HP Mainframe Connectivity Design Guide

The routing type is determined by the number of directors between the mainframe and the CU, not
the number of directors in the fabric.
• If the mainframe and CU are connected to the same director, single-director routing is used.
• If the mainframe and CU are connected to two different directors, and there is at least one
ISL or ICL between the directors, cascaded-director routing is used.
HP supports multiple ISLs between the two directors if the directors support guaranteed in-order
delivery of the FICON frames over multiple ISLs. This support varies depending on the FICON
director series and model.
NOTE: FICON supports a one-hop maximum between the mainframe and the CU. FICON does
not support interfabric routing. All mainframes and CUs must be in the same fabric, zone, Meta
SAN, or VSAN.
Defining FICON routes
All routing from the mainframe to the CU is configured in the mainframe.
FICON mainframes and operating systems support the following:
• Direct-attached storage (point-to-point without a SAN)
• 1-byte link addressing (CU connected to the same director as the CHPID)
• 2-byte link addressing (CU and CHPID connected to cascaded directors)
NOTE: HP supports all versions of z/OS and OS/390. Only zSeries mainframes running z/OS
V1R3 (with patches) or z/VM V4R4 or later, and all z9 or later mainframes support 2-byte link
addressing (cascaded directors).
FICON SAN routing is static routing defined in the mainframe configuration. The operating system,
HCD, and CU must support 2-byte destination link addressing in order to support cascaded FICON
directors.
The 2-byte destination link addressing was added to the zSeries (z/OS) systems starting with V1R3.
Prior to that release, mainframes could only support 1-byte destination link addressing. This single
byte identified the egress port on the director for the CU. There was no capability to address a
second director, so cascaded FICON directors were not supported. With 2-byte destination link
addressing, the first byte of the destination link address identifies the destination director, and the
second byte identifies the egress port on that director for the CU.
A CU connected through a cascaded FICON director must be defined using a 2-byte link address
in the HCD.
NOTE: When a 2-byte destination link address is defined on a CHPID, all CUs defined on that
CHPID must use 2-byte destination link addresses, even if the CU is attached to the same director
as the CHPID.
Figure 8 (page 25) shows a FICON SAN using 1-byte destination link addressing. There is one
CHPID (01) and one entry director (switch 01). The switch ID is not required for routing in a
single-switch fabric. The paths to the CUs are defined on CHPID 01 in the IOCP Link statement.
CU 1000 uses port 20, CU 2000 uses port 21, and CU 3000 uses port 22. CHPID 01 uses port
10.
24 FICON SAN fabric topologies