Hostapd does not contact radius server

[Guan Xin]

Hello,

I have configured hostapd 2.5 (did not try other versions) to provide
WPA-EAP access.

However, when I run either another hostapd process as a radius server
on the AP, or run freeradius on another host that has a wired
connection to the AP,
the (radius client) hostapd does not contact the radius server.
I checked this with iptraf, and saw no packet from/to port 1812.
I tried to send something using netcat from the AP to port 1812 where the
freeradius server is listening, and actually got a response.
So I don't think this is a problem of some firewall.
Actually I didn't setup any firewall on port 181*, and the AP is connected
directly to the computer running freeradius with an ethernet cable.

Any hints are appreciated. Thanks in advance!

Guan

P.S. Configuration of hostapd:

ctrl_interface=/var/run/hostapd
ctrl_interface_group=0

interface=wlan1
bridge=br0
driver=nl80211
hw_mode=g
channel=13
ieee80211n=1
ht_capab=[SHORT-GI-20]
require_ht=1
beacon_int=97
wmm_enabled=1
dtim_period=1
ap_max_inactivity=30

ssid=MySSID
ignore_broadcast_ssid=0

auth_algs=1
ieee8021x=1
own_ip_addr=192.168.123.1
auth_server_addr=192.168.123.3 # or 127.0.0.1 when running on the same machine
auth_server_port=1812
auth_server_shared_secret=testing123

wpa=2
wpa_key_mgmt=WPA-EAP
wpa_pairwise=CCMP
rsn_pairwise=CCMP

# -- End of hostapd.conf -- #