Hi Manuel,
Thank you very much for your answer. Below are additional informations.
But I have a question: why the 4th member (the last member added to the stack) becomes Master despite the fact that it has the lowest priority ?
<A5120_PLC_3N_ASC>display version
HP Comware Platform Software
Comware Software, Version 5.20.99, Release 2220-US
Copyright (c) 2010-2013 Hewlett-Packard Development Company, L.P.
HP A5120-48G-PoE+ EI Switch with 2 Interface Slots uptime is 9 weeks, 3 days, 15 hours, 18 minutes
HP A5120-48G-PoE+ EI Switch with 2 Interface Slots with 1 Processor
128M bytes SDRAM
16384K bytes Flash Memory
Hardware Version is REV.B
CPLD Version is 007
Bootrom Version is 607
[SubSlot 0] 48GE+4SFP+POE Plus Hardware Version is REV.B
[SubSlot 1] 2 CX4 Hardware Version is REV.A
<A5120_PLC_3N_ASC>dis
<A5120_PLC_3N_ASC>display irf
Switch Role Priority CPU-Mac Description
1 Slave 32 3ce5-a6e2-ebb1 -----
2 Slave 31 3ce5-a6aa-fc38 -----
3 Slave 30 3822-d601-50fb -----
*+4 Master 29 d07e-2838-c054 -----
--------------------------------------------------
* indicates the device is the master.
+ indicates the device through which the user logs in.
The Bridge MAC of the IRF is: 3ce5-a6e2-ebad
Auto upgrade : yes
Mac persistent : 6 min
Domain ID : 0
<A5120_PLC_3N_ASC>
<A5120_PLC_3N_ASC>
<A5120_PLC_3N_ASC>display irf conf
<A5120_PLC_3N_ASC>display irf configuration
MemberID NewID IRF-Port1 IRF-Port2
1 1 Ten-GigabitEthernet1/1/1 Ten-GigabitEthernet1/1/2
2 2 Ten-GigabitEthernet2/1/1 Ten-GigabitEthernet2/1/2
3 3 Ten-GigabitEthernet3/1/1 Ten-GigabitEthernet3/1/2
4 4 Ten-GigabitEthernet4/1/1 Ten-GigabitEthernet4/1/2
<A5120_PLC_3N_ASC>
<A5120_PLC_3N_ASC>
<A5120_PLC_3N_ASC>display irf topo
Topology Info
-------------------------------------------------------------------------
IRF-Port1 IRF-Port2
Switch Link neighbor Link neighbor Belong To
4 UP 1 UP 3 d07e-2838-c054
1 UP 2 UP 4 d07e-2838-c054
2 UP 3 UP 1 d07e-2838-c054
3 UP 4 UP 2 d07e-2838-c054
<A5120_PLC_3N_ASC>
Regards
Ferdo