I have a 3845 and going through the configuration, I see that there is an IDS module.
In the config, I see loopback interfaces but am unsure what they are used for....
ip address 192.168.0.3 255.255.255.0
ip address 184.108.40.206 255.255.255.0 secondary
ip address 220.127.116.11 255.255.255.0
ip address 18.104.22.168 255.255.255.0
ip address 22.214.171.124 255.255.255.0