Fibre Channel (FC) Addressing

Back to: FC (Fibre Channel) fundamentals

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.

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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.

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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.

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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.

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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.

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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).

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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.

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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.