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Help on adding a 3rd Cisco Switch

Posted on 2013-05-23
Medium Priority
Last Modified: 2013-05-23
I'm certainly not a savy Cisco network guy.  My objective is to add a third Cisco switch to my current setup.  I would appreciate it if I can get some directions on how to connect and configure the new switch and make all three working dandy. :). If connected correctly, the third switch can join the stack with minimal configurations, correct?  After it's joined, does the new switch inherits all the VLAN stuff too?

SWC1: C3560G
SWC2: C2960S
SWC3: C2960S

Currently SWC1 and SWC2 connection:
SWC1 port 5 <---> SWC2 port 1

Please shed some light on what's the best approach I should take.  Thank you in advance.
Question by:gbksphere
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Expert Comment

ID: 39191541
First, define your understanding of a "stack"

In the Cisco world, a stack is a group of switches connected by a specialized stack cable on the backside of the switches. From there the switches act as if they were one large switch with a single configuration, spanning-tree instance, etc.

Other manufacturers define a stack as a group of switches that have a single point of configuration even if they are all operating independently and physically separated.

A less technical definition of a stack is just the logical idea of 2 or more switches connected together, usually physically stacked on top of one another.

Once we know how you are planning to connect the new switch, we can tell you how it's done.

I do apologize if it sounds like I'm trying to point out a possible lack of networking knowledge, but the configuration and considerations vary greatly depending on how it's really being connected, and we don't like pointing people in the wrong direction if we can avoid it.

Author Comment

ID: 39191623
Thanks for reply.  You are correct though, I'm very limited on networking knowledge.  LOL.  In this case, there's no specialized stack or via stack cables at all.  Sry for using the term incorrectly.  I only have 2 switches connected to each other and I'm trying to add 1 more switch for more devices.
LVL 20

Accepted Solution

rauenpc earned 2000 total points
ID: 39191989
In that case, the best method to get things working and keep configs consistent is to use our wonder friend copy/paste. I assume the 3560 is the "core" switch or the switch acting as a gateway for devices. That being the [assumed] case, I would recommend you connect the new 2960 to the 3560, and prefer not to daisy chain switches from 3560-2960-2960. On the 3560, get the configuration of the port connected to the current 2960, and copy it to the port you will be connecting the new 2960 (update the description as necessary). Let's say the existing 2960 is in port 1, new 2960 will be port 2.

3560#show run int gig0/1
interface gigabitethernet0/1
description 2960s-1
sw trunk encapsulation dot1q
sw mode trunk

3560#config t
3560(config)#default int gig0/2
!the above clears all configuration on int gig0/2 so that previous commands don't mess with the commands you want to enter
3560(config)#int gig0/2
3560(config-if)#description 2960s-2
3560(config-if)#sw trunk encapsulation dot1q
3560(config-if)#sw mode trunk

As for the 2960 configuration, you should be able to copy/paste the entire configuration from the existing 2960. change the hostname and IP address as well as anything else you see that would need to be unique. Plug it in, and you should be good to go.

For a simple setup the above should be fine. there are situations where my recommendations will cause problems, but without me knowing all the details on your network I wouldn't know to avoid them. It may be a good idea to do this work outside of business hours in case an outage occurs.

Author Closing Comment

ID: 39192683
Awesome. Thanks for the assistance.

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