> Has anyone got a transparent proxy working on a router / firewall,
> in a similar way to how a transparent squid proxy is setup up with
> an ipchains port 80 redirect?
>
> (I want to capture all --dport 25 traffic coming out of a subnet,
> and force it all though the local mail server which I want to act as
> an outgoing relay host).
>
> Doing the actual port redirection is trivial, but my problem is in
> getting a local sendmail daemon to handle it in a sane way (it
> doesn't seem to work at all, or at least not how I think it should).
I don't have a working solution; here's how I would try to solve it
Deflect traffic to a test port on a test IP address,
Ron a sendmail daemon at one end, using -v (verbose) to log stuff, and invoke
sendmail at the other end, also using -v, to report on what it sees.
There's a lot of -d options to select logging too. Some of them may be useful;
read your sendmail book (or source code, I don't think they're detailed in the
softcopy documentation) to discover what they are.
If this fails to resolve the problem, then...
Keeping a careful eye on the relevant RFCs, write a small application in a
language of choice for exploring these things (I'd probably use Java, but perl
and C will both do the job) that would intercept the incoming traffic and
relay it to my test sendmail.
It would, of course, report everything to a log file, everything including the
control/protocol messages exchanged; you might not find the actual messages
useful.
This should lead to a resolution of the problem (and may well end up being
your proxy).
>
> [ apologies to ask this off-topic question here, I'd normally ask
> this somewhere like linux-config or linux-net, but I've yet to
> resubscribe to the vger lists since it has moved over to
> kernel.org ]
Sounds like a development issue to me.
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