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First off, this is a purely hypothetical, academic question. It's not intended for a real implementation. It should be clear that, for practical reasons, this is just overkill.

Let's assume I don't trust my own LAN peers, because there is a network hub (not switch) and anyone can listen to my ethernet frames, or because there is a rogue network admin that might be trying to mirror my ethernet port, or because I fear WPA KRACK.

Is it possible to set up IPSec in such a way that traffic between a host and a router is encrypted? That is, a host will encrypt traffic before sending it to a router, which the router will then decrypt and forward regularly to whatever internet host it should route to.

I know traffic can be encrypted between two routers to form a site-to-site VPN, or between two hosts, or between a host and a remote site. But in all these cases, there is a specific target IP address or router where the IPSec configuration can be targeted to.

When routing traffic over a default gateway, the router's IP plays no part: it's the remote host's address that's used, with the gateway's MAC address. So I don't understand if it's possible to set up IPSec in this way.

I know it is possible, however, to do it in another way: use a /30 for each client and treat your connection as a typical "road warrior" to a virtual LAN address space in the router's routing table, and set up IPSec to use the /30 IPs for IPSec endpoints. Or probably use PPTP, L2TP or even PPPoE with layer-2 encryption.

What I want to know if it's possible to have a typical /24 where hosts can maybe use Opportunistic Encryption to talk to each other, but also have the default gateway traffic encrypted.

closed as off-topic by Tim Brigham, MadHatter, yagmoth555, womble Oct 19 '17 at 5:05

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Often, VPN connections use "split tunnelling" ie. only a specific subnet (or several) are routed through the tunnel.

Without split tunnelling, all your traffic is routed through the tunnel and all traffic is encrypted - the default gateway is set to the far side of tunnel. Your VPN gateway is likely to be a router, obviously you'll need to be allowed Internet access through it.

VPN is also a common method to increase wi-fi security and solves the WPA2 weakness just discovered.

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