Converged Access Design Help (Catalyst 3850 and WLC 5508...Mobility Oracle)

Question

Hello,
I am an engineer working with a Cisco Gold Partner in Saudi Arabia. We have a large university as our client where they are constructing a new
building and require our services to build the network infrastructure. Therefore, we are to implement the routing and switching infrastructure as
well as the Wireless solution.
At present, I have no issues in implementing the R&S infrastructure as it is very straight forward but it has implications on the deployment of
the wireless solution which I explain further below. The R&S infrastructure comprises of the typical Core, Distribution, and Access layers and we
are focusing on the local distribution and access switches with regards to the new building. The client has a converged Layer 3 network spanning
from distribution layer to core layer and they are running EIGRP for this convergence. This is not a problem and has already been implemented.
Yet, the challenge arises in deploying the WLAN infrastructure. The client already has a Cisco WLAN infrastructure in place where they have a
large number of LAPs that are registered with their controllers in the Data Center. They have two WLC 5508 where one is the Primary and the other
the Secondary. The local distribution switch to which the WLC are connected also is the gateway for the SVIs for the SSIDs that are configured on
the controllers. This means that once the packets from the AP come in to the WLC, they are tagged with the correct VLAN and sent to the directly
connected distribution switch which then routes it into the rest of the Layer 3 network. Interestingly, the WLC 5508 are running AireOS 7.6 and
support the "New Mobility" feature. The two controllers have formed a Mobility Group (MG) between each other.
Now, the new building will have two Catalyst 3850 switches installed where each one has a total of 40 AP licenses pre-installed and activated
i.e. a total of 80 APs can be supported by the two switches. A total of 67 LAPs will be deployed in the new building which can be accommodated
between the two switches and their integrated controller.
Yet, based on my understanding and research about Converged Access is that, ideally, the Catalyst 3850 will only run the Mobility Agent (MA)
feature while a central controller would provide the Mobility Controller (MC) service. unfortunately, there are not enough licenses on the
existing WLC 5508 nor can we migrate the new licenses that will facilitate such a split deployment.
This means that I would need to configure the two Catalyst 3850 as independent MC and form a MG between them. I have done this and tested this
already and the mobility is working fine. But my concern is not about getting the Catalyst 3850 to work as this is simple but rather it is
focused on creating a common Mobility Domain (MD) so that clients can roam from this new building to the rest of the campus while maintaining the
state of their connections to the WLAN infrastructure.
To make things more complicated, since the new building will have its own Layer 3 distribution switch and the Catalyst 3850 switches will connect
to this distribution switch, it means that new VLANs and SVIs need to be created for the SSIDs broadcast in the new building. This means that new
subnets need to be assigned to the SSIDs.
As such, I have the following questions:
Q1) If we create new SVIs for the SSIDs (same SSIDs names will be used in the new building as in the rest of the university campus) this means
that new subnets will be assigned to these SSIDs. Now, I believe I have two options...one is to make the new Catalyst 3850s to be in the same MG
as the existing WLC 5508 which then cater for Layer 3 client roaming or I have to treat this as a totally seperate WLAN network and follow on to
the solution as per the next question. Please advise which is a better option?
Q2) I could create separate MG i.e. the new building Catalyst 3850s can be in one MG and the existing controllers can be in another MG. I can
then have one of the existing WLC 5508 (the primary one) to run the Mobility Oracle (MO) feature so as to create a single Mobility Domain (MD).
Would this facilitate in Layer 3 client roaming and RRM for all the controllers in the same MD?
Q3) If I do create a MD, how is this accomplished in such an environment since the documentation is severely limited in this regard?
Please advise at your earliest. To assist further, I have attached a topology diagram which may aid in explaining the situation with more
clarity. If these things are clarified, I will be better able to wrap my head around the technology and in turn service my clients better.
Regards,
Amir

Answer 1

Hi Amir,
Q1) If we create new SVIs for the SSIDs (same SSIDs names will be used in the new building as in the rest of the university campus) this means that new subnets will be assigned to these SSIDs. Now, I believe I have two options...one is to make the new Catalyst 3850s to be in the same MG as the existing WLC 5508 which then cater for Layer 3 client roaming or I have to treat this as a totally seperate WLAN network and follow on to the solution as per the next question. Please advise which is a better option?
I would configure them in the same mobility group. Also configure same SPG for those two 3850 stacks if users are frequently roaming within these two buildings.
Q2) I could create separate MG i.e. the new building Catalyst 3850s can be in one MG and the existing controllers can be in another MG. I can then have one of the existing WLC 5508 (the primary one) to run the Mobility Oracle (MO) feature so as to create a single Mobility Domain (MD). Would this facilitate in Layer 3 client roaming and RRM for all the controllers in the same MD?
MO is not required (it is only for very large scale deployments)
Q3) If I do create a MD, how is this accomplished in such an environment since the documentation is severely limited in this regard?
Yes, documents are hard to find :(
These notes may be useful to you based on my experience. I am running IOS-XE 3.6.1 in my production.
http://mrncciew.com/2014/05/06/configuring-new-mobility/
http://mrncciew.com/2013/12/14/3850ma-with-5760mc/
HTH
Rasika
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