I've been trying to find a way to implement a Layer 3 VPN without using MPLS. But I think I must but terrible at using Google, because I cant find any usable information. Everything I find uses MPLS.

Am I stupid? (Dont answer that )

If you can explain the requirement in more detail it would be easier to point you in a direction.

There are various ways to obtain VPN functionality without MPLS including PPTP, Open VPN, IPSEC, L2TP. Which if any is appropriate depends on the proposed application.

I am writing a report on why MPLS should be implemented or not, in an ISP environment. So I want to compare a VPN using MPLS with one that doesn't. Does that make sense?

I am not sure whether you were referring to a specific MPLS/BGP method of providing layer 3 VPN or layer 3 VPNs in general. Among companies and individuals the traditional VPN technologies are still in heavy use while carriers certainly make increasing use of MPLS/VPLS/VPRN etc. .

If looking at MPLS benefits in an ISP environment I would be looking at benefits beyond simple L3 VPN provisioning. At its heart MPLS is a packet switching mechanism which can provide its own performance efficiencies while additionally providing a lot of provisioning flexibility to the ISP when combined with the likes of VPLS/VPRN etc. .

There's no way to transport data using L3VPN without mpls, because you need to mark vpn4 on BGP address family settings. You can see all the routes propagated, but the communication is using mpls labels....so, MPLS is a must to use if you wanna create L3VPNs. I was doing a lab about L3VPNs and I forgot enable MPLS... results? I was seeing all the routes being propagated, all seemed right, only enabled MPLS settings and everything worked very well.

Have you considered a VRF-lite type network?

I had to go this way because MPLS wasn't working so well in my scenario. Admittedly, it involves a lot more manual steps; but I use it in production, so I know it works.

10,000ft overview:

1. Create a tagged-VLAN on inter-router interfaces
2. Create a VRF with the interfaces you want to have part of the VPN, include tagged-VLAN interfaces from step 1
3. Assuming you're using OSPF, create a new OSPF instance and tell the instance (under MPLS tab) to use VRF routing table from step 2
4. Bind OSPF to tagged-VLAN interfaces for route distribution

Caveats:
- You have to do those steps on EVERY router on the VPN path
- If your wireless bridges aren't VLAN-passive, you'll need to tell EVERY wireless bridge on the VPN path about the inter-router VLANS