Hi @thetrung,
If you are using openHAB 2, your /etc/openhab2/services/knx.cfg should look like:
# KNX gateway IP address
ip=224.0.23.12
# KNX gateway port
port=3671
# KNX IP connection type
type=ROUTER
# Local KNX Binding bus address
busaddr=0.0.0
# Local endpoint
localIp=100.100.100.20
# Ignore local KNX Events
ignorelocalevents=true
The IP subnet that you are using (100.100.100.x) is a strange one (meaning that it is not a private one - see RFC 1918). That’s ok and it will work but I wouldn’t use it.
Good Luck!