Fibre Channel (SAN)

Posts: 45
Registered: ‎06-04-2012
Accepted Solution


Hi Friends,


Just wanted to understand, why we need to two actions PLOGI and PRLI for a device to talk to its zone partners?


During PLOGI, NS Query, the source device gets the list of all the targets it can talk to? 

And, NS probe followed by NS query will check the status of the target devices.


I dont feel the need of PRLI here. Please clarify


Thanks in Advance.

Occasional Contributor
Posts: 8
Registered: ‎02-08-2018


Hello DattaSal,

Here are the login steps from the Administrator Guide on why PRLI is needed:


Port login process

The steps in the port initialization process occur as the result of a protocol that functions to discover the type of device connected and establish the port type and negotiate port speed. See Port Types for a discussion of available port types.

The Fibre Channel protocol (FCP) auto discovery process enables private storage devices that accept the process login (PRLI) to communicate in a fabric.

If device probing is enabled, the embedded port performs a PLOGI and attempts a PRLI into the device to retrieve information to enter into the name server. This enables private devices that do not explicitly register with the Name Server (NS) to be entered in the NS and receive full fabric access.

A fabric-capable device registers its information with the name server during a FLOGI. These devices typically register information with the name server before querying for a device list. The embedded port still performs a PLOGI and attempts a PRLI with these devices.

If a port decides to end the current session, it initiates a logout. A logout concludes the session and terminates any work in progress associated with that session.

To display the contents of a switch’s name server, use the nsShow or nsAllShow command. For more information about these commands, refer to the Fabric OS Command Reference.



Peter O'Brien
Posts: 45
Registered: ‎06-04-2012


Thanks Peter for the reply. 


From your reply,


1) In what scenario do we see private devices(the ones which do not register itself into NS)?

2) The FCP auto discovery happens at which stage? After FLOGI or PLOGI or SCR?

3) You said a fabric device registers its information into NS during FLOGI. But that happens after PLOGI, exactly after SCR?

4) So, I understand in simple language that a PRLI is nothing a fabric communication established between initiator and target devices for scsi exchange? And a PLOGI is just like an authentication (can I talk to you?).


Kindly clarify.


Many Thanks!!!

Regular Contributor
Posts: 164
Registered: ‎02-05-2014


A PLOGI is seen on two occasions. First one is to have the N-port to register with the name-server in the fabric and the second one is between N-ports to exchange session parameters. (ie what do each of the partners support on a FC frame,transmission and services layer).


A PRLI is required to estblish an FC4 session (Can be FCP, Ficon, IPFC, NVMe and any other layer 4 process) in order for the two entities to be able to use the correct protocols and protocol options.


Hope this helps.

Kind regards,
Erwin van Londen
Brocade Distinguished Architect The Fibre Channel blog

Q&A ->

Posts: 45
Registered: ‎06-04-2012


Thanks a lot Erwin. Its much clear now. I have read some of your blogs on Brocade, very explanatory. Thanks again!!!

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