Fibre Channel (FC) Addressing

Fibre Channel (FC) Addressing is a key concept in Storage Area Networks (SANs) that ensures proper communication between devices. FC networks use a hierarchical addressing scheme similar to IP addressing but optimized for high-speed, low-latency storage communication.

1. FC Addressing Structure

An FC address is a 24-bit identifier assigned to each device in a Fibre Channel fabric. The address is typically represented in hexadecimal format (e.g., 0x011700).

It follows this format:

| Domain ID (8 bits) | Area ID (8 bits) | Port ID (8 bits) |

Breakdown of the 24-bit FC Address:

  1. Domain ID (Bits 23–16)
    • Identifies a switch or a group of switches in a fabric.
    • Range: 0x01 to 0xEF (1-239).
  2. Area ID (Bits 15–8)
    • Represents a group of ports within a switch.
    • Used for logical segmentation.
  3. Port ID (Bits 7–0)
    • Identifies the specific port in the area.
    • This can be a host, storage, or another switch port.

2. FC Addressing Types

There are different types of FC addresses based on the role in the network:

  1. Well-Known Addresses (0xFFFFxx)
    • Reserved for fabric services like the Name Server (0xFFFFFC) or Fabric Controller (0xFFFFFD).
  2. Fabric-Assigned Addresses
    • Assigned dynamically to devices (N_Ports) when they join the fabric.
  3. Loop Addresses (0x00xxxx)
    • Used in Arbitrated Loop (FC-AL) environments.

3. WWN (World Wide Name) vs. FC Address

  • WWN (World Wide Name):
    • A globally unique 64-bit identifier for each FC device.
    • Assigned by the manufacturer (like a MAC address in Ethernet).
    • Example: 10:00:00:90:FA:12:34:56.
  • FC Address:
    • A 24-bit logical address assigned dynamically by the fabric.
    • It changes if the device moves to another switch, unlike WWN.

4. Address Discovery Process (Fabric Login)

  • When a device (N_Port) connects to a Fibre Channel switch (F_Port), it undergoes the FLOGI (Fabric Login) process:

    1. Device sends a request to the switch.
    2. Switch assigns a 24-bit FC address and registers the WWN.
    3. Device queries the Fabric Name Server for available targets (storage, etc.).
    4. Communication starts using FC address translation.

5. FC Addressing in Zoning

  • Zoning is used to control access between devices in the SAN.
  • It can be based on:
    • WWN Zoning (Preferred, since WWN is static).
    • FC Address Zoning (Not recommended, since FC addresses can change).

6. Example of an FC Address

Let’s say a host has been assigned an FC address of 0x021700:

  • Domain ID = 0x02 (Switch 2 in fabric)
  • Area ID = 0x17 (Logical area in the switch)
  • Port ID = 0x00 (Specific port in the area)

This address helps the switch route traffic efficiently in the SAN.

7. Key Takeaways

  • FC Addressing is hierarchical (Domain ID → Area ID → Port ID)
  • WWN is permanent, while FC addresses can change upon reconnection.
  • Fabric Login (FLOGI) assigns the FC address dynamically.
  • Well-Known Addresses (0xFFFFxx) handle fabric services.
  • Zoning can be done using WWN or FC Address, but WWN is preferred.
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