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We have Cisco catalyst C3850-48T L3 switch in stack. and it is showing Active/Standby.

Question: what does standby mean in stack? Does it means if i plug my laptop on standby switch port it won't work? Can anyone explain what is the advantage of having switch in stack?

#show switch
Switch/Stack Mac Address : 6c99.8962.3990 - Local Mac Address
Mac persistency wait time: Indefinite
                                             H/W   Current
Switch#   Role    Mac Address     Priority Version  State
------------------------------------------------------------
*1       Active   6c99.8962.3990     15     M0      Ready
 2       Standby  1c1d.86a9.3500     1      M0      Ready
0
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The Active switch is the one which is the current master of the stack. Priority 15 is the highest priority, and the highest priority will be the master. If the master fails, the next highest priority will be the master.

A stack of switches acts like a single switch, and one switch is the master for the stack, but all the switches have the configuration, so if one switch fails, the stack lives on.

All the switches are actually working. The switches appear as if they were boards in a single chassis. The ports are referred to as <switch>/<slot>/<port>, like GigabitEthernet1/0/1.

The advantage of a stack is that you can lose a switch in the stack, and the stack still works. It's just like losing a board in a chassis - you lose those ports, but the chassis still works.

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  • For a stack of 3+ switches to work more like a chassis and survive the loss of any one switch, the top and bottom switches should connect directly to each other, creating a ring topology. – Paul Dec 1 '15 at 12:57
  • Yes, that is the preferred topology in Cisco's documentation on their stackable switches. – Ron Maupin Dec 1 '15 at 14:44
  • If i plug my computer on G1/0/1 (single wire) and that switch will fail in that case what will happen? – Satish Dec 1 '15 at 18:13
  • That switch fails, and none of the ports on that switch work, but the other switches in the stack will continue to work (e.g. G2/0/1). It's just like if you had a chassis switch and one of the boards in the chassis fails, the ports on that chassis will not work, but the rest of the boards and their ports will still be working. – Ron Maupin Dec 1 '15 at 18:19
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    No, it doesn't work like two independent switches. It works like a single chassis switch. You can do a port channel with ports on separate physical switches in a stack, but you can't do that with independent switches. You can also have the uplinks on separate switches. The failure of one physical switch doesn't bring down the stack, like the failure of a single board in a chassis doesn't bring down the chassis. – Ron Maupin Dec 1 '15 at 18:56

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