Wireless Access

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?

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

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?

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 ?

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?

Mr. Wind,

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

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.

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.

I'm running 6.4.2.5 on my controlers.

So multicast across VLANs would work with BC/MC optimization enabled and igmp snooping?

I usualy configure igmp proxy on the interface vlan but I've also disable it on the VLANs I'm using for multicast.

Yes. Here is how it works:

• AOS 6.4.1+
• If "broadcast filter-all" parameter is enabled, the controller will allow multicast packets to be forwarded if:
• Packets originating from the wired side with destination range of 225.0.0.0 - 239.255.255.255 AND
• A station has subscribed to a multicast group
• If IGMP snooping / proxy is disabled, the controller will not be aware of the iGMP membership and drops the multicast flows
• If DMO is enabled, the packets will be sent with 802.11 unicast headers
• If Airgroup is enabled, mDNS/SSDP packets are sent to the Airgroup application.

I just tested with ip igmp snooping on 2 VLANs:

Before setup :  VAP with vlan pool of 2 vlans, DMO enabled, supress-arp enabled and supress-all disabled, on both interface vlan I've put an IP adresse and enabled local-proxy-arp. Works on both VLANs

Tested :

IGMP snooping with DMO > breaks multicast across VLANs

IGMP snooping without DMO > works across VLANs

IGMP snooping without DMO + broadcast filter-all > breaks all client discovery

IGMP snooping without DMO + bc/mc-optimization > beaks all clients discovery

IGMP proxy without DMO + broadcast filter-all > breaks all client discovery

Everyone is connecting on the wireless

I have 1 teacher laptop (sending multicast to discover student clients) connecting on vlan 1

I have 2 student clients, one connecting on vlan 1 and the other on vlan 2

Does the multicast really need to be originating from the wired side ?