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7.2 KiB
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178 lines
7.2 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9">
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<TITLE>Diald Howto: Connecting a proxy/firewall to an ISP using a modem and PPP</TITLE>
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<LINK HREF="Diald-HOWTO-9.html" REL=next>
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<LINK HREF="Diald-HOWTO-7.html" REL=previous>
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<LINK HREF="Diald-HOWTO.html#toc8" REL=contents>
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</HEAD>
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<BODY>
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<A HREF="Diald-HOWTO-9.html">Next</A>
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<A HREF="Diald-HOWTO-7.html">Previous</A>
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<A HREF="Diald-HOWTO.html#toc8">Contents</A>
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<HR>
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<H2><A NAME="s8">8. Connecting a proxy/firewall to an ISP using a modem and PPP</A></H2>
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<P>
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<P>Connecting a private net to the Internet with dedicated server which
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handles packet routing from the local network to the Internet along with
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proxy/caching services and security firewalling is a complex theme that is
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beyond the scope of this document. There are other <20>Howto<74> documents that
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handle these topics much more comprehensively. At the end of this
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document you can find a list of links and references to such documents.
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<P>Here, we are only configuring <EM>Diald</EM> supposing that the computer
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already uses IP-Masquerading, has a web proxy like <EM>Squid</EM> or similar
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working, an ISP connection correctly configured and that access security
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to TCP/UDP ports have been revised (<CODE>/etc/inetd.conf</CODE> file and
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others like <CODE>securetty</CODE>, <CODE>host.allow</CODE>, etc).
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<P>Basically, the only need is to reconfigure the rules for
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masquerading/filtering/accessing each time the set of interfaces change,
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that is, when the interface ppp0 is stablished and when it is deleted. A
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good location to do that are the ip-up and ip-down scripts from <EM>pppd</EM>.
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<P>
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<H2><A NAME="ss8.1">8.1 Example for Debian 2.1</A>
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</H2>
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<P>
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<P>With Debian, it is sufficient to install the <EM>ipmasq</EM> package answering
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that you want to change rules sinchronously with <EM>pppd</EM> when seting it
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up. Two scripts will be created inside <CODE>/etc/ppp/ip-up.d</CODE> and
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<CODE>/etc/ppp/ip-down.d</CODE> directories to call <CODE>/sbin/ipmasq</CODE>, a
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script that analizes existing interfaces and makes a simple configuration
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that is valid in many cases, but you can personalize it using rule files
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in <CODE>/etc/ipmasq/rules</CODE>.
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<P>The only correction after installing this package is to change when the
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startup script for <EM>ipmasq</EM> is run, deleting the symbolic link from
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<CODE>/etc/rcS.d</CODE> and creating a new one in <CODE>/etc/rc2.d</CODE> to run
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it after <CODE>S20diald</CODE>. Now, when <CODE>ipmasq</CODE> is executed to analyze
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interfaces <CODE>sl0</CODE> already exist. <CODE>S90ipmasq</CODE> is a good name for this
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symbolic link to <CODE>/etc/init.d/ipmasq</CODE>.
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<P>Using Debian there is no need to worry about the kernel version, as the
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<CODE>/sbin/ipmasq</CODE> script uses <CODE>ipfwadm</CODE> or <CODE>ipchains</CODE> as
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needed.
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<P>
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<H2><A NAME="ss8.2">8.2 Example for Suse 6.1</A>
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</H2>
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<P>
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<P>This example is from Mr Cornish Rex, <CODE>
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<A HREF="mailto:troll@tnet.com.au">troll@tnet.com.au</A></CODE>.
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<P>The following ip-masp and routing control commands are for use with
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version 2.2 kernels, using ipchains, but they are not valid for version
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2.0 kernels.
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<P>We are going to supose that the ethernet interface has the 192.168.1.1 ip
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address with 16 bit netmask, that is, 255.255.0.0.
