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Stacking switches reliably

Posted on 2011-09-07
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Last Modified: 2012-06-27
I have 2 server rooms in the office.  I will have 4 switches in each server room.  I want to connect them the best way possible.  How should I do it?

Currently in Room1 all of the switches have 2 ethernet cables connected to the switch1 and then the same in Room2.  Room2 also has 2 ethernet cables connected to Room1 switch1.  For some reason this is causing a problem when the 4th switch in Room1 was connected.  It brings down the network.

For example:

Room1  
switch1
switch2
switch3
switch4

Room2
switch1
switch2
switch3
switch4
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Question by:LrdKanien
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17 Comments
 
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Expert Comment

by:LHFoods
ID: 36499961
What brand/model of switches are you using?  Decent Cisco switches can be connected with a fabric interconnect.  Linksys and many other switches can be connected with LAG and LACP.
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Author Comment

by:LrdKanien
ID: 36500032
Netgear GS748TP
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Expert Comment

by:aleghart
ID: 36500059
Another thing to consider is that you may have a loop when you connect that last switch (Rm1-Sw4).  Make sure you don't have patch cables taking a direct or indirect route back to any other switches.  If you have STP (spanning tree protocol) enabled, the switches would detect the multiple pathways and choose only one.  Otherwise, you could have two or more ports answering for one device.  Mass confusion ensues.

I'm curious, how are you using 2 patch cables to link each switch?  Normally, you'd use a form of link aggregation (LAG, LACP, etc.) as LHFoods mentioned.

Have you tried linking up the equipment with a single patch first? If that works, then it points to a problem with your LAG creation.

network-uplink.jpg
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Expert Comment

by:LHFoods
ID: 36500069
Your best bet will be to install fiber SFPs and LAG those ports.  Linksys SFPs are reasonably priced and fiber patch cables can be picked up fairly cheap too.  If you don't want to spend the dollars for the SFPs you can always just use the copper ports in a LAG.  This document will give you a good start if you look under the LAG configuration:

ftp://downloads.netgear.com/files/GS700TP_SwAdmin_17Dec07.pdf
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Author Comment

by:LrdKanien
ID: 36500078
Please assume that I do nit want to purchase any special equipment to connect the switches.
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Expert Comment

by:aleghart
ID: 36500098
I have a couple of FSM7352PS switches...like yours, they don't have native stacking cables.  Mine do stack however.  Yours will only make uplinks.  But they will do LAG.

I'd troubleshoot by:
Making the single-cable connections first.
Ensuring all the switches are running the same firmware (doesn't have to be the most recent) and have the same/similar config (or re-flashed to factory settings).
Creating LAG between Rm1-Sw1 and Rm2-Sw1 first.  That will have the most traffic (in theory).

If connecting Rm1-Sw4 takes everything down, it sounds like STP is not running and you have a misconfigured LAG.

Are these running phones only, or combination of phones + computers?  If phones only, then LAG ports aren't necessary for speed.  They should be used for connection redundancy...and probably connected to each other instead of all back to the same Sw1.  48 ports at 90kb per port is 4.2Mbps...Fast Ethernet is enough.
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by:aleghart
ID: 36500114
>Please assume that I do nit want to purchase any special equipment to connect the switches.

You already have the SFP ports built into the switches.  They will accept fiber with the proper SFP "adapter".  The Linksys ones are 1/3rd the price of others.  I would use fiber for long runs...but my switches are all racked up in the same location.

Copper is fine for shorter runs that are clear of interference.
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Author Comment

by:LrdKanien
ID: 36500135
The switches are all connected via Ethernet and I don't know anything about SFP.

I would prefer to not have to buy adapters.  Can't I connect the switches over Ethernet and configure the ports a certain way for optimum performance and availability that way?
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by:aleghart
ID: 36500181
>Can't I connect the switches over Ethernet

Yes.  SFP is an alternative for when copper cables won't work.  Distance, interference, or running between buildings.

>and configure the ports a certain way for optimum performance and availability that way?

Yes.  Connect with single cables first.  When everything is working, then start to build the LAG ports.  You need to determine why you want multiple cables interconnecting the switches.  Is it speed, redundancy, or "just because"?

IMPORTANT: If you can't get them to work with single cables, it's useless to try connecting multiple cables and building LAG ports.  You have to fix the basic problems first.
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Author Comment

by:LrdKanien
ID: 36500185
Speed and redundancy.
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Expert Comment

by:aleghart
ID: 36500280
How much speed?  Phones?  Phones + desktops?  Phones + file & database servers?

If they are phones only, or phones + desktops, the 1000Base-T copper uplinks (single patch cable) will do just fine.  You'd need to design a ring pattern for redundant connections between the switches in each room.  STP will keep only work working at a time.

Keeping in mind that you have only 4 gigbit ports on each switch, and you may have only 2 physical cables between rooms, something like this would give you redundancy.  Using only gigabit ports.


network-uplink-redundant.jpg
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Expert Comment

by:aleghart
ID: 36500286
typo:  STP should keep only one path working at a time.
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Author Comment

by:LrdKanien
ID: 36500348
The switches are for phones and desktops.  I thought every port on the switch was gigabit.  Confirming with the docs.
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Expert Comment

by:aleghart
ID: 36500592
You're right.  All 10/100/1000 ports.  4 ports are combo gigabit/SFP.

For a faster trunk, build a 2-port LAG between rooms.  You lose some redundancy unless you have/install a third cable or more.
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Author Comment

by:LrdKanien
ID: 36500780
So create a LAG1 on each switch for the 2 ports that go between it and another switch?  Or?
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Author Comment

by:LrdKanien
ID: 36500874
What about utilizing the SFP for a trunk between the two rooms?  I don't have any fiber ran between the two rooms though.  Is there some kind of converter that works off those ports that can plug into my Ethernet jack on my punch down that connects to room 2?
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Accepted Solution

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aleghart earned 500 total points
ID: 36501207
SFP would take over for a gigabit port.  No advantage if you're using existing copper.

If you make a 2-port lag between each switch, you're usin up 6 ports on Sw2, Sw3, & Sw4.  Eight ports on Sw1.

Before going to this extreme, I'd connect all with single cables and make sure everything is working correctly.
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