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Wireless 5508 WLC's in a Mobility Group


Scenario: Would like redundancy on 2 x 5508's but unable to utilise HA (SSO) due to internal WLC DHCP requirements.

Mobility groups - Can 2 controllers in the same mobility group share a DHCP scope? I.E overlapping addresses or would the scope need to be split across controllers?

If scopes are slit hat happens to DHCP requests once the primary DHCP server has allocated all leases? Also what happens if a clients joined controller A receives valid IP address then controller A goes off line? AP's re-establish with controller B but client has invalid scope IP?







 DHCP isn't shared between


DHCP isn't shared between controllers. If you want to share scopes you can split the start and end range between them .. Ive done this before and it works well. We split guest scopes this way. It works. 

DHCP isn't trivial. Its simply an address given to a device. If a device gets an IP from controller A and it goes down and the AP moves over to controller B the client will shift with it. If the client lost connection and required to reIP then it would get a new IP from the new controller. 



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Hi George,Thanks for your

Hi George,

Thanks for your reply.

I'm using vlan select interface groups utilising several /24 networks for a large DHCP pool for one WLAN. How are clients assigned IP addresses? Is this random or is it round robin type algorithm?

what happens when scopes on WLC A are exhausted? 

round robin 

round robin 


Hi,1. Yes, DHCP use round


1. Yes, DHCP use round robin type algorithm, it never give the IP address in random order.

2. When address scope is exhausted that WLC wouldn't allow to further client to join the network.

if you have more than 250 user per scope then you configure /16 subnet on it.


Hi Abwahid.I'm not sure if

Hi Abwahid.

I'm not sure if /16 is the best subnet. 

Maybe /22


Hi,Actually in the Mobility


Actually in the Mobility Group you enable the user to move form one WLC APs coverage to other WLC APs coverage with same client IP configuration.. so if we  make groups then obviously we should make different DHCP scope to avoid network address range exhausted.

As far as controller A is up, IP configuration on wireless client would be remain same, but if your controller A goes off then the client will acquire the new IP from different DHCP scope which is assigned to controller B.


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