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LAG best practices for switching - Dell PowerConnect 6224

I want to connect two Dell Powerconnect 6224 switches with LAGs to increase bandwidth and make redundant connectivity.  

I'm using the GUI.  I can go to the LAG membership page and add the ports I want to LAG 1.  Let's say I want to use ports 23 and 24 on both switches.  I would set that on both switches.

The thing i'm worried about is causing some kind of loop once I connect them.  I've read a couple things that have me worried, such as "configure the LAG before you connect the switches."  Also some stuff about Spanning Tree Protocol.

So it sounds to me like there is some danger in what i'm doing and i'm not finding all the info I need to piece it together.  

Can a loop be caused by what I'm doing?  Does Spanning Tree need to be configured?  What are the logical steps to setting up LAGs without having issues?

thanks!
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readymade
Asked:
readymade
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4 Solutions
 
SepistCommented:
When you create a port channel such as a Dell LAG multiple ports get treated as one logical port, spanning-tree sees them as one logical port which removes the possibility of causing a spanning-tree loop on the LAG. The only way you would cause a loop is if you manually disabled spanning tree on the LAG.
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readymadeAuthor Commented:
I don't have spanning tree protocol enabled.  It's disabled on the switch by default.
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SepistCommented:
If you type `show spanning-tree` it comes up as disabled?
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readymadeAuthor Commented:
Once again i'm using the GUI.  

Spanning Tree Protocol is not enabled on the switch by default.  Are you saying when I create a LAG, that STP is enabled on those ports automatically?
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SepistCommented:
No, I was trying to figure out if it was spanning tree or spanning tree portfast that was disabled, as no managed switch would sanely disable STP by default and if it did I would throw it into the nearest trash can.
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readymadeAuthor Commented:
You are right.  Spanning Tree is enabled.  Portfast is not.  My apologies.  From what I had read, I thought for sure STP was something you needed to choose to turn on.  

So I should not worry about loops at all?  

What's with people saying you should configure the LAG before connecting the switches?
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SepistCommented:
Best practices would be to configure the LAG first so spanning tree doesn't undergo any kind of recalculations when the ports change from up / down / up again
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readymadeAuthor Commented:
I connected the switches and had no problems with the LAG.  The switches showed all four ports as active as LAGs.  For devices on the opposite switches to be able to reach each other, I did have to add that LAG as a VLan member.  Makes sense, but i'm new to this.

Thanks for the help Sepist.  I will award you the points.  Question though, do you know of a way for me to test the speed in a way that would allow me to unplug one of the LAG ports and see the difference between the two connections vs one?  I only have one computer plugged into each switch, and it's an issolated network.  I wasn't able to see a difference in large pings or copying files between the computers.  Thanks!
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SepistCommented:
This is really out of the realm of something I would do normally (I do more engineer work) so
I can't really get into the details but you could run iperf on both machines to test max throughput by passing udp packets across the LAG, the first test could be a benchmark and a second test you could pull a port out of the LAG and see what how different it looks than your benchmark.
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