please download and install IPAM 3.1 hot fix. This hotfix ensures the functionality concerning DHCP Option 003 - Router (you can see that on DHCP wizard page).
Hot fix is available on your customer portal or via direct link: http://downloads.solarwinds.com/solarwinds/Release/HotFix/IPAM-v3.1.0-HotFix1.zip
This HF is applicable only on IPAM 3.1
Please follow the installation steps below carefully.
1) Stop All solarwinds services ("Orion service Manager")
2) Copy and replace the Files to the installation directory "C:\Program Files (x86)\" OR "C:\Program Files\"
3) Run Configuration Wizard to completion, and select only Website option