To add a shared system to either the source or target side of a mirror, you must be connected to that system. You can connect to the system prior to starting the Manage Shared Volumes dialog, or you can click Connect to Server from within the dialog. In either case, if there are shared volumes that exist on that system that match either the source or target volume, the system and its matching IP address will be displayed in the correct page of the dialog. Leave the Include box checked to include the system in the job configuration and choose the correct IP address to be used for that system.
If a shared system does not have an IP address whose subnet matches the existing mirrored systems, the IP Address field will be blank and the Include box will be unchecked. You must reconfigure the system so that it has an IP address on that subnet. Then try adding the shared volume again.
When you click Done after adding a new shared system, it will be added to the job. If there are multiple mirrors in place, you will be asked to provide the network addresses to be used between the newly-added system and all other targets.