Send documentation comments to mdsfeedback-doc@cisco.com.
24-4
Cisco MDS 9000 Family Fabric Manager Configuration Guide
OL-6965-03, Cisco MDS SAN-OS Release 2.x
Chapter 24 Additional Configuration
Flat FC ID Allocation
•In Cisco MDS SAN-OS Release 2.0, both ELPs and EFPs use the VSAN WWN by default during
link initialization. However, the ELP usage changes based on the peer switch’s usage:
–
If the peer switch ELP uses the switch WWN, then the local switch also uses the switch WWN.
–
If the peer switch ELP uses the VSAN WWN, then the local switch also uses the VSAN WWN.
This link initialization change between Cisco MDS SAN-OS releases is implicit and does not require
any configuration.

Flat FC ID Allocation

Fibre Channel standards require a unique FC ID to be allocated to an N port attached to a Fx port in any
switch. To conserve the number of FC IDs used, Cisco MDS 9000 Family switches use a special
allocation scheme.
Based on the assigned FC ID, some HBAs assume that no other ports have the same area bits and domain.
When a target is assigned with an FC ID that has the same area bits, but different port bits, the HBA fails
to discover these targets. To isolate these HBAs in a separate area, switches in the Cisco MDS 9000
Family follow a different FC ID allocation scheme. By default, the FC ID allocation mode is auto mode.
In the auto mode, only HBAs without interop issues are assigned FCIDs with specific port bits. All other
HBAs are assigned FC IDs with a whole area (port bits set to 0). The three options to allocate FCID are
auto (default), none, and flat.
Caution Changes to FC IDs should be made by an administrator or individual who is completely familiar with
switch operations.

Loop Monitoring Initiation

By default, the loop monitoring is disabled in all switches in the Cisco MDS 9000 Family. When a disk
is removed from a loop port, the loop stays active based on the bypass circuit. Thus the disk removal is
not known until you try to communicate with the disk. To detect such removals, the disks can be polled
periodically (every 20 seconds).
Caution Changes to the loop monitoring feature should be made by an administrator or individual who is
completely familiar with switch operations.

Switch Interoperability

Interoperability enables the products of multiple vendors to come into contact with each other. Fibre
Channel standards guide vendors towards common external Fibre Channel interfaces.
If all vendors followed the standards in the same manner, then interconnecting different products would
become a trivial exercise. However, not all vendors follow the standards in the same way thus resulting
in interoperability modes. This section briefly explains the basic concepts of these modes.
Each vendor has a regular mode and an equivalent interoperability mode, which specifically turns off
advanced or proprietary features and provides the product with a more interoperable standards compliant
implementation.