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What is the purpose of area ID in FC ID?

  • 1.  What is the purpose of area ID in FC ID?

    Posted 03-05-2020 08:56 AM
    I have propably a very basic question, however i didn't find the answer. I can understand what is the purpose of Domain ID and Port ID in FC. But what is the purpose of  Area ID?
    Common explanations says it is used to identify group of port on FC switch. But that is the practical reason to diffirentiate one group of ports from another inside one switch?


  • 2.  RE: What is the purpose of area ID in FC ID?

    Posted 03-06-2020 04:28 AM
    @Andrey Ivanov  Andrey,  This might get a bit complex nowadays, although it started pretty simple in the old days of Fibre Channel.  Let's start simple...

    The 24bit address consists of  [DomainID] [Area ID] [AL_PA]   (Some might refer to AL_PA  as Port ID or Node ID).   From this address, you can determine which switch the device resides on from the domain ID, which port the device is attached to from the area ID, and if this device is part of a loop from the AL_PA number.    So the Area ID refers to the Port#, the AL_PA or Port ID  is only used for addressing a loop or NPIV device attached to that port. (These could be be the group of ports - I'd say (virtual) devices behind a physical port) you were mentioning)

    This way of generating the FC addresses is used for example in FICON environments or if you configure the "256-area addressing mode", but it only allows max of 256 ports in a switch/director.   For FC directors with more than 256 ports addressing gets a bit more complex and one can either use Virtual Fabrics / Logical Switches or switch to the 10bit addressing mode, that basically borrows one bit from the AL_PA to be able to address more physical ports. And then there's Zero-based addressing and Port-based addressing, but I don't want to go there...

    Senior Systems Engineer
    Broadcom - Brocade Storage Networking