Date: Sun, 19 Nov 2000 15:11:32 -0500 From: Sam Carleton <scarleton@bigfoot.com> To: "security@FreeBSD.ORG" <security@FreeBSD.ORG> Subject: Re: help setting up a filewall Message-ID: <3A1833F4.A2A25FBC@bigfoot.com> References: <3A16C44B.4DEC2492@bigfoot.com> <20001118155447.K9740@149.211.6.64.reflexcom.com>
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"Crist J . Clark" wrote:
> > * In the article, it looks like the author is allowing things like HTTP
> > and SSH to come into the firewall machine. I want those things to be
> > passed onto another internal machine.
>
> The rules may or may not change depending on where they are relative
> to the divert(4) rule. Also, see 'redirect_address' and
> 'redirect_port' in natd(8). You did not post your natd.conf, so I
> can't tell if you are already using those.
Sorry about that, this time I will including EVERYTHING :)
> > Attached you will find my modifications to the rc.firewall script and
> > relavent snips of rc.conf. If you have any thoughts on what I am doing
> > wrong, please drop me an email. Thanks!
>
> A few nitpicks about your ruleset, but nothing absolutely leaped out
> at me as a problem that would totally break everything. Since you did
> not tell us exactly what kind of problem you are having, it's hard to
> know what to look for.
Well, the problem I am currently having is with DNS. The test enviornment that I have setup is such that
there is no DNS server behind the FreeBSD firewall. The machine inside the firewall is not able to get a
DNS request out. To make things more interesting, while booting the FreeBSD firewall, the rc.firewall
script ALWAYS hangs on the two DNS lines.
# Allow DNS queries out in the world
${fwcmd} add pass udp from ${iif} to any 53 keep-state
${fwcmd} add pass tcp from ${iif} to any 53 keep-state
The setup I am looking for is one where anyone on the inside can get to any DNS server on the outside. I
am going to have one caching DNS server on the inside, but if that is down, the clients will be configured
to goto a DNS server outside the firewall. What rules would you setup for this configuration?
This is what I have currently:
-----------rc.conf-----------
gateway_enable="YES"
hostname="orchid.miltonstreet.com"
ifconfig_ep0="DHCP"
ifconfig_xl0="inet 192.168.100.6 netmask 255.255.255.0"
inetd_enable="Yes"
moused_enable="YES"
nisdomainname="NO"
router_enable="No"
saver="fire"
sendmail_enable="NO"
sshd_enable="NO"
usbd_enable="YES"
firewall_enable="Yes"
firewall_type="Simple"
firewall_script="/etc/rc.firewall"
firewall_quite="No"
natd_program="/sbin/natd"
natd_enable="Yes"
natd_interface="ep0"
natd_flags="-f /etc/natd.conf"
-----------natd.conf-----------
dynamic yes
use_sockets yes
same_ports yes
-----------rc.firewall-----------
############
# Setup system for firewall service.
# $FreeBSD: src/etc/rc.firewall,v 1.30.2.4 2000/05/28 19:17:15 asmodai Exp $
# Suck in the configuration variables.
if [ -r /etc/defaults/rc.conf ]; then
. /etc/defaults/rc.conf
source_rc_confs
elif [ -r /etc/rc.conf ]; then
. /etc/rc.conf
fi
############
# Define the firewall type in /etc/rc.conf. Valid values are:
# open - will allow anyone in
# simple - will try to protect a whole network
# closed - totally disables IP services except via lo0 interface
# UNKNOWN - disables the loading of firewall rules.
# filename - will load the rules in the given filename (full path required)
#
# For ``simple'' the entries below should be customized
# appropriately.
############
#
# If you don't know enough about packet filtering, we suggest that you
# take time to read this book:
#
# Building Internet Firewalls
# Brent Chapman and Elizabeth Zwicky
#
# O'Reilly & Associates, Inc
# ISBN 1-56592-124-0
# http://www.ora.com/
#
# For a more advanced treatment of Internet Security read:
#
# Firewalls & Internet Security
# Repelling the wily hacker
# William R. Cheswick, Steven M. Bellowin
#
# Addison-Wesley
# ISBN 0-201-6337-4
# http://www.awl.com/
#
if [ -n "${1}" ]; then
firewall_type="${1}"
fi
############
# Set quiet mode if requested
#
case ${firewall_quiet} in
[Yy][Ee][Ss])
fwcmd="/sbin/ipfw -q"
;;
*)
fwcmd="/sbin/ipfw"
;;
esac
############
# Flush out the list before we begin.
#
${fwcmd} -f flush
############
# These rules are required for using natd. All packets are passed to
# natd before they encounter your remaining rules. The firewall rules
# will then be run again on each packet after translation by natd,
# minus any divert rules (see natd(8)).
#
case ${natd_enable} in
[Yy][Ee][Ss])
if [ -n "${natd_interface}" ]; then
${fwcmd} add 50 divert natd all from any to any via ${natd_interface}
fi
;;
