Port Indexes and Multigeneration Modules

This post is to highlight something that is already mentioned on cisco.com, but you may not be aware of.  That is the number of port indexes consumed by various MDS modules.

* A Port Channel can be considered a logical port but it does not consume a port index rather the interfaces that comprise the Port Channel consume them.
** Each port IP services physical interface supports up to three FCIP tunnels. Therefore every IP services physical interface is assigned four index IDs, there for FCIP and one for iSCSI.

You can also get access to this information from the CLI by using the show port index-allocation command:

Take careful note of the IPS-4, IPS-8 and 14/2 modules. These modules have Gigabit Ethernet ports onboard which can be used for either iSCSI or FCIP. FCIP has a limit of three tunnels per port. In addition to three tunnels of FCIP, each port can have iSCSI/iSLB configured. Each of these takes up a port index, so each gigabit port reserves 4 port indexes. As noted in the above chart, port-channels do not consume port-indexes separate from those already consumed by their members.

It’s also important to realize that port indexes are allocated in the order the modules power up. Modules power up based on the slots they are in, starting with the first slots. Generation 1 modules have to start on an even boundary of 32 (0, 32, 64, etc). This is not a restriction on Generation 2 modules. For this reason Generation 1 modules need to be installed before Generation 2 modules, otherwise there could be an issue in port index allocation and the module will not come up. To correct this you need to power off the generation 2 modules, power on the generation 1 modules, and then power on the generation 2 modules. This can be done using the poweroff module command.