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Fabric OS Administrator’s Guide 283
53-1002745-02
Logical fabric overview
10
Base switch and extended ISLs
Another way to connect logical switches is to use 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.
• 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). An extended ISL connects base switches. The XISL is used to share traffic
among different logical fabrics.
Fabric formation across an XISL is based on the FIDs of the logical switches.
Figure 25 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.
FIGURE 25 Base switches connected by an XISL
Traffic between the logical switches can now flow across this XISL. The traffic can flow only
between logical switches with the same fabric ID. For example, traffic can flow between logical
switch 2 in chassis 1 and logical switch 6 in chassis 2, because they both have FID 1. Traffic cannot
flow between logical switch 2 and logical switch 7, because they have different fabric IDs (and are
thus in different fabrics).
Base switch
Fabric ID 8
P9
Logical switch 7
Fabric ID 15
P7
Logical switch 6
Fabric ID 1
P4
Logical switch 5
(Default logical switch)
Fabric ID 128
Physical chassis 2
Base switch
Fabric ID 8
P6
Logical switch 3
Fabric ID 15
P5
Logical switch 2
Fabric ID 1
P2
Logical switch 1
(Default logical switch)
Fabric ID 128
P1
Physical chassis 1
P8
P6
P2
P1
XISL