Enable Loopback confuse
rob0 at gmx.co.uk
Fri Aug 19 15:18:26 CEST 2005
On Friday 2005-August-19 05:41, nattapon viroonsri wrote:
> When i enable loopback i just use 2 line below and everything work
> fine iptables -A INPUT -i lo -j ACCEPT
> iptables -A OUTPUT -o lo -j ACCEPT
Correct, unless earlier rules do something to prevent these rules from
> But i see many example around then have also included this line
> below to enable loopback
> iptables -A FORWARD -o lo - j ACCEPT ?
They are wrong. FORWARD rules are checked when *both* the source and
destination IP's are not local. Normal loopback traffic can never hit
the FORWARD chain.
> So can i omit this line ?
> or what kind of packet that match this rule ?
Yes. None. It's possibly true that specially-crafted packets and silly
routing could be employed, but this is not a real-world situation.
filter table IP address
built-in chains source destination
---------------- ------ -----------
INPUT n/a local
OUTPUT local not local
FORWARD not local not local
Each packet is checked against the rules in only one of the built-in
chains, *except* loopback traffic, which hits OUTPUT going out, and
then INPUT coming in.
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