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adding switches to the core

I currently have two 3560 L3 switches running HSRP and etherchannel between them. These core switches are configured with separate vlans for different traffic such as (iscsi,nfs,vmnet,network,server) and all nodes are plugged in to the core. Since these aren't stackable, one is used as the "active" switch and the other as the "standby"

We are running out of ports so I will be adding two 2948 to this setup and would like to know the best practice to accomplish this.

Current setup for esx hosts and storage devices.

"Active NIC1" --->CORE1==CORE2<---"Standby NIC2"

When I add the 2948s to each core which traffic should I move off the core to these two switches?

For instance, should I take ISCSI off the 3560 and put on the 2948s?


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      sw1    sw2

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adding switches to the core


Firstly I would suggest you to enable VTP and also use VTP prune concept.
Secondly you can connect the 2948 to two corse (mesh) and configure trunk on the uplink port and allowed Vlan's which are necessary.

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Re: adding switches to the core

Are these the 2948 switches -

If so be aware that they have a 20Gbps forwarding fabric so once you go above 20 connected ports then you are going to get oversubscription. Not necessarily a problem but something to be aware of.

If you only have these 3560s and the 2 2948s you can either run VTP transparent but it does mean you will need to manually create the vlans on the 2948s or you can go with Naidu's setup of VTP Server/Client and use VTP pruning.

Connect each 2948 to both 3560 switches with trunks and if you manually configure which vlans are allowed on the trunk then you don't need to worry about VTP pruning.

STP (spanning tree). Have you manually set the 3560s to be STP root and secondary ? If not it would be a good idea to do so. This will stop the 2948s becoming STP root/secondary.

Connect these switches up out of hours ie. you need an outage to do all this.



adding switches to the core

Yes these are 2948s and thanks for you letting me know the forwarding fabric.

I checked and my 3560 has 32GBs and the 2948 does have 20GBs.

Since it would only allow 20 connected ports of the 48 ports would it not be considered a non-blocking switch?

STP root is configured already on the 3560.


Re: adding switches to the core

Could I suggest that you dedicate the two new switches to iSCSI as this would give you a very simple topology. They would not need to connect to any other switch except for management. This would also give you the 'perfect' iSCSI setup as recommended by several vendors (i.e. two separate unconnected iSCSI ethernet domains).

As an alternative, if you want to trunk many VLANs to the new switches you could consider the 2960-S series switches at they have a stackable option. See



adding switches to the core

I think I may like this idea of a separate dedicated to iscsi which would make it much simpler.

Although we are new to iscsi, maybe i can just use the switches for the storage network being a vlan for nfs and two for iscsi.

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