[strongSwan] client to site but as a gateway(nat)?

Karl Denninger karl at denninger.net
Fri Jul 21 00:37:46 CEST 2017

On 7/20/2017 17:30, peljasz wrote:
> On 20/07/17 22:57, Karl Denninger wrote:
>> On 7/20/2017 16:46, peljasz wrote:
>>> On 20/07/17 21:57, Karl Denninger wrote:
>>>> That can be made to work provided you do not need inbound
>>>> connections to things on the client side.
>>> exactly like that.
>>> How to even phrase a query to find docs/howtos on such a setup?
>>> Or, tips on setup/config much appreciated - I have a working client
>>> to site setup - is it only strongswan or/and routing/nating outside
>>> of swan?
>>> many thanks.
>>> L
>> There's really nothing specific related to StrongSwan there other
>> than not mapping your own client NAT implementation on top of
>> whatever address/subnet the VPN gateway gives you.
>> Essentially your client is responsible for NATting the
>> client-attached traffic which is then sent to the VPN gateway, which
>> (presumably) will NAT it again.  It should work with few potential
>> issues (the big one being if you have a UDP client of some sort and
>> the intermediate NAT times out on stateful tables you'll lose some
>> replies, but this usually isn't much of a factor.)
>> This is, in essence, what running a Hotspot that is also a StrongSwan
>> client back to a server winds up being -- the VPN server is NATing
>> traffic to the Internet, and the Hotspot is NATing traffic for its
>> attached clients.  It should all "just work" in most cases.
> well, if I understand it correctly then my setup is a bit different,
> but I thought it still would be commonly desired that there would be
> many and easy to find howtos.
> Namely: a linux box with a public IP(not static per say but almost the
> same IP all the time) and that box is the default gateway/nat for
> local/home lan. Now that very box calls out(as a client) to a VPN's
> site(server I have no control over).
> What is working as of now:
> - linux box vpns out with rightsubnet= but the rest(from
> itself and home lan go out via linux nat(via my ISP)
> - from another node on local/home lan I can ping linux's vnp client
> IP(given by the swan server), on the node a added route to
> via's local lan IP which is the
> default gateway for local/home lan to the Internet via ISP)
> ! but I cannot reach anything else on from that same
> node that can ping client IP)
> what I want:
> a node(s) -> => the whole Internet
> (except to should go via linux's vpn client)
> something I am missing.
I'm not understanding the network topology in question... is the VPN
server on a separate connection from your general Internet ISP or is it
a site on the Internet (and thus transports down that connection)?

I suspect the issue is either (1) a routing one or (2) the packets
you're tossing down the VPN connection have not been NAT'd before they
go down the VPN and thus from the perspective of the server end they're
*not* coming from your attached host (which it knows how to reach) but
rather from a random address, which is private and
unrouteable (and thus getting tossed on the floor on the other end.)

Karl Denninger
karl at denninger.net <mailto:karl at denninger.net>
/The Market Ticker/
/[S/MIME encrypted email preferred]/
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