Edit the /etc/dansguardian/dansguardian.conf file and set the filterip to your machines local IP:
# the IP that DansGuardian listens on. If left blank DansGuardian will
# listen on all IPs. That would include all NICs, loopback, modem, etc.
# Normally you would have your firewall protecting this, but if you want
# you can limit it to a certain IP. To bind to multiple interfaces,
# specify each IP on an individual filterip line.
filterip =
(e.g. filterip=192.168.1.1)