Mixxing L2 & L3 Switches? Can We Still Use A Stack?

We currently have 1 switch on our network, it is a L2, Dell Powerconnect 3548P. We have 2 VLANs setup, and our Sonicwall Gateway/ Router does all the inter-vlan routing.

We utilize 1 VLAN for DATA and 1 VLAN for VOICE. Currently we get some "jitter" in the calls, i think due to the sonicwall having to route all the VLAN traffic and getting overwhelmed.

We are out of spots on our 3548P, and need to add another switch. Would the best route be to add a Dell Powerconnect 6224P L3 switch, which would allow all the inter-VLAN traffic to be routed at the switch level, and just allow the sonicwall to act as the external gateway?

Will the 3548P, and 6224P work together in a stack configuration, or do they have to be like models?

What other caveats would there be to a setup as such?
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carlson777Connect With a Mentor Commented:
How are things going?  Was your question answered?  Appears so.
I have not used Dells equipment, but you should not have any issues connecting.
- Create the same two vlans on Powerconnect 6224P L3 as on the 3548P and route between the two.
- Connect vlan a of 6224 to vlan a of 3548 via cross-over cable
- Connect vlan b of 6224 to vlan b of 3548 via cross-over cable
Fairly standard.
- This creates multiple single points of failure, but if you only have a single switch you currently have that now.
- Why not just get a 48 port layer 3 switch and replace the current layer 2 switch.  One less piece of equipment to work with.
HADDADD3Author Commented:
We need more then 48 ports... Our 48 port is filled, and we need about 10 more ports. We also have the problem with jitter on some calls, which i think is related to the sonicwall having to route all of the inter vlan traffic.
Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

It will work as you have designed without any issues, but I would suggest buying and additional 3548

Use the L2 switches for workstations, access layer switches, and the L3 switch for routing and servers the distribution/core layer of the network.  Cost is only an additional L2 switch approx $600 and you will have a cleaner design that allows you to make easier future design changes.
HADDADD3Author Commented:
Currently everything is on the L2 switch.

The proposed structure above would move all of the servers, and VoIP phones onto the L3 switch. Will the VoIP phones still benefit from the faster L3 switching throughput if they still resides on the L2 switch?
Issue most likely was the firewall processing each packet.  Removing the FW should address the issue.  Assume switches are PoE to lite up the phones.  With this size network bandwidth contention is not going to be your issue.  L2s are 100 Mbps with Gb uplink.  You should not have any problems.

You could also setup this way.
- Keep with just buying L3
- Connect L3 switch to both Gb uplinks of L2 using port-channel.  This would provide 2 Gb bandwidth between the two switchs.  Make the port channel a VLAN trunk allowing both VLANs over the trunk.  This way you are using the L3 SW for routing and provide 2 Gb for this task.  If need be in the future you can buy another L2 swtich and do same thing when adding it to the network if you don't want to buy an additonal switch.
- VOIP does not require 1 Gb ports which I think the 6224 provides but you could use these ports for this.
HADDADD3Author Commented:
So as i understand correctly:

All the devices now can stay where they are, I would connect the L3 switch using crossover cable on the GB uplink between the switches. The uplink port between the two switches would be a port, and on the L3 switch this would be set as a VLAN trunk.

How would the L3 switch then connect to the Sonicwall? If i am correct the Sonicwall would be the gateway of the L3 switch, so if the L3 switch does not know where to send the packet, it forwards it to the gateway, correct?

I would delete the VLAN trunks off the sonicwall, correct?

The ports on both switches would need to be trrunked.  A trunk port will only talk to another trunk port.
Do not know the exact commands on Dell switches, but create trunk port on L3 switch and L2 switch connect via cross over cable.  All the two VLANs you have created to use the trunk.

I would create a third VLAN on the L3 switch (not allowed over the trunk) using a /29 network.  Assign on IP to the L3 switch and firewall on this new network.  Only these two devices would currently talk on this network.  Default gateway for the switch would be new firewall address.  And yes would remove trunk from firewall.  If dell L3 switches allows you could instead of third vlan assign a switch port an IP address use /30 subnet and create a point to point link between fw and L3 sw.
HADDADD3Author Commented:
Just got the switch in, will keep you updated....
HADDADD3Author Commented:

I am having some difficultly configuring the 6224 switch.

How would I configure the trunk coming in from the 3248 switch, and how would the 6224 then be configured to interface with the sonicwall?

The network is currently setup:
Address:, Sonicwall acts as DHCP server for entire network

Management IP:
Default Gateway:

Management IP:
Default Gateway:

Data VLAN ID1:
Voice VLAN ID2:

The 3248 assigns packets to the voice VLAN using MAC address filtering, (Dynamic voice vlan) whereby if the mac address matches know VoIP phone MACs it adds tagged packets into the VLAN ID2, it ages them out after 48 hours.

No phones will be plugged into the 6224, which should simplify things.
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