Re: question about table filter, nat and mangle with chain default policy

[Mart Frauenlob <mart.frauenlob@chello.at>]

my mail wrote:
> I have rule like this
>
> ----- rule iptables -----
> # Remove any existing rules from all chains
> $IPT --flush
> $IPT -t nat --flush
> $IPT -t mangle --flush
> # Delete any user defined chains
> $IPT -X
> $IPT -t nat -X
> $IPT -t mangle -X
> # Reset default policy to ACCEPT
> $IPT --policy INPUT ACCEPT
> $IPT --policy OUTPUT ACCEPT
> $IPT --policy FORWARD ACCEPT
> $IPT -t nat --policy PREROUTING ACCEPT
> $IPT -t nat --policy OUTPUT ACCEPT
> $IPT -t nat --policy POSTROUTING ACCEPT
> $IPT -t mangle --policy PREROUTING ACCEPT
> $IPT -t mangle --policy INPUT ACCEPT
> $IPT -t mangle --policy FORWARD ACCEPT
> $IPT -t mangle --policy OUTPUT ACCEPT
> $IPT -t mangle --policy POSTROUTING ACCEPT
>
> # Unlimited traffic on the loopback interface
> $IPT -A INPUT -i lo -j ACCEPT
> $IPT -A OUTPUT -o lo -j ACCEPT
>
> # Default policy to DROP
> $IPT --policy INPUT DROP
> $IPT --policy OUTPUT DROP
> $IPT --policy FORWARD DROP
> #$IPT -t nat --policy PREROUTING DROP
> $IPT -t nat --policy OUTPUT DROP
> #$IPT -t nat --policy POSTROUTING DROP
> #$IPT -t mangle --policy PREROUTING DROP
> #$IPT -t mangle --policy INPUT DROP
> #$IPT -t mangle --policy FORWARD DROP
> #$IPT -t mangle --policy OUTPUT DROP
> #$IPT -t mangle --policy POSTROUTING DROP
>
> # For SSH Connection into Firewall
> $IPT -A INPUT -i $LAN_IF -p tcp --sport $SSH_PORTS -d $IPADDR --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
> $IPT -A OUTPUT -o $LAN_IF -p tcp ! --syn -s $IPADDR --sport 22 --dport $SSH_PORTS -m state --state ESTABLISHED -j ACCEPT
>
> ---------- end rule --------------
>
> this rule ok, because i can ssh-ing into this machine. But if i remove the # from default policy like this
>
> # Default policy to DROP
> $IPT --policy INPUT DROP
> $IPT --policy OUTPUT DROP
> $IPT --policy FORWARD DROP
> $IPT -t nat --policy PREROUTING DROP
> $IPT -t nat --policy OUTPUT DROP
> $IPT -t nat --policy POSTROUTING DROP
> $IPT -t mangle --policy PREROUTING DROP
> $IPT -t mangle --policy INPUT DROP
> $IPT -t mangle --policy FORWARD DROP
> $IPT -t mangle --policy OUTPUT DROP
> $IPT -t mangle --policy POSTROUTING DROP
>
> i can't ssh-ing into this machine. so is the ssh using nat and mangle table to connect into this machine?
> i litle bit confuse about this, why i can ssh-ing into this machine when i drop the nat and mangle table.
>
> thx in advance for your help
>   
Don't set the policy to DROP in mangle and nat table.
Put the drop policy only in filter table.

greets

Mart