IOS DHCP-Server use defined range

[whistleblower14]

Hi,

I`ve a question about the IOS DHCP-Server... what is the difference between the usage of command ip dhcp excluded-address vs. ip dhcp class // address range? Is there any advantage or disadvantage and when should one or the other be used?!

[e.ciollaro]

Hi

ip dhcp excluded-address is intended to define which ip addresses in subnet can't be assigned via DHCP protocol to any host (ie defining a reserved set of IP) 

while dhcp class is a method to group DHCP clients based on some shared characteristics other than the subnet in which the clients reside, it has nothing to do with usable or reserved ip address.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr/command/ipaddr-cr-book/ipaddr-i1.html#wp3015696029

and

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_dhcp/configuration/15-mt/dhcp-15-mt-book/config-dhcp-server.html

[whistleblower14]

@e.ciollaro thank you for your Response on this! Under the second Link you`ve mentioned there`s a great explantion about the function!

but please let me ask you a question about the following configuration. what would you say about this? it`s from a switch which has a customer in use does that configuration make sense in your opinion? Because I`m not able to figure out the need of that or the difference to excluded IP-Adresses...

ip dhcp class CLA-LIMIT
 remark limit Address Scope
!
ip dhcp pool DHCP0403
 vrf ik0403
 network 10.4.3.0 255.255.255.0
 default-router 10.4.3.254
 dns-server 10.1.1.11 10.1.1.12
 class CLA-LIMIT
  address range 10.4.3.11 10.4.3.200

[Deepak Kumar]

Hi,

https://blog.ine.com/2009/07/22/understanding-dhcp-option-82

It will explain you bit more.

Regards,

Deepak Kumar

[whistleblower14]

hi @Deepak Kumar 

I have read through the post, but I still cannot find a meaningfulness for the configuration I mentioned? In the configured ip dhcp class is execpt for a remark entry no other parameter/sub-Options configured?!

[Georg Pauwen]

Hello,

with just the address range in the class, the functionality is exactly the same as with the ip dhcp excluded command. It seems to me that the class might be configured for admnistrative purposes, because you can add a remark, somehing you cannot do with the ip dhcp excluded command.

[Deepak Kumar]

Hi @Georg Pauwen 

It seems something different. 

(Optional) Sets an address range for the DHCP class in a DHCP server address pool.

If this command is not configured for a class, the default value is the entire subnet of the pool. Each class in the DHCP pool is examined for a match in the order configured.

I will read the complete guide and come back.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_dhcp/configuration/xe-3se/3850/dhcp-xe-3se-3850-book/config-dhcp-server.html

Section: Defining the DHCP Address Pool