basst42 did you read page 423?
3Create the XRN Distributed Fabric as follows:
■Switch 5500 Family — via the two SFP ports (27/28 or 51/52 depending on type of Switch), however, before connecting up, enable the Fabric ports on the Switch units using the instructions in the “Creating an XRN Distributed Fabric” Chapter in the Getting Started Guide that accompanies your Switch.
if you look at page 147 the manual gives you an example of routing between two switches.