paddy joesoap wrote:
Dear Experts
I am curious to know more about what FORWARD chain inbound and
outbound actually mean.
Example firewall set-up below:
Internet --- Firewall --- PC
Firewall has 2 interfaces: eth0 = External and eth1 = Internal
>From what I can gather from the Netfilter website, all I need to do is
create are inbound and outbound rules on the FORWARD chain.
To allow inbound Internet access, I specify:
FORWARD -i eth0
To allow outbound PC access, I specify:
FORWARD -o eth1
The question is from whose perspective do you view what is inbound and
what is outbound?
For example, in the case of the Internet client, traffic flowing
towards the firewall is indeed Inbound so naturally "FORWARD -i eth0"
is required. However, isn't it also Outbound on eth1, given that it
leaves interface eth1 to get to PC?
Similarly, clients on the internal network think of their traffic as
being outbound only, but when traffic is being "forwarded" from eth1
to eth0 heading for the Internet, isn't that traffic classed as
Inbound on eth0?
Do I need to create rules for this scenario also or is Netfilter
handling these implied situations?
Beginner questions so apologies in advance.
Paddy.
Please read this carefully and if you still have questions, ask them
afterwards:
http://www.frozentux.net/iptables-tutorial/iptables-tutorial.html#TRAVERSINGOFTABLES
http://jengelh.medozas.de/images/nf-packet-flow.png
but in short:
INPUT chain = packets destined to your host
OUTPUT chain = source of packets is your host
FORWARD chain = source is external - destination is external address
(forwarded, routed)
regards
Mart
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