802.11r Fast Transition how to understand that FT works?

cotequeiroz · February 14, 2023, 10:29am

It works with 22.03 and master. See

openwrt/openwrt/blob/master/package/network/services/hostapd/files/hostapd.sh#L896-L944


      
          		if [ "$ieee80211r" -gt "0" ]; then
          			json_get_vars mobility_domain ft_psk_generate_local ft_over_ds reassociation_deadline
          
          
			set_default mobility_domain "$(echo "$ssid" | md5sum | head -c 4)"
          			set_default ft_over_ds 0
          			set_default reassociation_deadline 1000
          
          
			case "$auth_type" in
          				psk|sae|psk-sae)
          					set_default ft_psk_generate_local 1
          				;;
          				*)
          					set_default ft_psk_generate_local 0
          				;;
          			esac
          
          
			[ -n "$network_ifname" ] && append bss_conf "ft_iface=$network_ifname" "$N"
          			append bss_conf "mobility_domain=$mobility_domain" "$N"
          			append bss_conf "ft_psk_generate_local=$ft_psk_generate_local" "$N"
          			append bss_conf "ft_over_ds=$ft_over_ds" "$N"

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It will generate a default value for mobility_domain from the md5 of the ssid, and the key from the combination mobility_domain and PSK (or the EAP auth secret, if set). So this will work across routers, and it is good enough.

The caveat is that OpenWrt 21.02 will silently work with this setup, but it does not use the PSK to generate the FT key. So the key would be trivially calculated from the SSID alone That's why I do not usually advertise this setup.