[ILUG] proxy

[kevin lyda]

kilmartin mark wrote:
> Can anybody point me to a simple HOWTO/guide to setting up a linux machine
> to act as a proxy server for a small network.
> The linux machine if fitted with an external modem for dialup Internet
> connection.
> 
> I have looked at a number of documents but each one seems to give a
> different method of setting this up.

add this to /etc/rc.d/rc.local (i'm assuming a redhat setup for the file
name of the rc script, but the commands should work for any 2.2.x box,
and most init scripts have something like rc.local)

	ipchains -P forward DENY
	ipchains -A forward -i ppp0 -j MASQ
	echo 1 > /proc/sys/net/ipv4/ip_forward

there's some file in /etc/sysconfig (network?) that has a FORWARD= line
or something like it that would obviate the need for the last line.  if
you have a cable modem you'd really make me depressed and you'd need to
do a s/ppp0/ethN/ where N is the interface hooked up to the cable modem.

by the way for folks drooling over cable modems i should mention the
following issues to look out for:

  o they usually "key" the "modem" to your MAC address so you'll
    need to always use that card.
  o be very paranoid about that interface.  make a conscious decision
    to find automatic package update tools sexy and learn how to
configure
    them.  run tripwire.  strip the box of useless crap and note that a
486
    will more than handle the load - consider using something from a
mini-linux
    group like the lrp.
  o no, really, be security aware.
  o consider openbsd.
  o put two interfaces in the box.  don't cheat and plug the cable modem
into
    a hub, the router in the hub, and your other machines on the hub.  i
know
    people that lost their cable modem access in the states.  consider
not
    letting the installers see: linux, any signs of a home network, or
the
    second nic.
  o i'm serious about that security thing.  i wouldn't be surprised if
the
    DoS attack is being mounted from boxes on cable modem networks with
lax
    security (good morning mr. linux pr disaster, how are you today...).

kevin
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