Flexconnect - Local Switching and DHCP Server Location

[snarayanaraju]

Hello Friends, It is again a conceptual question.

In Flex-connect Local Switching mode if the Client has to be get the IP address using DHCP, the DHCP server has to be local to the remote site and not centralized location. Though i know, Local switching means that the client traffic is bridged to the local network directly by the AP on the locally connected switch and does not pass through the controller, what does it mean to DHCP server location.

For example, If I have 2 different WLANs (VLAN 2 and VLAN 3) configured Local Switching and its corresponding VLAN SVIs are configured in the Local L3 Switch and if the DHCP server is centrally located with the scopes for VLAN 2 and VLAN 3, will it have troubles?

I see in my infrastructure we are working in that way [Local switching with centralized server]

Thanks in advance

SAIRAM

[Viten Patel]

Hi Sairam,

yes you will have trouble. if you want to use local switching then its a good idea to have the DHCP server at the local site.

[George Stefanick]

Piggy backing on Viten comment, BTW +5 Viten on your response! 

The point of flex is to allow your location to be "autonomous". In other words, keep the local office as a standalone incase of failure and also keep the traffic local. Where this normality goes sideways is when you do dot1x and have a radius server or AD requirements at the central office. 

I agree -- keep DHCP local. 

[snarayanaraju]

Thank George, Viten - I accept you and Cisco document says DHCP server should be local to Site in Flex-Connect environment. But i am looking for a deep insight what would be the practical problem when having a Centralized DHCP Server. I know it technically works because one of my retail client is having a centralized DHCP server for wireless network configured in FlexConnect.

Sorry for my late response as i was away from office for all these days

Thanks and regards,

SAIRAM

[George Stefanick · Accepted solution]

Lets take a step back and talk about the purpose of Flex connect. FC was design for the purpose of providing wireless connectivity to remote locations, where you did not have to install a WLC each time. As you know the WLC really is used for management once the FC ap is set upm unless  you are doing EAP or something fancy.

With that said. You have a remote office with 10 FC aps. You are pulling DHCP centrally. Now you have a dependency if you lose that link, DHCP. Some customers who deploy FC do so with a design that doesn't require central dependency. 

Say the link fails .. Your wireless clients that have DHCP will work as normal or until the lease is up. New clients won't connect. 

Make sense?

[snarayanaraju]

Thank you. So i understand in FC environment centralized DHCP is technically feasible but as best recommended practice we don't. Correct?

[Moin Ilyas]

It would be good to have DHCP server at local site.

Please refer to the following link for more details.

http://www.cisco.com/c/en/us/td/docs/wireless/controller/7-6/configuration-guide/b_cg76/b_cg76_chapter_010001000.html#ID17