What benefit dhcp option 43 can provide

[eigrpy]

Document states DHCP option 43 helps AP to associate with the WLC in another subnet network. Since APs are configured with  static ip address and WLC ip address, why these APs need option 43? In real network, APs also can work well with WLC in different subnet without the option 43. So I would like to know what benefit the option 43 can provide in joining wlc or get ip address? Thank you

[marce1000]

 - Normally AP's use DHCP and then option 43 is needed for them to get the info for the controller-address. DHCP is better, why -> things become more manageable when infrastructure changes, more flexible to add ap's and more

 M.

[eigrpy]

Thank you for your reply. 

So we do not need to use option 43 if using static ip address for ap and wlc in this ap? even option 60?

[marce1000]

 >So we do not need to use option 43 ...

    No because when static ip is being used , the DHCP server is not contacted and no option 43 can be provided, I guess then the AP needs manual configuration on the WLC, one more argument for using DHCP.

 M.

[marce1000]

 - Small correction (as Scott was saying) :

           When an AP has static ip it contacts the DNS to resolve CISCO-CAPWAP-CONTROLLER.localdomain. When the DNS sends a list of controller IP addresses, the AP sends discovery requests to the controllers.

 M.

[Scott Fella]

Option 43 and or DNS are only required for initial discovery.  You don't need it unless you are adding more ap's and your ap's are not on the same subnet as the controller management.  So these are options folks use depending on what they want to do.  Just like static address or initial ap staging from the console, this is optional.  You just need to understand the ap join process and then assess the risk in case your ap's drop off or maybe need to get replaced.

[eigrpy]

" You don't need it unless you are adding more ap's and your ap's are not on the same subnet as the controller management. .."

In this situation that you mentioned, if These APs have static ip address for itself and its WLC, is it necessary for these APS have option43? Thanks

[Scott Fella]

If your ap's are already joined, then you do not.  As long as you know how to join an ap to a controller, then you don't need any of these options as its options and not required.

[Leo Laohoo]

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@eigrpy wrote:

So I would like to know what benefit the option 43 can provide in joining wlc or get ip address?

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The main benefit of DHCP Option 43 is allow the quick provisioning of (a mass of) APs.  

Even if the APs will be configured for static IP address, if there is a large amount of APs to do, DHCP Option 43 is the fastest and most effective method.  

It is very rare to see anyone manually configure static IP address because it is very easy to "s_crew things up" with static IP addresses.  A good example are: 

1. Manually configuring the static IP addresses, subnet mask and default gateway can risk "fat finger". 
2. What happens if the subnet needs to be changed. 
3. Behaviour of the network which can cause the AP to "throw out" the static IP address.