If you have SPD rule (sorry for racoon/setkey speak)
0.0.0.0/0 Your.IP/32 any -P in esp/.../require (or unique)
then any packet coming to your box which is not esp encapsulated will be thrown away by ipsec code in kernel (if I remember correctly, it will not even reach FORWARD chain). Therefore you could safely skip check for esp, ah, udp/500 in iptables rules.
P.S. you may need to add SPD rule allowing udp/500 before enforcing esp traffic. I never required to ipsec all the traffic and therefore I'm not sure on this detail.
Nico Schottelius wrote:
Hello Pablo,
(netfilter guys, please read http://www.uwsg.iu.edu/hypermail/linux/net/0405.0/0002.html before)
Pablo Neira [Mon, May 03, 2004 at 01:48:15PM +0200]:
Hi Nico,
since this stuff is netfilter-related and netfilter/iptables geeks are mostly in netfilter's maillist, I think you could redirect this request there, someone could help you out.
Thank you for the hint. I first thought this is a netfilter problem, but currently I don't think so.
The problem is IMHO the design of the Linux IPSec implementation.
I'll compare what freeswan did with what Linux 2.6 does now:
Freeswan has virtual devices (ipsec*), through which the unencrypted packets come into the system. So you can add these firewall lines:
- allow AH, ESP, UDP/500, deny rest on eth0 - allow IPs/networks, etc. on ipsec0
With Linux 2.6 I don't have virtual devices. This means that my IPSec packets enter the physical device twice:
1. esp encrypted packet enters 2. Linux decrypts it 3. Linux sends the unencrypted packets through the same device again
The problem with that is, that
- allow AH, ESP, UDP/500, deny rest on eth0
will deny the _content_ of my encrypted packages (step three is broken).
Wouldn't this work fine, if we have the virtual device like freeswan had or is netfilter broken with this?
I mean I cannot practicly setup an IPSec only access point with the current netfilter and ipsec in Linux 2.6, or am I deadly wrong?
Greetings,
Nico
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