Fibre Channel Basics

The purpose of this post is to keep track of my notes as I learn Fibre Channel. The plan is to read as much as I can and then try to work on configurations. I'm working on building a small lab to learn the basics.

Speeds supported are 1,2,4,8 and 16 Gbps

Topologies
 
Point-to-point (FC-P2P) - Two and only two directly connected devices
Arbitrated Loop (FC-AL) - Similar to Token Ring. Only a pair of ports can communicate at the same time.
Switched Fabric (FC-SW) - Multiple pair of ports can communicate at the same time.

Tables taken from the Wikipedia:
Attribute Point-to-Point Arbitrated loop Switched fabric
Max ports 2 127 ~16777216 (224)
Address size N/A 8-bit ALPA 24-bit port ID
Side effect of port failure Link fails Loop fails (until port bypassed) N/A
Mixing different link rates No No Yes
Frame delivery In order In order Not guaranteed
Access to medium Dedicated Arbitrated Dedicated

FC Basic Port Types
  • N_port is a port on the node (e.g. host or storage device) used with both FC-P2P or FC-SW topologies. Also known as node port.
  • NL_port is a port on the node used with an FC-AL topology. Also known as Node Loop port.
  • F_port is a port on the switch that connects to a node point-to-point (i.e. connects to an N_port). Also known as fabric port. An F_port is not loop capable.
  • FL_port is a port on the switch that connects to a FC-AL loop (i.e. to NL_ports). Also known as fabric loop port.
  • E_port is the connection between two fibre channel switches. Also known as an Expansion port. When E_ports between two switches form a link, that link is referred to as an inter-switch link (ISL).
FC Naming

Each HBA is assigned a WWN
Each port on the HBA is assigned a Port WWN or PWWN
These are 64 bits in length

FCID is a 24 bit value assigned by the fabric when a device logs into the fabric. The FCID serves a similar purpose to IP addressing in a LAN.  FCIDs are used to route frames across the fabric.

Domain ID - A domain ID is a unique identification number provided to each switch in the fabric. The Domain ID and the port number associated with an Nx_Port's connection to the fabric are unique parts of the 24 bit Fiber Channel address for the Nx_Port.

NPIV - N_Port Identifier Virtualization is when a Fibre Channel facility allows multiple N_Ports to share a single physical N_Port.  NPIV allows multiple initiators to occupy a single physical N_Port. NPIV provides a means to assign multiple FC IDs to a single N port, and allows multiple applications on the N port to use different identifiers. NPIV also allows access control, zoning, and port security to be implemented at the application level

NPV -  N_Port Virtualization aggregates multiple locally connected N ports into one or more external NP links, which shares the domain ID of the NPV core switch among multiple NPV switches. NPV also allows multiple devices to attach to the same port on the NPV core switch, thereby reducing the need for more ports on the core.

FC Services
  • Fabric F_Port/ Login Server - This service provides the Fabric Login (FLOGI). Well known address is FFFFFFFE.
  • Fabric Controller - Well known address is FFFFFFFD
  • Directory Server - Well known address is FFFFFFFC
  • Management Server - - Well known address is FFFFFFFA
Zoning

Zoning is a process that is used to partition a Fiber Channel fabric into subsets mostly for security.   There are two methods of zoning; soft and hard.  Soft zoning restricts only the fabric name service.  Hard zoning restricts actual communication across the fabric.

Zone Sets
Zone Sets are a grouping of zones to enforce access control in the fabric.


Either zone set A or zone set B can be activated (but not together). Taken from the Cisco SAN OS configuration guide.

Port and WWN Zoning
Zoning can be used to either the switch port a device is connected to or the WWN on the host being connected.

VSANs
Virtual SANs provide isolation among devices physically connected to the same fabric. Up to 239 Switches can be in a fabric and FC ID's do not need to be unique across the VSANs.


VSANs Versus Zones
You can define multiple zones in a VSAN. Because two VSANs are equivalent to two unconnected SANs, zone A on VSAN 1 is different and separate from zone A in VSAN 2.

VSAN Characteristic
Zone Characteristic
VSANs equal SANs with routing, naming, and zoning protocols
Routing, naming, and zoning protocols are not available
on a per-zone basis.
—
Zones are always contained within a VSAN. Zones never span two VSANs
VSANs limit unicast, multicast, and broadcast traffic.
Zones limit unicast traffic
Membership is typically defined using the VSAN ID to Fx ports
Membership is typically defined by the pWWN.
An HBA or a storage device can belong only to a single VSAN—the VSAN associated with the Fx port
An HBA or storage device can belong to multiple zones.
VSANs enforce membership at each E port, source port, and destination port.
Zones enforce membership only at the source and
destination ports.
VSANs are defined for larger environments (storage service providers).
Zones are defined for a set of initiators and targets not
visible outside the zone.
VSANs encompass the entire fabric.
Zones are configured at the fabric edge.
* this table was taken from the Cisco MDS 9000 Family CLI Configuration Guide

Dynamic VSANs
VSAN membership can be dynamically assigned by the device WWN instead of the physical port. This way, if a device is moved to a different port, the VSAN membership is retained.

Inter-VSAN Routing (IVR)
Initiators and targets are allowed to access each other on different VSANs.

IVR-NAT
IVR-NAT provides the ability to re-use virtual Domain IDs on each switch.

Fabric Login (FLOGI)
A FLOGI request is the first frame sent when a N-Port becomes active.  The N_Port uses the FLOGI frame to request access to the fabric and to get an FCID.  The FLOGI request contains both the N_Ports WWN and PWWN as well as the classes of service.

Device Alias
A device alias is a user friendly name for a port WWN.  Device alias are distributed across all switches in the fabric by default.

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