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LAN Design Question


Hi Team, i need some information regarding LAN Design, Please see Diagram 1 Current Setup. in which when our Core switch trunk ports are full we install 2 aggregate switches and connect both aggregate switches with core switches.

but mostly in documentation i see connectivity as mentioned in 2nd diagram with name "setup online" , where RED lines are added, i mostly see such full mesh physical connectivity.

May i know if there is any real problem in first design? where we only connect Core1 with Aggregate 1 and Core 2 with aggregate 2?

thank you in advance.

Just to add HSRP is running on LAN side between both Core and all LAN gateway are on Core switches. and EIGRP is running between 2 routers and 2 Core switch.


6 Replies 6

Leo Laohoo
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You need to define what your "core switch" is.  What model?


If the core switch is a model which does not support stacking, then all I can say is that someone is planning to "burn" three ports (instead of two) for the sake of redundancy.  


This "setup_online" design is very, very old school.  I have never seen any setup like this.  

Hello LEO Core switch(Primary and Secondary Gateway) are 3560G Layer 3 switches at TOP connected with Routers.

and Aggregate are newer 2960X Layer 2 in middle written as aggregate.

Leo Laohoo
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Wow ... 3560G core and you want to do multiple redundant links.  One word will sum this all up:  NIGHTMARE.  


On paper, you'll be able to get this right by fine-tuning STP, PVSTP, MSTP, etc.  In the real world, I wouldn't touch this scenario.  Not with a switch that does NOT support stacking.  

Let's say your core is a stack of 3750G/E/X or 3650 or 3850 and your access switch are 2960S/X/XR.  If this is the case, then you'll have a pair of routers with their links going down to a stack of 3750 and from the stack of 3750 you have links going down to the access switch.  


NOTE:  I'm holding back the "method" because I'm waiting for more information from you.

Sorry for getting back late on this :) so many things going on.

so you think my setup_current design is nightmare or setup_online i am trying to achieve is nightmare :) i am running Setup_current design in 2 offices without problem so far, and if Layer 3 Primary Gateway 3560G goes down or Cable connection to Layer 2 aggregate go down, then traffic from Tail switch still go via this path, Come to Layer 2 aggregate 1(left side) then take fiber connection to Layer 2 aggregate 2 and -> Layer 3 2ndry GW--> via L2 trunk Layer 3 Primary GW and out :)

Please suggest, if i should stick with it? or adding more connection like setup_online diagram is showing, has any real benefits?

Leo Laohoo
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What you currently have may work but you need to get on with the times.  


This is why the trend nowadays are switches that can be stacked to form a logical unit.  Switches like the 2960S/X/XR, 3650 and 3850 all support switch stacking.  The new supervisor cards for the 4500, Sup7 & Sup8, now support VSS.  The supervisor cards for the 6500/6800X support VSS.  


If you have the opportunity to set up a new LAN from scratch, switch stacking and/or VSS should be the cornerstone of your LAN.  

Agree with you. Waiting for these switches to get burnt so that we can buy new one. lolz.

Thank you for your time and assistance.

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