Nico Schottelius wrote:- allow AH, ESP, UDP/500, deny rest on eth0 - allow IPs/networks, etc. on ipsec0
- allow hosts/networks on eth0 (in Netfilter part of kernel)
- setup IPSec policies so that traffic from allowed hosts/networks is required to be encrypted (in IPSec part of kernel)
One thing that just came to my mind. The unencrypted packet is obviously related to the encrypted packet. I don't know if IPSec part of kernel is aware of Netfilter part of kernel, and I have no idea how Netfilter (or kernel) is internally tracking packtes, but a thing to try (might work, or might fail misserably) in exactly this order:
- allow hosts/networks if state is RELATED - allow AH, ESP, UDP/500 if state is NEW or ESTABLISHED
Once again, I have no idea if your assumption that encrypted packtes are traversing Netfilter tables twice is correct, so above might just be me blabing about something I have no idea how it works. Consider this to well intended brainstorming (just some ideas from back of my head, that might not have any support in reality).
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