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I have two new 3850 24 port gig switches. I am putting one in the front wiring closet of our warehouse, the other in the rear.

IS there a way to have these be a layer 2 / layer 3 Virtual Switch using VSS?

I was looking at creating a cross-stack etherchannel. But didn't know what that really would do regarding layer 2/ layer 3 redundancy, if any. I have DHCP, a few VLANs, and inter vlan routing configured.

Was hoping that there was some way to do this so that if one switch failed, the other would still provide inter-vlan routing.

Let's say I have VLAN 2. I assign 3850-1 a port in VLAN 2 with IP 192.168.1.1.

Let's say I have 3850-2 and I have an ether channel.

If 3850-1 goes down, I want 3850-2 to be able to still route for VLAN 2 as the default gateway for that VLAN.

It's almost like having a virtual IP for the default gateway IPs for each VLAN and having one switch have the active role on it, and if that switch failes, to have the other switch take that VIP and continue to provide basic intervlan routing.

Perhaps put differently, how can I have the two switches provide inter-vlan routing redundancy?

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You can't do VSS with the 3850's. You could stackwise through the stacking ports but that would require them to be somewhat near eachother.

You can setup HSRP/VRRP/GLBP with a virtual IP to provide next hop redundancy. however, you would not be able to form a functional etherchannel from one device to both switches.

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  • OK. Thanks. I will look into that. My budget originally called for (4) 3850s. I was going to use stackwise to create two stacks, one in each wiring closet. BUt my budget got cut. So now I have one in each. I was hoping to provide routing redundancy somehow. but need etherchanels to trunk the switches together. Stackwise is what I was hoping to do. but they need to be close to each other. Are there other recommendations you'd do? I was thinking of using DHCP to send out two gateways, primary secondary, to clients. if one goes down, they could route to the other.
    – Bubbawny
    Jun 16, 2016 at 20:46
  • I already mentioned the alternative - HSRP
    – Rex
    Jun 21, 2016 at 22:26
  • Hi Rex: Can you advise why you can't have an etherchannel? I was going to have our servers have one port connected on each switch for redundancy (Switch Fault Tolerance). DOes this also mean you cannot have an etherchannel between the switches as well? i've bee scouring the internet about HSRP and etherchannels having this limitation but haven't found anything.
    – Bubbawny
    Jun 29, 2016 at 14:19
  • You can certainly do etherchannel between the two switches. I was saying you can't create an etherchannel group from the one device (server) to both switches.
    – Rex
    Jun 30, 2016 at 15:45
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So I ended up using an Etherchannel (ports 23/24 on each switch).

I setup VTP.

I setup HSRP for fail over routing. This was the key, as with trunks (dot1q). I have my servers running SFT between switches. This way, if one switch fails, I have routing, trunking, and core layer 2/3 capabilities. While it's not VSS, it's getting much of what I need done.

One day, when my budget expands, I'll add switches to each to create a redundant stack in the front and back wiring closets.

Lot to learn yet. But this is working for me.

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