A few of you have asked about measures that we have taken to "control broadcast". Here is a list:
First, some numbers: We have today beween 20 and 60 packets per second of Broadcast/Multicast, this is for a subnet that has 950+ APs and up to 3000 concurrent users and growing, one layer 2 domain. Our other subnets have 250 APs, 50 APs, and a bunch of smaller ones. A vague indicator of quality of service could be: I can do SKYPE in most places with a good quality of communication! Most of our users use laptops, not too many PDAs. It has been mentioned that devices with less potent CPUs have a harder time to deal with big broadcast traffic. (our Cisco SE likes to remind me about that. Is it to sell a LWAPP system, or is it a fact?) What can be done to limit broadcast: -Use one contiguous IP range for the VLAN (avoid secondaries) (the more subnets the more ARP requests) -Isolate the management of APs on a different VLAN (IAPP is extremely verbose. It's also a good security measure) -Enable Proxy ARP on APs (this is vendor specific unfortunately) Instead of propagating arp requests to the air, the AP replies on behalf of clients just for ARP requests, leaving ARP to the wired side of the network -Broadcast and Multicast Storm treshold (also vendor specific) can be tuned up to 1 packet/second -Enable P-node in WINS server, which limits Netbios traffic -If you cannot do P-node, filter Netbios on the AP or on the switch port (limiting Netbios to one AP only)...your users won't like it, though. -Block IPX (amazing the amount of machines that still do IPX) -On the Multicast side: ...we are still debating about enabling Multicast on AP ports (if you have some input on this please share it!) -Divide and conquer: you can keep a large layer 2 domain and subdivide it in multiple SSIDs/VlAN/Subnets. Our visitor network, 802.1x network and Web-reg network are all separated as far as layer 3 is concerned, but all have parallel layer2 domains. I call this Vertical subnetting. Everytime we considered chopping our layer2 domain (in this case it would be Horizontal subnetting) in smaller subnets we noticed that buildings were too close to each other and people may roam to other subnets just by being closer to a window, generating unwanted IP problems. If you have other measures that one can use to reduce Broadcast, please share with the list. Thanks, Philippe Hanset University of Tennessee On Mon, 11 Sep 2006, Daniel Eklund wrote: > On Sep 10, 2006, at 3:35 PM, Philippe Hanset wrote: > > >> Putting all the APs in the same L2 domain has been done before, > >> and I would > >> only recommend it for the smallest deployments. Broadcast > >> traffic, on the > >> wireless and the wireline side, will absolutely ruin performance, > >> as you > >> pointed out, can cause AP issues. As you pointed out, the L3 roaming > >> concern prevents you from segmenting the APs as you wish. > > > > Small domain? > > We have about 950 AP in one subnet with sometimes 3000 concurrent > > users > > and it works great. We did take some measures to prevent unwanted > > broadcast traffic though. > > Philippe, > > What specific things have you done to reduce broadcasts. > > ********** > Participation and subscription information for this EDUCAUSE Constituent > Group discussion list can be found at http://www.educause.edu/groups/. > ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.
