Broadcast domain consideration in large wireless netowrks

[Majid Jalinousi]

Hi buddies,

Suppose there is a wireless network with single SSID but more than 2000 users in this single SSID.

I want to know if there is any design consideration about that? should we put the clients according to some criteria in different VLAN? you know, because of limiting the broadcast domain?

If there is any documentation about the large wireless network design considerations, I would be so appreciate for any reference.

BR,

[Rasika Nayanajith]

Local Mode AP Deployment

As long as you keep broadcast forwarding disabled on your WLC (by default it should be left disabled), there is no problem of assigning large subnets to wireless. Since feature is disabled one client broadcast will not be heard by other clients (as WLC does not forward). I have /20  subnets (~4K hosts) in my production network.

FlexConnect mode Deployment

Since traffic is locally terminated, I would consider similar standard used in wired network segmentation. I have chosen /23 for my wired network segment sizing. Again that is based on some judgement and not have done intensive testing to verify impact  of broadcast based on the size of the subnet.

HTH

Rasika

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[Majid Jalinousi]

Thanks alot,

If I understand correctly, with disabling broadcast domain tow clients connected in same SSID and therefore same Vlan never can communicate with each other. isn't it?

actually I want to know if tow clients want communicate on the same SSID, how it is possible?

Thanks in advance.

[Rasika Nayanajith · Accepted solution]

By disabling "broadcast forwarding", one wireless client boadcast frame will not be received by another wireless client.

No impact to unicast traffic, your wireless clients will be able to talk to each other.

If you want to control that there is a feature called Peer to Peer blocking.

HTH

Rasika
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[Majid Jalinousi]

So many thanks,

I don't understand it very well, if by default broadcast is off how a client can for the first time find the MAC address of destination client?

And if we say broadcast is disabled means the client can not set the destination MAC to ff:ff:ff:ff:ff:ff?

Thanks in advance,

BR

[patoberli · Accepted solution]

The client will do the broadcast and the controller (not sure which one it chooses) will either forward the frame to the specific client (the controller knows every online client) or the controller will directly answer to the requesting client.

The default disabled function "broadcast forwarding" doesn't block your client from sending a broadcast, the controller simply will not forward it to every client, as there is no need to. You still get the answer from an ARP, but I think it's sent by the controller itself.

I think you mean ARP broadcast here, right?

[Daniel Ordóñez Flores]

The WLC has a client data base, and it contains the access point which the client is attached, so if you trying to reach one client and it is connected the WLC will know where forward the Traffic.

[ajc]

Hi Rasika,

I have a quick question, how the WLC manages GARP, what I have seen in another post is that those packets are sent to all the clients in the same WLC no matter if the Broadcast Forwarding is disabled. Any comment is appreciated.

thanks

[sisentner]

Sorry for commenting on an old post but I am very interested in this subject.  I understand that broadcast traffic is not passed by the WLC but in our situation we have centralized WLC's.  We keep the WLC's in data centers and have hundreds of sites that have AP's in local mode, hence CAPWAP all traffic to the WLC's via our fiber network.  All sites have their own L3 networks with a router at reach site.  Here is the foggy part for me.  Is all of the broadcast traffic at sites only blocked only at the WLC or will the local router block that CAPWAP'd broadcast traffic.  I am hoping that I can use a /21 to serve all clients on one WLAN.  We do use Flex in some case's but it doesn't apply to the situation I am curious about.

thanks in advance

[ANTONIO DEUS]

Hello,
I have the almost the same problem.

Thank you.