03-19-2012 01:45 PM
I have a 3600 controller running 188.8.131.52 with about 200 remote aps configured with split tunnel. Over the weekend I noticed about 4 GB of data getting transferred between the controller and about 20 remote APs. All of the 4GB of traffic was from udp 4500. Does anyone know why so much traffic is getting generated? And what that udp 4500 is actually doing? I understand that is what nat traversal uses for setting up gre tunnels but why is each of the 20 remote ap transferring about 100-400 MB of data?
03-19-2012 01:53 PM
All of the traffic to those sites, whether it is data or management traverses that tunnel.
To minimize the traffic, you could:
- Suppresss Broadcast traffic on wireless (config t wlan virtual ap <vap> broadcast filter all)
- Suppress Broadcast traffic on the wired interface of the RAP by enabling bcmc-optimization on the VLAN interface (config t interface vlan 10 bcmc-optimization)
Suppressing broadcasts on the VLAN interface also suppresses broadcasts on the wireless, as well.
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03-19-2012 01:59 PM
I don't see that much traffic during the weekdays, and not even during the weekend sometimes. It seems to generate that traffic whenever a remote ap loses connectivity. Does it have to transfer all of the configs each time it has to reestablish the tunnel?
03-19-2012 05:43 PM
Are all (200) the RAPs in the same AP-Group?
How many VAPs are being used and what are the VLANs configured?
Are you using wired-port on the RAP? If so what VLAN?
Do you see RAPs reboot/bootstrap when issue happens?
03-19-2012 11:02 PM
broadcast filter all (on a per VAP basis) and bc-mc optmization (on a per VLAN basis) helps with reducing broadcast/multicast traffic. However, the ARP traffic is not filtered by the bc-mc optmization and the ARP traffic can cuase such huge spikes in bandwidth consumption. Using smaller VLANs will help to drastically reduce the ARP traffic. A VLAN with 60-80 (100 devices max) is a good number.This will increase the number of AP groups but will reduce the arp traffic drastically. You can also use the ip--local-proxy arp on a per VLAN basis to reduce the arp traffic.
(MC1-Sunnyvale-3600) (config) #interface vlan 130
(MC1-Sunnyvale-3600) (config-subif)#ip local-proxy-arp