Brocade FICON Administrator’s Guide (Supporting Fabric OS v7.3.0) - Manual (Page 46)

An extended interswitch link (XISL) is an interswitch link (ISL) that connects the logical switch to a
base switch and carries traffic for multiple logical fabrics. The XISL is a logical switch feature, not
a link feature. It is shared by multiple logical switches and can be used for multiple Fabric IDs
(FIDs). Creating an XISL is disruptive because it provides a core routing function for the switch.
For more information on creating XISLs and restrictions, refer to the configure command in the
Fabric OS Command Reference.
When using XISLs, the effective routing policy for all logical switches configured to allow XISL use
is that of the base switch regardless of how the routing policy is defined. The best practice is to
set the routing policy in all logical switches that allow XISL use to have the same routing policy as
the base switch to avoid confusion about the routing policy used. A base switch can only be used
for XISLs. Therefore, the switch cannot be managed through a CUP port and cannot report
statistics for RMF.
Port-based routing (PBR) and device-based routing (DBR) are qualified for System z; however,
reference your system qualification letter for current support information. The recommended
policy is DBR or aptPolicy 2.
• If addresses 0xFE or 0XFF have been assigned to physical ports, those ports must be disabled
before FMS can be enabled.
• Each logical switch has its own configuration data, such as the following:
‐ Initial Program Load (IPL) file.
‐ Configuration data elements, such as Prohibit Dynamic Connectivty Mask (PDCM),
Product Information Broker (PIB), port address names, mode register, and key counter.
‐ CUP configuration files.
• Ports moved into a logical switch will have persistent states based on the Active=Saved (ASM) bit
setting and other factors. Refer to
Disabling and enabling ports - persistent states on page 46
for more information.
Addressing modes
The following 256-area addressing modes provide extended functionality in dynamically created
partitions:
• Mode 0 - 10-bit addressing
• Mode 1 - zero-based addressing
• Mode 2 - port-based addressing
Mode 0 (10-bit addressing)
Mode 0 is called “Disabled” in the Brocade Network Advisor. It is not supported for FICON, but can be
used for mainframe FCP channels associated with zLinux or zVM partitions. That is, on a chassis in a
FICON environment, you can utilize a logical switch or default switch only in Mode 1 (zero-based
addressing) for FICON, even if Mode 0 is enabled on a different non-FICON logical switch.
Mode 0 uses the two upper bits in the ALPA to address up to 1024 ports in a single logical switch.
Because a 64-port blade is the highest port count blade available and eight slots is the highest slot
count available in a Brocade chassis, the practical address limit is 512 ports. Because NPIV also uses
ALPA bits, this address mode leaves just 6 bits for NPIV. Therefore, the maximum NPIV logins is
limited to 64 (63 practical), not 256.
Mode 0 is supported on chassis switch models only when one of the following is true (typically for
customers upgrading from FOS v6.x):
Addressing modes
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