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Cisco Router Local DHCP Server VS. DHCP Relay (Helper Address)

I currently have a VLAN that will require DHCP.  I am attempting to decide between serving DHCP from the router locally, or using DHCP relay to send the request to our DHCP server.  Unfortunately, after searching the forums and online, I've been unable to find an answer to my question, so I'm posting here.

It seems my 2 choices are:

***configure DHCP relay***

service dhcp

interface FastEthernet0/0.2

ip helper-address XXX.16.10.100

***Configure 2008 multi-scope DHCP***

http://technet.microsoft.com/en-us/library/dd296698%28v=WS.10%29.aspx

OR

***Configure DHCP server***

ip dhcp pool m105

network XXX.1.105.0 255.255.255.0

domain-name XXX

dns-server XXX.8.8.8

default-router XXX.1.105.1

ip dhcp excluded-address XXX.1.105.1 XXX.1.105.9

We only have 2 VLANs today, and the DHCP server is live on one of them.   In the future we may have several more VLANs, all requiring DHCP at some point.  Perhaps there will be a large portion of DHCP static reservations depending on the VLAN's purpose.

My Questions:

Is there an objective way to determine which method I should implement?

And:

If there is no facts-based method, what are your suggestions?

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Cisco Router Local DHCP Server VS. DHCP Relay (Helper Address)

Hello,

Strictly speaking with the current setup of 2 vlans, it should not be taxing for the router to handle it. However we must understand that the router handles DHCP functions in software, which means the CPU needs to handle everything, from keeping a tab of address leases to new address assignation. Obviously, as the network grows, you would be moving the router into a contentious position where it would obviously have other duties to perform, apart from just DHCP. I would rather suggest having the DHCP server on an external server, and using the relay agent functionality.

Obviously enough, this is a subjective question, since a lot depends on the network requirements, and I would leave the forum open for further suggestions.

HTH

Pronoy

3 REPLIES
Cisco Employee

Cisco Router Local DHCP Server VS. DHCP Relay (Helper Address)

Hello,

Strictly speaking with the current setup of 2 vlans, it should not be taxing for the router to handle it. However we must understand that the router handles DHCP functions in software, which means the CPU needs to handle everything, from keeping a tab of address leases to new address assignation. Obviously, as the network grows, you would be moving the router into a contentious position where it would obviously have other duties to perform, apart from just DHCP. I would rather suggest having the DHCP server on an external server, and using the relay agent functionality.

Obviously enough, this is a subjective question, since a lot depends on the network requirements, and I would leave the forum open for further suggestions.

HTH

Pronoy

New Member

Cisco Router Local DHCP Server VS. DHCP Relay (Helper Address)

Thanks for the information.  It really seems like the benefits of each approach depends on the scale of our use of VLANs.  Thanks!

New Member

Cisco Router Local DHCP Server VS. DHCP Relay (Helper Address)

Hello!

Is there any official document that describes recommendations for moving DHCP server from Cisco platforms to hardware server depending on DHCP clients number? How many dhcp bindings or pool numbers can VSS Supervisor 720 handle without switching impact?

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