1-2 
 
z  For the details of the interface modules, refer to H3C S5120-EI Series Ethernet Switches 
Installation Manual. 
z  Among S5120-EI series switches, S5120-28C-EI, S5120-52C-EI, S5120-28C-PWR-EI, and 
S5120-52C-PWR-EI switches support IRF stack. 
 
You can connect physical stack ports of the S5120-EI series with either the CX4 dedicated cables or 
fibers according to the interface type on the interface module. Dedicated cables provide higher 
reliability and performance; whereas fibers connect physical devices located very far from each other 
and provide flexible application. 
The physical stack ports are numbered according to their physical locations on the rear panel of the 
S5120-EI series. With the rear panel facing you, the physical stack ports are numbered successively 
from left to right: ports on the interface module in slot 1 are numbered 1 and 2, and ports on the interface 
module in slot 2 are numbered 3 and 4, as shown in 
Figure 1-1, which illustrates an example of inserting 
a CX4 dual-port interface module. 
Figure 1-1 Numbering physical stack ports 
 
 
 
 
If you insert a one-port interface module into the slot, then the number of the physical stack port 
corresponding to the module in slot 1 is 1, and the number of the physical stack port corresponding to 
the module in slot 2 is 3. For the number of physical stack ports, see 
Configuring Stack Ports. 
 
Physical stack ports can be used for both stack connection and service data transmission. When 
establishing a stack, you need to specify that the physical stack ports are used for the stack, that is, bind 
them with logical stack port(s) to implement stack connection and establishment. 
Logical stack port 
You can set a physical stack port as a logical stack port, which is used to transfer data and protocol 
packets among stack members. An S5120-EI series can be configured with two logical stack ports, 
which are numbered 1 and 2, to connect other devices in a stack. 
An IRF stack typically has a bus connection or a ring connection: 
z  Bus connection: Given a device, its logical stack port 1 is connected to logical stack port 2 of 
another device, and its logical stack port 2 is connected to logical stack port 1 of a third one; 
devices are connected to form a single straight connection, as shown in 
Figure 1-2.