HP StorageWorks Fabric OS 6.2 administrator guide (5697-0016, May 2009)

178 Managing virtual fabrics
Figure 15 Logical Switches connected to form Logical Fabrics
The ISLs between the Logical Switches are dedicated ISLs because they carry traffic only for a single
Logical Fabric. In Figure 14, Fabric 128 has two switches (the default Logical Switches), but they cannot
communicate with each other because they have no ISLs between them and they cannot use the ISLs
between the other Logical Switches.
NOTE: If you connect two Logical Switches with different FIDs, the link between the switches segments.
Logical Fabric and ISL sharing
Another way to connect Logical Switches is using extended ISLs and base switches.
When you divide a chassis into Logical Switches, you can designate one of the switches to be a base
switch. A base switch is a special Logical Switch that is used for interconnecting the physical chassis. A
base switch has the following properties:
• ISLs connected through the base switch can be used for communication among the other Logical
Switches.
• For FC-FC routing, legacy EX_Ports must be connected to the base switch and no other Logical Switch.
• Base switches do not support direct device connectivity. A base switch can have only E_Ports, VE_Ports,
EX_Ports, or VEX_Ports, but no F_Ports.
• The base switch provides a common address space for communication between different Logical
Fabrics.
• A base switch can be configured for the preferred domain ID just like a non-Virtual Fabrics switch.
• You can have only one base switch in a physical chassis.
A base switch can be connected to other base switches through a special ISL, called a shared ISL or
extended ISL (XISL). The XISL is used to share traffic among different Logical Fabrics.
Fabric formation is not based on connectivity, but on the FIDs of the Logical Switches.
Figure 16 shows two physical chassis divided into Logical Switches. Each chassis has one base switch. An
ISL connects the two base switches. This ISL is an extended ISL (XISL) because it connects base switches.
Fabric 128
Fabric 1
Fabric 15
Fabric 8
SW1
SW8
SW4
SW7
SW3
SW6
SW2
SW5