Brocade Fabric OS Administrators Guide (Supporting Fabric OS v7.3.0) - Manual (Page 278)

FIGURE 28 Logical fabric using ISLs and XISLs
By default, the physical ISL path is favored over the logical path (over the XISL) because the physical
path has a lower cost. This behavior can be changed by configuring the cost of the dedicated physical
ISL to match the cost of the logical ISL.
ATTENTION
If you disable a base switch, all of the logical ISLs are broken and the logical switches cannot
communicate with each other unless they are connected by a physical ISL.
Base fabric
Base switch ports on different chassis can be connected together to form a fabric, called a base
fabric . Similar to other logical switches, the base switches must have the same FID to be connected.
If the base switches have different FIDs, the link between the switches is disabled.
The base fabric follows normal routing policies. As long as physical connectivity is available, the base
fabric maintains connectivity for the logical fabrics.
Logical ports
As shown in Figure 28 on page 278, logical ISLs are formed to connect logical switches. A logical port
represents the ports at each end of a logical ISL. A logical port is a software construct only and does
not correspond to any physical port.
Most port commands are not supported on logical ports. For example, you cannot change the state or
configuration of a logical port.
The World Wide Name (WWN) for logical ports is in NAA=5 format, using the following syntax:
5n:nn:nn:nz:zz:zz:zx:xx
Base fabric
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