Wireless Access

We had an issue tonight with the Master controller sending so much traffic to the AP's that it fully saturated our WAN.  At one point the interface utilization almost hit 100MBps at 11:00PM with very few users.  On a normal day full of users it doesnt pass 15MBps.  I called tac and after working on this for some time we enabled bcmc-optimization and saw the traffic decrease to normal levels.  They noticed on the output below that ARP was incrementing quickly on line 5.  After BCMC was applied it did not increment.  I am glad it appears to be fixed but I am concerned where this issue came from.  This config has run for years without issue.  Has anyone else heard of or experienced similar issues?

(BF-ARUBA-3600) #show datapath bwm

Datapath Bandwidth Management Table Entries
-------------------------------------------
Contract Types :
   0 - CP Dos 1 - Configured contracts 2 - Internal contracts
-----------------------------------------------
Flags: Q - No drop, P - No shape(Only Policed),
       T - Auto tuned
---  --------  ---------  ----------  -----------  -----------------
     Cont                       Avail   Queued/Pkts
Type  Id   Bits/sec  Policed    Bytes    Bytes      Flags
---- ---- --------- ---------- ------- ------------ -----
0    1     20000000          0   78125       0/0
0    2      4000000          0   15625       0/0
0    3    160000000          0  623399       0/0
0    4      4000000          0   15625       0/0
0    5      2000128  187376649    7813       0/0
0    6      2000128          0    7813       0/0
0    7      2000128          0    7813       0/0
1    1       384000          0    1500       0/0

Even 4 megs of multicast traffic can bring a wireless network to its knees if it is replicated to all of your APs.  BCMC optimization stops that on the wired and wireless portions of the AP.  It could have been anything.

Just today, I had a user who only had 20 wired users in the same subnet as the APs and users, but one wired client was doing a HD multicast stream that was punishing all the wireless clients.  It does not take much.

Thanks for the info.  I was suprised that could have such an impact but it sounds like it is not that unusual.  Is this a setting that alot of your customers enable because it seems necessary?  Its interesting because we never ran into it before and tracking it down is dificult without a packet capture.  The issue is any captures we get are encrypted.  Do you know of any other ways to capture or identify the traffic?

Thanks again

From my perspective, I always configure broadcast suppression since most modern enterprise applications are unicast-only, so I do not see it often.  If someone says that their wireless was good and then it got bad, that is the first thing that I do.  If it is affecting clients, no matter what band, that is a strong sign it is NOT interference, but contention.

 The TAC method you show of applying bcmc optimization(to drop broadcasts) and then showing what is policied is a very good way.

Others may want to comment on what they do, as well.

Sorry to bring up this old thread, I am trying to understand the difference of checking BC/MC optimzation and checking Drop Broadcast and multicast” do they do the same thing, should we have both on or just one?

Thanks:)

BCMC Optimization at the VLAN level eliminates the need to enable it at the VAP level.  It will also drop those broadcasts on wired interfaces, like the wired interface of RAPs, where "Drop Broadcasts" at the VAP level have no effect.

Thanks for the quick reply,

We were advised to check 'drop broadcast and multicast ' on the on all of our vap profiles and check BC.MC rate optimization on our SSID profile just for our bridged mode dot1x employee profie (not our gues profile). Do these coexist or should we do one or the other?

Thanks.

bcmc optimization at the VLAN level does what was explained above.

bcmc optimization at the SSID level sends out broadcast/multicast at the rate of the client with the lowest association rate.  Broadcasts and multicasts are normally sent out at the basic rate (1,2 or 6 depending).  BCMC optimization at the SSID level will attempt to send out broadcasts and multicasts at the rate of the client with the lowest association rate.  

If you are dropping broadcasts at the VAP or VLAN level, you will never see those broadcasts or multicast in the air, so it negates BCMC optimization at the SSID level.

Thanks CJOSEPH.