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cisco switch stacking

Posted on 2016-11-11
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Last Modified: 2016-11-14
How does redundancy/failover work in stacked switches? If I have a router with an uplink to master that has 4 more switches, if that master fails , how do the other 4  switches know how to get to the router since I dont have a link going to the router directly  from all the switches but only master? Or, do I need ethernet links from all switches to the router?
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Question by:Shark Attack
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by:Predrag Jovic
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You need at least two uplinks from 2 different switches in a stack to neighboring (upstream/downstream) device(s). Available uplink connection will be used (in the case that device with previously active uplink is not available). Also, it is recommended to use LACP for interconnection to the same neighboring device (if multiple links to the that devices are available).

Cisco Catalyst 3850 Series Switches StackWise-480 Architecture White Paper

According to configuration upstream devices are configured as VSS or vPC.
In the case that you have 2 uplinks to one device configuration is basically the same, except that less ports should be configured.
With 2 uplinks to two devices there would be no LACP configuration.
With 4 uplinks to 2 switches that are not configured as VSS or vPC there should be 2 channel groups (one channel-group to each upstream device).
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by:Shark Attack
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would the attached set up be OK? ESW1-5 is 1 stack and then ESW6-8 is second stack. Both stacks are on different floors. There are ether-channel links uplinks.

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Predrag Jovic earned 500 total points
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You can do it that way, but you can also do it this way.
stackLet's say that on stack on the left all interfaces connected to core are 1/0/49, 2/0/49, 4/0/49, 5/0/49
interface po1
 switchport mode trunk
!
interface range Gi1/0/49, Gi2/0/49, Gi4/0/49, Gi5/0/49
 switchport mode trunk
 channel-group 1 mode passive

Open in new window

Core configuration for left stack
interface po1
 switchport mode trunk
!
interface range Gi1/0/1 - 4
 switchport mode trunk
 channel-group 1 mode active

Open in new window


The same goes for stack on the right side (except that you have one port 50 there) :)
interface po2
 switchport mode trunk
!
interface range Gi1/0/49, Gi2/0/49, Gi3/0/49 - 50
 switchport mode trunk
 channel-group 2 mode passive

Open in new window

Core
interface po2
 switchport mode trunk
!
interface range Gi1/0/20 - 23
 switchport mode trunk
 channel-group 2 mode active

Open in new window

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by:Predrag Jovic
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This way the only difference is the number of uplinks that will be available if some device(s) quit. :)
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by:Shark Attack
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Thanks!
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by:Predrag Jovic
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You are welcome.
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