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CAPWAP bandwidth formula

The following section provides information on how to calculate the control plane CAPWAP traffic load in local bridging. The formula provided can help estimate the approximate package bandwidth cost. This is important for knowing precisely how much bandwidth is required on a WAN link for a centralized ForitGate managing hundreds of access points.

There are multiple factors that might affect the volume of CAPWAP control traffic, including the number of stations there are and large WiFi events.

The Ethernet/IP/UDP/CAPWAP uplink header cost should be approximately 66 bytes.

The tables below depict basic and commonly used optional CAPWAP bandwidth costs, on a per-AP basis.

Note the following:

  • STA: The number of stations associated with the FortiAP.
  • ARP scan: Finds hidden devices in your network.
  • VAP: The number of VAPS held by the FortiAP.
  • Radio: The number of radios (maximum of two) enabled by the FortiAP.
Basic per-AP CAPWAP bandwidth costs
Content Time (seconds) Payload (byte) Package bandwidth cost (bps)
Echo Req 30 16 (66+16)*8/30=21.86
STA scan 30 25+20*sta (66+25+20*sta)*8/30=24.26+5.3*sta
ARP scan 30 25+18*sta (66+25+18*sta)*8/30=24.26+4.8*sta
STA CAP 30 25+19*sta (66+25+19*sta)*8/30=24.26+5.1*sta
STA stats 1 25+41*sta (66+25+41*sta)*8/1=728.0+328.0*sta
VAP stats 15 40+18*vap (66+40+18*vap)*8/15=56.53+9.6*vap
Radio stats 15 25+25*radio (66+25+25*radio)*8/15=48.53+13.3*radio
Total: 908.7+343.2*sta+9.6*vap+13.3*radio
Commonly used optional per-AP CAPWAP bandwidth costs
Content Time (seconds) Payload (byte) Package bandwidth cost (bps)
AP scan 30 25+63*scanned-ap (66+25+63*scanned-ap)*8/30=24.26+16.8*scanned-ap
Total: 932.96+343.2*sta+9.6*vap+13.3*radio+16.8*scanned-ap
note icon Enabling WIDS features, LLDP, MESH, FortiPresence, and Client Station Locating Service can lead to additional bandwidth consumption.

There are 100 FortiAPs, with 187 stations distributed among them. Each FortiAP holds five VAPs among their radios, and each enables two radios. The basic CAPWAP bandwidth cost would be:

908.7*100+343.2*187+9.6*5*100+13.3*2*100 = 162.51kbps

Additionally, if two FortiAPs enabled "AP scan", and suppose one scans 99 APs in each scan and the other scans 20 APs in each scan, the additional CAPWAP bandwidth cost would be:

(24.26+16.8*99)+(24.26+16.8*20) = 2 kbps