esac
############
# If you just configured ipfw in the kernel as a tool to solve network
# problems or you just want to disallow some particular kinds of traffic
# then you will want to change the default policy to open. You can also
# do this as your only action by setting the firewall_type to ``open''.
#
# ${fwcmd} add 65000 pass all from any to any
############
# Only in rare cases do you want to change these rules
#
${fwcmd} add 100 pass all from any to any via lo0
${fwcmd} add 200 deny all from any to 127.0.0.0/8
# If you're using 'options BRIDGE', uncomment the following line to pass ARP
#${fwcmd} add 300 pass udp from 0.0.0.0 2054 to 0.0.0.0
# Prototype setups.
#
case ${firewall_type} in
[Oo][Pp][Ee][Nn])
${fwcmd} add 65000 pass all from any to any
;;
[Ss][Ii][Mm][Pp][Ll][Ee])
############
# This is a prototype setup for a simple firewall. Configure this
# machine as a named server and ntp server, and point all the machines
# on the inside at this machine for those services.
############
# set these to your outside interface network and netmask and ip
oif="ep0"
# onet="192.0.2.0"
# omask="255.255.255.240"
# oip="192.0.2.1"
# set these to your inside interface network and netmask and ip
iif="xl1"
inet="192.168.100.0"
imask="255.255.255.0"
iip="192.168.100.6"
# Stop spoofing
${fwcmd} add deny all from ${inet}:${imask} to any in via ${oif}
# ${fwcmd} add deny all from ${onet}:${omask} to any in via ${iif}
# allow DHCP stuff
${fwcmd} add pass udp from any 67 to any 68 in via ${oif}
${fwcmd} add pass udp from any 68 to any 67 out via ${oif}
# Stop RFC1918 nets on the outside interface
${fwcmd} add deny log all from 10.0.0.0/8 to any via ${oif}
${fwcmd} add deny log all from any to 10.0.0.0/8 out via ${oif}
${fwcmd} add deny log all from 172.16.0.0/12 to any via ${oif}
${fwcmd} add deny log all from any to 172.16.0.0/12 out via ${oif}
# ${fwcmd} add deny log all from 192.168.0.0/16 to any via ${oif}
# ${fwcmd} add deny log all from any to 192.168.0.0/16 out via ${oif}
# Stop draft-manning-dsua-01.txt nets on the outside interface
${fwcmd} add deny log all from 0.0.0.0/8 to any via ${oif}
${fwcmd} add deny log all from any to 0.0.0.0/8 via ${oif}
${fwcmd} add deny log all from 169.254.0.0/16 to any via ${oif}
${fwcmd} add deny log all from any to 169.254.0.0/16 via ${oif}
${fwcmd} add deny log all from 192.0.2.0/24 to any via ${oif}
${fwcmd} add deny log all from any to 192.0.2.0/24 via ${oif}
${fwcmd} add deny log all from 224.0.0.0/4 to any via ${oif}
${fwcmd} add deny log all from any to 224.0.0.0/4 via ${oif}
${fwcmd} add deny log all from 240.0.0.0/4 to any via ${oif}
${fwcmd} add deny log all from any to 240.0.0.0/4 via ${oif}
# Allow TCP through if setup succeeded
${fwcmd} add pass tcp from any to any established
# Allow IP fragments to pass through
${fwcmd} add pass all from any to any frag
# HTTP - Allow access to our web server
${fwcmd} add pass tcp from any to any 80 setup
# SMTP - Allow access to sendmail for incoming e-mail
${fwcmd} add pass tcp from any to any 25 setup
# FTP - Allow incoming data channel for outgoing connections,
# Reject&Log all incoming control connections
${fwcmd} add pass tcp from any 20 to any 1024-65535 setup
${fwcmd} add deny log tcp from any to any 21 in via ${oif} setup
# SSH Login - Allow & Log all incoming
${fwcmd} add pass log tcp from any to any 22 in via ${oif} setup
# IDENT - Reset incoming connections
${fwcmd} add reset tcp from any to any 113 in via ${oif} setup
# Reject&Log all setup of incoming connections from the outside
${fwcmd} add deny log tcp from any to any in via ${oif} setup
# Allow DNS queries out in the world
${fwcmd} add pass udp from ${iif} to any 53 keep-state
${fwcmd} add pass tcp from ${iif} to any 53 keep-state
# Allow setup of any other TCP connection
${fwcmd} add pass tcp from any to any setup
# Allow NTP queries out in the world
${fwcmd} add pass udp from any 123 to any 123 via ${oif}
${fwcmd} add pass udp from any 123 to any via ${iif}
${fwcmd} add pass udp from any to any 123 via ${iif}
# TRACEROUTE - Allow outgoing, but not incoming
${fwcmd} add pass udp from any to any 33434-33523 out via ${oif}
### ICMP RULES
# ICMP packets
# Allow all ICMP packets on internal interface
${fwcmd} add pass icmp from any to any via ${iif}
# Allow outgoing pings, but not incoming
${fwcmd} add pass icmp from any to any icmptypes 8 out via ${oif}
${fwcmd} add pass icmp from any to any icmptypes 0 in via ${oif}
# Allow Destination Unreachable, Source Quench, Time Exceeded, and Bad Head
${fwcmd} add pass icmp from any to any icmptypes 3,4,11,12 via ${oif}
# Deny the rest of them
${fwcmd} add deny icmp from any to any
# Everything else is denied by default, unless the
# IPFIREWALL_DEFAULT_TO_ACCEPT option is set in your kernel
# config file.
;;
[Uu][Nn][Kk][Nn][Oo][Ww][Nn])
;;
*)
if [ -r "${firewall_type}" ]; then
${fwcmd} ${firewall_flags} ${firewall_type}
fi
;;
esac
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