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<P>This is the <CODE>/etc/ppp/ip-up</CODE> file:
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<P>
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<BLOCKQUOTE><CODE>
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<PRE>
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#!/bin/sh
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# $1 = Interface
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# $2 = Tty device
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# $3 = speed
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# $4 = local ip
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# $5 = remote ip
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# $6 = ipparam
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/sbin/ipchains -F input
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/sbin/ipchains -P input DENY
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/sbin/ipchains -A input -j ACCEPT -i eth0 -s 192.168.0.0/16 -d 0.0.0.0/0
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/sbin/ipchains -A input -j DENY -p udp -i $1 -s 0.0.0.0/0 -d $4/32 0:52 -l
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/sbin/ipchains -A input -j DENY -p udp -i $1 -s 0.0.0.0/0 -d $4/32 54:1023 -l
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/sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 0:112 -l
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/sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 114:1023 -l
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/sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 6000:6010 -l
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/sbin/ipchains -A input -j DENY -p icmp --icmp-type echo-request \
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-i $1 -s 0.0.0.0/0 -l
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/sbin/ipchains -A input -j DENY -p icmp -f -i $1 -s 0.0.0.0/0 -l
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/sbin/ipchains -A input -j DENY -p udp -i $1 -s 0.0.0.0/0 -d $4/32 5555 -l
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/sbin/ipchains -A input -j DENY -p udp -i $1 -s 0.0.0.0/0 -d $4/32 8000 -l
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/sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 8000 -l
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/sbin/ipchains -A input -j DENY -p udp -i $1 -s 0.0.0.0/0 -d $4/32 6667 -l
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/sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 6667 -l
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/sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 4557 -l
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/sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 4559 -l
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/sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 4001 -l
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/sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 2005 -l
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/sbin/ipchains -A input -j DENY -p tcp -i $1 -s 0.0.0.0/0 -d $4/32 6711 -l
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/sbin/ipchains -A input -j DENY -i $1 -s 192.168.0.0/16 -d 0.0.0.0/0 -l
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/sbin/ipchains -A input -j ACCEPT -i $1 -s 0.0.0.0/0 -d $4/32
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/sbin/ipchains -A input -j ACCEPT -i lo -s 0.0.0.0/0 -d 0.0.0.0/0
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/sbin/ipchains -A input -j DENY -s 0.0.0.0/0 -d 0.0.0.0/0 -l
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/sbin/ipchains -F output
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/sbin/ipchains -P output DENY
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/sbin/ipchains -A output -j ACCEPT -i eth0 -s 0.0.0.0/0 -d 192.168.0.0/16
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/sbin/ipchains -A output -j DENY -i $1 -s 192.168.0.0/16 -d 0.0.0.0/0 -l
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/sbin/ipchains -A output -j ACCEPT -i $1 -s $4/32 -d 0.0.0.0/0
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/sbin/ipchains -A output -j ACCEPT -i lo -s 0.0.0.0/0 -d 0.0.0.0/0
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/sbin/ipchains -A output -j DENY -s 0.0.0.0/0 -d 0.0.0.0/0
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/sbin/ipchains -F forward
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/sbin/ipchains -P forward DENY
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/sbin/ipchains -M -S 120 120 120
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/sbin/ipchains -A forward -j MASQ -s 192.168.1.0/24
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/sbin/ipchains -A forward -j DENY -s 0.0.0.0/0 -d 0.0.0.0/0
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exit 0
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>This is the <CODE>/etc/ppp/ip-down</CODE> file:
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<P>
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<BLOCKQUOTE><CODE>
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<PRE>
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#!/bin/sh
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# $1 = Interface
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# $2 = Tty device
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# $3 = Speed
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# $4 = Local ip
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# $5 = Remote ip
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/sbin/ipchains -F input
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/sbin/ipchains -F output
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/sbin/ipchains -F forward
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/sbin/ipchains-restore < /etc/ppp/orig.chains
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>Last file in last script, orig.chains, is the following file (original
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status of ipchains):
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<P>
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<BLOCKQUOTE><CODE>
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<PRE>
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# orig.chains
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# created with: ipchains-save > orig.chains
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:input ACCEPT
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:forward ACCEPT
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:output ACCEPT
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-A input -s 0.0.0.0/0.0.0.0 -d 192.168.1.1/255.255.255.255
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-A output -s 192.168.1.1/255.255.255.255 -d 0.0.0.0/0.0.0.0
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>
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<H2><A NAME="ss8.3">8.3 Example for Slackware 3.6</A>
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</H2>
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<P>
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<P>This example is from Hoo Kok Mun, <CODE>
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<A HREF="mailto:hkmun@pacific.net.sg">hkmun@pacific.net.sg</A></CODE>.
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<P>This is the most simple example i have seen, but fully functional. From
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the beginning, this example configures masquerading, before the <CODE>sl0</CODE>
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interface exists, and it does not change when the <CODE>ppp0</CODE> interface
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appears. If you need advanced security considerations, it may be a little
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limited.
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<P>
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<BLOCKQUOTE><CODE>
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<PRE>
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#/etc/rc.d/rc.local
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/sbin/ipfwadm -F -p deny
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/sbin/ipfwadm -F -a m -S 192.168.0.0/24 -D 0.0.0.0/0
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>As you can see, it is for version 2.0 kernels.
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<P>
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<HR>
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<A HREF="Diald-HOWTO-9.html">Next</A>
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<A HREF="Diald-HOWTO-7.html">Previous</A>
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<A HREF="Diald-HOWTO.html#toc8">Contents</A>
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</BODY>
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</HTML>
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