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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 enter image description here

(Edit) With the L3 switch (Cisco 350 series) could I achieve the below? (Network 2 left in for continuity)

Network Layout Option 2

enter image description here

1 Answer 1

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In your schema the VLAN on the left, let's call it VLAN 10, is associated with subnet 192.168.10.0/24, while the VLAN on the right, which we will call VLAN 20, is associated with 192.168.20.0/24.

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 192.168.1.0/24 in VLAN 10 and 192.168.2.0/24 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.

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  • With that cheap switch type, you could simply use two of them, one for each site. Point each one's default gateway to the respective ISP router and use a static route between them.
    – Zac67
    Nov 11, 2021 at 10:13
  • Thank you for the responses. One option could be to use 2 Cisco switches. Another could be to scale back and simplify this and forget about the VLAN for Network 2 Then leave Network 2 connected directly to the router. Could another option be to add a router capable of one of the options above; policy based routing, VRF or NAT?
    – James N
    Nov 11, 2021 at 10:49
  • @JamesN If you use a single, central L3 switch (as gateway) but want to split WAN routes by source network, either PBR or VRF are required. If you remove the lower VLANs you can just the same omit the L3 switch and connect the routers directly.
    – Zac67
    Nov 11, 2021 at 11:01
  • @Zac67 Ok thanks. I have edited my question to include another option. Regarding the switch we have is this possible in your opinion? Potentially getting another switch to satisfy Network 2 with VLAN may be the best but I want ot be sure this will work with that switch
    – James N
    Nov 11, 2021 at 11:55
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    @JamesN Definitely. The L3 switch routes private-to-private and the ISP router routes private-to-public (and possibly vice versa). If you don't want full connectivity between all VLANs you can control/filter the traffic by ACLs on the switch.
    – Zac67
    Nov 11, 2021 at 12:05

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