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Fibre Channel (SAN)

Posts: 0

Changing pricipal switch in a fabric

Hi All,


We have 2 x 24000 (FOS 5.3.2c) that, in a couple of weeks, we'll have to remove from our dual-fabric SAN. Unfortunately they are the principal switches for their respective fabric. Considering that I won't have any host/device device connection for that 24000s will it be any disruption for the data trafic for the rest of the fabric when I'll remove them from the fabric and a new pricipal switch would have to be elected?

Fro the rest of the fabric we have 6.2.0g, 6.2.2f, 6.4.1a and 6.4.3d FOS. In fact these 2 principal switches are the reason why we didn't yet move to 7.* FOS in the fabric.





Regular Contributor
Posts: 165
Registered: ‎05-11-2011

Re: Changing pricipal switch in a fabric

Hi Mugur,


when you remove the principal switch, you wil have a build fabric. That means that there is an new selection of an principal switch.

All Frames are forwarded by the ASICs, but during this time no host/device can log in. If you want to have a specific switch to become principal you can perform the fabricprincipal command on this switch. If you are not using option -f, the build fabric is done when you remove the 24000 or when there is another build fabric in between. If you use the -f option it is done immediatly.


Keep in mind that the new pricipal switch is responsible for the timesync in your fabric. If you are using an external ntp server be sure that the new principal can reach this server.



Kind Regards
Posts: 0

Re: Changing pricipal switch in a fabric

So, are you saying that by forcing a fabric rebuild a new principal switch (where I previously ran fabricprincipal) could be selected even if I would not remove the present principal but another switch?




Frequent Contributor
Posts: 80
Registered: ‎01-28-2010

Re: Changing pricipal switch in a fabric

yes it is possible, plus you can also define with a command which switches in the fabric you dont want to become the principal switch. but leave at least some switches in the fabric taht still can obtain this role, always think about a possible principal switch outtage


but before you do anything i would suggest you read the fos 720 admin guide for futher information


short summery

Principal switch
In a fabric with multiple switches, and one inter-switch link (ISL) exists between any two switches, a
principal switch is automatically elected. The principal switch provides the following capabilities:
• Maintains time for the entire fabric. Subordinate switches synchronize their time with the
principal switch. Changes to the clock server value on the principal switch are propagated to all
switches in the fabric.
• Manages domain ID assignment within the fabric. If a switch requests a domain ID that has
been used before, the principal switch grants the same domain ID unless it is in use by another


read about principal ISL so you understand what happens

Posts: 0

Re: Changing pricipal switch in a fabric

I have a customer who has introduced a DCX into the San Fabric and successfully merged. The Fabric consists of legacy switches Brocade 4100’s / B32’s OS v6.3.2b and a DCX running OS v7.1.0c .

I instructed the customer to move their principle switch selection to their DCX prior to decommissioning some of these legacy switches. However they are having troubles. Possibly my instructions are incorrect.


When they try to follow this they get

"The attempt was unsuccessful and failed with 'PSS principal failed (Lost to WWN 10:00:00:##:##:##:##:##) - FABR-1018."


The error suggests that it failed because there is already a principal switch with a lower WWN on the fabric.


Q: Should we have disabled all switches as participants for fabric principles including the current principle so that the DCX will become a principle ?

Valued Contributor
Posts: 761
Registered: ‎06-11-2010

Re: Changing pricipal switch in a fabric



Decrease the priority in the rest of the switchs, raise the priority on the DCX and repeat the operative to see if it works.



Occasional Contributor
Posts: 6
Registered: ‎03-18-2015

Re: Changing pricipal switch in a fabric

What is the command to decrease/increase priority?

Occasional Contributor
Posts: 16
Registered: ‎06-01-2016

Re: Changing pricipal switch in a fabric


I´ve used this way several times:


Command: Fabricprincipal
Set this command on present Principal switch:
>fabricprincipal --enable -p 0xff –f                         It will now get the lowest priority.


Set this command on the switch that shall become Principal switch:
>fabricprincipal -f 1





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