Wireless Access

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Contributor I

Large subnet on wifi - broadcast domain impact

Hi,

 

For various reason, we'll be changing our IP subnet on the wireless. We want to have a dedicated IP subnet by building as we already have on the wire side.

 

We have at the peak about 500 concurents clients per building, to be future-proof we would like to have 2000 IP adresse available by building, requiring a /21 subnet.

 

Our problem is that some building require to have broadcast and multicast enable to support an application (LanSchool).

How big would be the impact on the performance compare to our current setup of vlan pooling of /24 subnet? Is there a better solution ? Could Airgroup be adapted to support the multicast of LanSchool ?

 

I guess the real question would be: how big can I make a IP subnet with BC/MC enabled before the performance impact become too big?

Guru Elite

Re: Large subnet on wifi - broadcast domain impact

There are many Aruba customers running a single /16 with BC/MC enabled.

 

 


Tim Cappalli | Aruba Security TME
@timcappalli | timcappalli.me | ACMX #367 / ACCX #480
Contributor I

Re: Large subnet on wifi - broadcast domain impact

Wow, that big with BM/MC enabled ?

 

Do you take any special mesure/configuration to mitigate the performance impact? Or the impact just is negligable enought that the clients don't complain of low performance?

Guru Elite

Re: Large subnet on wifi - broadcast domain impact

The performance with drop BC/MC should be very similar to a smaller subnet.

Tim Cappalli | Aruba Security TME
@timcappalli | timcappalli.me | ACMX #367 / ACCX #480
Contributor I

Re: Large subnet on wifi - broadcast domain impact

I've always thought that the more users you have in a subnet the more you would have ARP and others broadcast packets going in the network. Knowing broadcast slow down wireless networks wouldn't that increased number of users cause slowdown ?

Guru Elite

Re: Large subnet on wifi - broadcast domain impact

That is all taken care of with the bc/mc optimizations.

Thanks,
Tim

Tim Cappalli | Aruba Security TME
@timcappalli | timcappalli.me | ACMX #367 / ACCX #480
Contributor I

Re: Large subnet on wifi - broadcast domain impact

Great ! I've already enabled that option but i'm unsure if i've configured the right threshold.

 

Right now the threshold i configured is 100 of the 255 limit, there about 120 clients on average connected to that SSID, they might not be all using the multicast based program (lanschool).

 

Is this threshold too high ? How do you configure it?

Guru Elite

Re: Large subnet on wifi - broadcast domain impact

Mr. Wind,

 

What parameter are you configuring?  BCMC optimization only has an on/off...



Colin Joseph
Aruba Customer Engineering

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Contributor I

Re: Large subnet on wifi - broadcast domain impact

I was confusing BC/MC optimization to DMO.

 

We cannot enable BC/MC optimization as we need to support lanschool to go on multiple vlans (clients on wired and wireless), enabling BC/MC optimization breaks that.

 

The only setting that doesn't break any Lanschool functionnality is Dynamic Multicast optimization, witch has a configurated threshold.

 

Broadcast-AP Group.png

Guru Elite

Re: Large subnet on wifi - broadcast domain impact

What version of code?

 

Multicast can still work with BC/MC opt enabled but you need to be sure IGMP snooping is enabled on the controller.


Tim Cappalli | Aruba Security TME
@timcappalli | timcappalli.me | ACMX #367 / ACCX #480
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