites and a 3640 at "headquarters". We are using private addressing (10.0.0.0) and the EIGRP routing protocol.

I would like to use the DHCP feature on the routers rather than adding another function to our MS Win 2K servers. I would like to create a new subnet at each site (ie 10.100.0.0, 10.110.0.0, 10.120.0.0, etc)and have each router in that subnet serve DHCP to the hundred or so nodes at that site.

Has anyone done this or see any pro's or con's in doing so. I am open to any suggestions or comments, thanks in advance for all your help!

Tony LaSoya
tlasoya@scld.org

 

[chelenegro]

- I've run DHCP in almost all the Cisco platforms so far. I can confirm its stability. You will have to configure the dynamic pool for each range, and then the appropriate options, lease, netbios, dns servers, gateway, etc...
- Plus you can easily exclude certain ranges from within the pool, and create static ip entries as well.
- Another one interesting is the memory allocation requirements:
Memory Requirements. RAM requirements can be estimated with the following formula:
RAM = (40K for global variables, processes, etc.) +
(112 * number of database agents) +
(292 * number of address pools) +
(280 * number of pool parameters) +
(104 * number of addresses available for assignment)
If your familiar with Cisco CPU numbers, you'll see that even the largest DHCP configs will probably not require a lot of processing from the router.
- You can setup a database agent for the router to store the dynamic bindings as well, in case it reboots or crashes. The static bindings are stored in the NVRAM so they will be there if the router reboots.
- Cisco has a very good and complete documentation on the topic. I suggest you visit the site and look for it

Hope it helps,
Jose Luis

Jose Luis Martin Cenjor
HP Global Technology Solutions

http://www.hp.com

 

[SCLDTony]

Jose,

Thanks for the great information. I thought I was on the right track, thank you for confirming it. I do have another question, how do I assign a range for each individual software vlan? Is that even possible? Thanks again for your assistance.

Tony LaSoya
Spokane County Library District
(former HP Vancouver employee )

 

[chelenegro]

Tony,

No problem at all former HP Vancouver . You just have to configure the appropriate dynamic IP range for each of those vlan pools you create. The router as bridge between broadcast domains (i.e. vlans) will understand from the client IP from where the DHCP renew/request comes and will bind that client with the appropriate DHCP settings and IP.
Keep me informed on how it works ...


Jose Luis Martin Cenjor
HP Global Technology Solutions

http://www.hp.com

 

[skotman]

Tony,
Check out:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t1/easyip2.htm

That is cisco's manual for DHCP with their IOS. I've used it before (I swear by DHCP to begin with) but cisco made it fairly easy if your familier with the IOS CLI. Good luck!

Scott Heath

http://www.scottspad.com

AIM: orange7288

 

[SCLDTony]

Thanks to both of you... the CISCO document is where I started with all of this and it is good information. I have not tried the vlan setup yet (still working on how to set a physical vlan on a switch tied to the software vlan on the router... does CISCO have a document for THAT?). I appreciate your suggestions and will surely have some more questions on a few days...

Tony

 

[ilpadrino]

good thread, would this be achievable using instead one of your win2k server as dhcp -- that is with the different subnets?

or do you prefer to use cisco ios?

what would be the minimum requirements for the hardware in the routers? i have less than the 2600 you've mentioned at my remote sites.

 

[chelenegro]

ilpadrino,
I'm not a W2K expert but from what I know W2K can run DHCP service normally so you could certainly achieve all mentioned above under that platform.
You can refer to Cisco.com for a more detailed list of platforms ... but here a snapshot:
• Catalyst 5000 family switches with an installed Route Switch Module
• Catalyst 6000 family switches with an installed Multilayer Switch Feature Card
• Catalyst 8500 series
• Cisco 800 series
• Cisco 1000 series
• Cisco 1400 series
• Cisco 1600 series
• Cisco 1700 series (support for the Cisco 1700 series was added in Cisco IOS Release 12.0[2]T)
• Cisco 2500 series
• Cisco 2600 series
• Cisco 3600 series
• Cisco 3800 series
• Cisco MC3810 series
• Cisco 4000 series
• Cisco AS5100 access server
• Cisco AS5200 universal access server
• Cisco AS5300 universal access server
• Cisco 7000 series
• Cisco 7100 series
• Cisco 7200 series
• Cisco MGX 8800 with an installed Route Processor Module
• Cisco 12000 series
• Cisco uBR900 series
• Cisco uBR7200 series
As I said before, Cisco IOS DHCP has proven to be a pretty stable and easily configurable feature. I advice it.

Jose Luis Martin Cenjor, CCNA, CCNP
HP Global Technology Solutions

http://www.hp.com