Re: IPFW via command problem

imoore Sun, 14 Dec 2003 00:49:06 -0800

Jaime writes:

On Sunday, December 14, 2003, at 01:49 AM, Ian Moore wrote:
# Allow outgoing pings ${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}

where I have defined ${oif} as oif="xl1" where xl1 is my external interface

The above lines don't allow pings to the outside world, but if I comment out via ${oif} then it does allow them.
I'd have to know more about your firewall to be certain, but it looks kind of like you've over-looked the IFPW rules that would be needed by your internal interface. If the external interface allows pings but the internal doesn't, then it won't let pings pass through the box. They will be stopped at the internal interface on their way from your internal workstation to the firewall.

Hope that helps, Jaime

Perhaps I should have posted the whole script, though you can see it at the web site I mentioned. There is a rule just before those 2 to allow icmp on the internal interface: # Allow all ICMP packets on internal interface ${fwcmd} add pass icmp from any to any via ${iif}

Here is my config in full, except for the external address & dns addresses:

# 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

if [ -n "${1}" ]; then firewall_type="${1}" fi

# Firewall program fwcmd="/sbin/ipfw"

# Outside interface network and netmask and ip oif="xl1" onet="x.x.x.0" omask="255.255.255.0" oip="x.x.x.y"

# Inside interface network and netmask and ip iif="xl0" inet="192.168.0.0" imask="255.255.255.0" iip="192.168.0.9"

# My ISP's DNS servers dns1="z.z.z.z" dns2="y.y.y.y"

# Flush previous rules ${fwcmd} -f flush

# Allow loopbacks, deny imposters ${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

# 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}

# Stop RFC1918 nets on the outside interface ${fwcmd} add deny all from any to 10.0.0.0/8 via ${oif} ${fwcmd} add deny all from any to 172.16.0.0/12 via ${oif} ${fwcmd} add deny all from any to 192.168.0.0/16 via ${oif}

# Stop draft-manning-dsua-03.txt (1 May 2000) nets (includes RESERVED-1, # DHCP auto-configuration, NET-TEST, MULTICAST (class D), and class E) # on the outside interface ${fwcmd} add deny all from any to 0.0.0.0/8 via ${oif} ${fwcmd} add deny all from any to 169.254.0.0/16 via ${oif} ${fwcmd} add deny all from any to 192.0.2.0/24 via ${oif} ${fwcmd} add deny all from any to 224.0.0.0/4 via ${oif} ${fwcmd} add deny all from any to 240.0.0.0/4 via ${oif}

# Network Address Translation. This rule is placed here deliberately # so that it does not interfere with the surrounding address-checking # rules. If for example one of your internal LAN machines had its IP # address set to 192.0.2.1 then an incoming packet for it after being # translated by natd(8) would match the `deny' rule above. Similarly # an outgoing packet originated from it before being translated would # match the `deny' rule below. ${fwcmd} add divert natd all from any to any via ${natd_interface}

# Stop RFC1918 nets on the outside interface ${fwcmd} add deny all from 10.0.0.0/8 to any via ${oif} ${fwcmd} add deny all from 172.16.0.0/12 to any via ${oif} ${fwcmd} add deny all from 192.168.0.0/16 to any via ${oif}

# Stop draft-manning-dsua-03.txt (1 May 2000) nets (includes RESERVED-1, # DHCP auto-configuration, NET-TEST, MULTICAST (class D), and class E) # on the outside interface ${fwcmd} add deny all from 0.0.0.0/8 to any via ${oif} ${fwcmd} add deny all from 169.254.0.0/16 to any via ${oif} ${fwcmd} add deny all from 192.0.2.0/24 to any via ${oif} ${fwcmd} add deny all from 224.0.0.0/4 to any via ${oif} ${fwcmd} add deny all from 240.0.0.0/4 to any via ${oif}

# Allow established connections with minimal overhead ${fwcmd} add pass tcp from any to any established

# Allow IP fragments to pass through ${fwcmd} add pass all from any to any frag

### TCP RULES

# HTTP - Allow access to our web server ${fwcmd} add pass tcp from any to any 80 setup ${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 setup of any other TCP connection ${fwcmd} add pass tcp from any to any setup

### UDP RULES

# DNS - Allow queries out in the world ${fwcmd} add pass udp from any to ${dns1} 53 ${fwcmd} add pass udp from any to ${dns2} 53 ${fwcmd} add pass udp from ${dns1} 53 to any ${fwcmd} add pass udp from ${dns2} 53 to any

# SMB - Allow local traffic ${fwcmd} add pass udp from any to any 137-139 via ${iif}

# SYSLOG - Allow machines on inside net to log to us. ${fwcmd} add pass log udp from any to any 514 via ${iif}

# NTP - Allow 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 ${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 ${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 Header ${fwcmd} add pass icmp from any to any icmptypes 3,4,11,12 via ${oif}

# Deny the rest of them ${fwcmd} add deny log icmp from any to any

### MISCELLANEOUS REJECT RULES

# Reject broadcasts from outside interface ${fwcmd} add 63000 deny ip from any to 0.0.0.255:0.0.0.255 in via ${oif} # Allow broadcasts from inside interface ${fwcmd} add 63000 allow ip from any to 0.0.0.255:0.0.0.255 in via ${iif} ${fwcmd} add 63000 allow ip from any to 0.0.0.255:0.0.0.255 out via ${oif}

# Reject&Log SMB connections on outside interface ${fwcmd} add 64000 deny log udp from any to any 137-139 via ${oif}

# Reject&Log all other connections from outside interface ${fwcmd} add 65000 deny log ip from any to any via ${oif}

# Everything else is denied by default, unless the # IPFIREWALL_DEFAULT_TO_ACCEPT option is set in your kernel

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