D-Link DFE-2600 User Manual page 52

Dual-Speed Stackable Hubs User's Guide
The figure above shows an unsegmented hub stack. All hubs in the stack are
in the same collision domain because they are connected together through the
daisy-chain ports.
The figure below shows a stack divided into three separate collision domains.
Hubs three and four are isolated from the main segment (collision domain
one) using the hub's segmentation capability, putting them into their own
isolated collision domains two and three respectively. A switch, bridge or
router can be used to connect the three collision domains so that traffic can
pass between them, yet keeping them isolated to reduce congestion on each
segment.
40 Master Hub Setup and Management