Cisco Networking – Is Network Configuration Possible with Layer 3 Switch and ISP Routers?


If possible I would like to use a Cisco SF350-24 Layer 3 switch to enable the below network layout. In our office we have 2 internet connections we often use for testing that require an internet connection. We would like a VLAN for each of them.

I am very new to Cisco switches but am able to setup VLAN configuration etc using packet tracer and some tutorials online. However, I'm not sure I can even achieve the below setup with 2 different networks and supplying the VLAN's with an internet connection using the same Layer 3 switch?

Any advice would be greatly appreciated
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With the L3 switch (Cisco 350 series) could I achieve the below? (Network 2 left in for continuity)

Network Layout Option 2

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Best Answer

In your schema the VLAN on the left, let's call it VLAN 10, is associated with subnet, while the VLAN on the right, which we will call VLAN 20, is associated with

So you need a gateway for each VLAN, and the only candidate is the switch. It is layer 3 so there's no issue here.

Now, the switch receives a packet from a computer in VLAN 10 for example. How does it know to which ISP router it should forward the packet?

To be able to choose the correct ISP you need to use either one of this features:

  • PBR - I.E. Policy Based Routing: allow to choose a route based on a specific criteria, like the source IP address.
  • VRF: maintains several (in our case 2) routing instances on the switch.
  • NAT: allow to transform the source IP addresses of VLAN 10 to a 192.168.1.X IP address and the source addresses of VLAN 20 to a 192.168.2.X IP address.

Unfortunately your chosen switch doesn't offer any of these features, so the answer is no, you cannot do it.

What you could do is use in VLAN 10 and in VLAN 20 (configuring the port that connect to the ISP router in access mode for the corresponding VLAN).

This would put the 3 PCs in each section in the same network though, I don't know if this suit your needs.