WLC Multi-Interface WLAN with static IP or DHCP reservations

[Wes Schochet]

We are in a hospital environment are are constantly running up against size limits on SSIDs.  The new Interface group feature seems like the perfect solution for our problem.  I do however have some devices on these SSIDs that have either a static IP address or a reserved IP based on their MAC address that gets assigned from DHCP.  

I remember reading somewhere about the vlan / subnet allocation scheme, but I can't find it. I am concerned about the interaction here.  Is it possible that all devices are assigned to the first vlan / interface and only look for a second one if DHCP is full?  that seems too good to be true.   

Any ideas or suggestions would be appreciated!

[Stephen Rodriguez]

The devices are assigned a MAC hash that's get stored on the WLC.  Addresses are issued in a round-robin approach from all the interfaces in the group.

• If a client has a static IP configured in, for example, subnet A, and they are allotted subnet B, they will get moved to subnet A (override), before moving to the RUN state, if these conditions are met:

  • DHCP Required is disabled on the WLAN.

  • Subnet A is included in the VLAN or the AP group is configured on the WLAN.

  • The client sends some packet sourced with a static IP in subnet A within the DHCP_REQD interval (~ 2 min default value).

• The DHCP_required interval is configurable and can have a maximum value of 120 seconds. Go to Controller > Advanced > DHCP Parameters > DHCP timeout (5-120 seconds).

• If the static IP client has an IP address from a subnet that is part  of the interface group which is mapped to the WLAN, then the static IP  client that joins over that WLAN will move to a RUN state and can pass  traffic. Otherwise, the static IP client cannot pass traffic.

http://www.cisco.com/en/US/products/ps10315/products_tech_note09186a0080bb4900.shtml

HTH,
Steve

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[Wes Schochet]

Thanks so much - this is exactly what I was looking for!