I am trying to set up a basic firewall (as in very basic at the moment),
but I seem to be having some problems getting any web pages or doing dns
lookup's to the internet when i implement the firewall
I am using dialup on interface ppp0 to my isp (modem connection) and the
network is on eth0 (192.168.1.0/24),consisting of 2 machines
peer-peer,both have their own modem connection
I am trying to block any packets/requests to any internal interfaces
(apart from ones i send out) from ppp0.
Here are my rules so far (taking my isp_addy as 1.2.3.4,for security
sake):
# Flush out any exsisting rules
/sbin/ipchains -F
/sbin/ipchains -X
# Set default filters to deny everthing
/sbin/ipchains -P input DENY
/sbin/ipchains -P forward DENY
/sbin/ipchains -P output DENY
# Allow all internal loacalhost traffic
/sbin/ipchains -A input -i lo -j ACCEPT
/sbin/ipchains -A output -i lo -j ACCEPT
# Allow all internal network traffic
/sbin/ipchains -A input -i eth0 -j ACCEPT
/sbin/ipchains -A output -i eth0 -j ACCEPT
# --- TCP ---
/sbin/ipchains -A output -p tcp -j ACCEPT -i ppp0 -s 0.0.0.0/0 -d
1.2.3.4
/sbin/ipchains -A input -p tcp -j DENY -i ppp0 ! -y -s 1.2.3.4 -d
0.0.0.0/0
# --- UDP ---
/sbin/ipchains -A output -p udp -j ACCEPT -i ppp0 -s 0.0.0.0/0 -d
1.2.3.4
/sbin/ipchains -A input -p udp -j DENY -i ppp0 ! y -s 1.2.3.4 -d
0.0.0.0/0
from what i understand the '-s' is the source and '-d' is the
destination, so i assume that in the #--- TCP --- example,what i what to
do is:
allow any packets to go from anywhere on my network to the internet and
then DENY everything from the internet except headers that i sent
out,thus allowing me to browse the net,the same goes for UDP as well.
as its still not working,could anyone please point out where iam going
wrong.
Cheers
Mark
--
----
A penguin a day keeps the fatal exceptions away...
Registered Linux User: 208939
Licq: 119422259
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