if_ipsec

[Eugene M. Zheganin]

Hi.

I have an idea about new networking feature in FreeBSD.
I guess everyone is having ideas from time to time, and lots of these 
idea having people think that they just had a decent idea. However, only 
ideas that are complemented by a working code can be considered by the 
community, and only some of them got commited into the tree, I am fully 
aware of this fact.

Unfortunately, I am not able to produce the code. I guess this is the 
point where most of the subscribers will (or at least should) stop 
reading this post. Still, I'm addressing this post for people that have 
the time and will to do something interesting. I guess that someone may 
find this interesting. Myself, I find that this could be really useful.

(You can skip this part and the next part if you only want to read about 
the idea) I work about 10 years as a network engineer. My company holds 
country-wide supermarkets business. I am personally responsible for the 
network infrastructure of the company. As the company has lots of 
(hundreds) of branch offices, lots of my time I'm constructing new VPNs 
between them. My company network infrastructure is build using FreeBSD 
servers and Cisco (and last year - Juniper) equipment. So I am aware and 
capable of building VPN of almost any modern type, and this is the post 
about building it on FreeBSD (this annoying passage was written to give 
you impression that I'm not just a guy with FreeBSD server at home, 
holding a couple of movies).

So. About VPNs. Another annoying passage about common ways and caveats. 
Otherwise most of the reading ppl will say 'Why the hell if_ipsec ?' 
(ppl that are aware of the VPNs can really skip this part). The 
conventional way to build vpn is to build a tunnel of some sort. This 
can be an encrypted tunnel, or an unencrypted tunnel. Unencrypted 
tunnel  (gre/ipinip) is obviously unencrypted, but gives you an 
interface which could be using in routing. Encrypted tunnel (and I'm 
talking about ipsec) cannot be used for rounting, but is encrypted. 
Plus, you have to care about policies, and when multiple routers are 
involved, with hundreds of networks behind them, you have to care about 
tonns of policies, and this is painful. So, the industry invented a 
method: you use a gre/ipinip tunnel, you pass the dynamic routing 
information (you don't care bout networks, you only care abouth the 
endpoints), and you encrypt this tunnel with ipsec. So, gre + ipsec (of 
gif + ipsec). This way is supported by all of the major vendors, you can 
build gre(ipinip)+ipsec tunnel to any Cisco/Juniper device. Though 
building in to JunOS requires some skill and a deep knowledge. :)

(here the idea starts) But what is an gre or gif tunnel ? This is not an 
interface, but a way to tell the system, that it needs to encapsulate 
some of the payload with another header, and send it somewhere. So, 
using ipsec you add an extra header, and using gre(ipinip) you add an 
extra header. What if we will add an additional ability to understand 
that some of the ipsec packets are destined to the security gateway 
(which adds the extra header) itself,  like it's possible with 
gre/ipinip, so we can get rid of one extra header ? Cisco/Juniper did 
that. So, Cisco has the 'tun mode ipsec ipvX' interface, and Juniper has 
the st (secure tunnel) interface. How does it work: it's a convenstional 
ISAKMP  IPsec with the ability to treat some of the packets with a 
particular IP like destined to the local (by this I mean 'this') host. 
Besides this it's the old IPsec. It's even interoperable between 
different vendors devices. I don't see any reason why FreeBSD cannot 
have this ability, since it does have a working Ipsec and working 
ISAKMP. In order to obtain this functionality FreeBSD needs to have a 
way to define the templates for the SPD entries, and  the way to create 
these SPD entries after the creation of the interface, based on it's 
address information. This will really simplify the VPN creating and 
management.

So... here was the idea. :)
It came to my head after configuring the Juniper/Cisco VPN (and the 
config was really short), and after reading quagga-users@ maillist, 
where some of the subscribers asked about 'tun mode ipsec'. Plus, as far 
as I know, Linux does not support this too, so we could really score 
some points.

Eugene.