HP ProLiant BL25p Server-Blade - Manual (Page 15)

Component Identification 15
Server Blade Enclosure Bay Numbering
Each server blade enclosure requires a pair of interconnect modules to provide
network access for data transfer. Resolve bay numbering before determining
connections between the server blades and interconnects.
IMPORTANT: Note that server blade bay numbering in the figure is
reversed when looking at the rear of the enclosure.