Question about /etc/iptables.down.rules

Question about /etc/iptables.down.rules

[TinyApps.Org]

I have a very simple set of iptables rules:

# iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
# iptables -A INPUT -p tcp -i eth0 --dport ssh -j ACCEPT
# iptables -I INPUT -i lo -j ACCEPT
# iptables -A INPUT -j DROP

which has been saved to /etc/iptables.up.rules .

I have also modified /etc/network/interfaces to use the ruleset:

            iface eth0 inet static
                    address x.x.x.x
                    [.. interface configuration ..]
                    pre-up iptables-restore < /etc/iptables.up.rules

I understand that it is best to setup a set of rules to be applied
when the network interface is down, saving it to:

  /etc/iptables.down.rules

and applying in /etc/network/interfaces via:

post-down iptables-restore < /etc/iptables.down.rules

What should this set of rules look like? The exact opposite
of /etc/iptables.up.rules ? Or just a simple flush command?
Or something else altogether?

Sincerely,

Miles

Re: Question about /etc/iptables.down.rules

[Покотиленко Костик]

В Вск, 26/08/2007 в 15:51 -1000, TinyApps.Org пишет:
> I have a very simple set of iptables rules:
> 
> # iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
> # iptables -A INPUT -p tcp -i eth0 --dport ssh -j ACCEPT
> # iptables -I INPUT -i lo -j ACCEPT
> # iptables -A INPUT -j DROP
> 
> which has been saved to /etc/iptables.up.rules .
> 
> I have also modified /etc/network/interfaces to use the ruleset:
> 
>             iface eth0 inet static
>                     address x.x.x.x
>                     [.. interface configuration ..]
>                     pre-up iptables-restore < /etc/iptables.up.rules
> 
> I understand that it is best to setup a set of rules to be applied
> when the network interface is down, saving it to:
> 
>   /etc/iptables.down.rules
> 
> and applying in /etc/network/interfaces via:
> 
> post-down iptables-restore < /etc/iptables.down.rules
> 
> What should this set of rules look like? The exact opposite
> of /etc/iptables.up.rules ? Or just a simple flush command?
> Or something else altogether?

You can do a simple flush, but this is not required, since all rules
will be overwritten by iptables-restore when you bring network interface
up next time.

-- 
Покотиленко Костик <casper@meteor.dp.ua>

Re: Question about /etc/iptables.down.rules

[TinyApps.Org]

Thanks for your reply, Покотиленко! (I hope that is the correct name  
to use.)
My reply is at the bottom of this message:

>> I understand that it is best to setup a set of rules to be applied
>> when the network interface is down, saving it to:
>>
>>   /etc/iptables.down.rules
>>
>> and applying in /etc/network/interfaces via:
>>
>> post-down iptables-restore < /etc/iptables.down.rules
>>
>> What should this set of rules look like? The exact opposite
>> of /etc/iptables.up.rules ? Or just a simple flush command?
>> Or something else altogether?
>
> You can do a simple flush, but this is not required, since all rules
> will be overwritten by iptables-restore when you bring network  
> interface
> up next time.

I had stumbled across the following comment:

"But to do this really clean, we need to have a script that removes  
the rules as well for when the interface goes down. Just to make sure  
the rules are never added twice."

on this site:
http://my.opera.com/Jada0007/blog/show.dml/1213354

and therefore wondered if there were ever a case in which
the rules could be applied twice... by creating a /etc/ 
iptables.down.rules
file, I hoped to avoid such a possibility.

Sincerely,

Miles

Re: Question about /etc/iptables.down.rules

[Покотиленко Костик]

В Вск, 26/08/2007 в 22:01 -1000, TinyApps.Org пишет:
> Thanks for your reply, Покотиленко! (I hope that is the correct name  
> to use.)
> My reply is at the bottom of this message:
> 
> >> I understand that it is best to setup a set of rules to be applied
> >> when the network interface is down, saving it to:
> >>
> >>   /etc/iptables.down.rules
> >>
> >> and applying in /etc/network/interfaces via:
> >>
> >> post-down iptables-restore < /etc/iptables.down.rules
> >>
> >> What should this set of rules look like? The exact opposite
> >> of /etc/iptables.up.rules ? Or just a simple flush command?
> >> Or something else altogether?
> >
> > You can do a simple flush, but this is not required, since all rules
> > will be overwritten by iptables-restore when you bring network  
> > interface
> > up next time.
> 
> I had stumbled across the following comment:
> 
> "But to do this really clean, we need to have a script that removes  
> the rules as well for when the interface goes down. Just to make sure  
> the rules are never added twice."
> 
> on this site:
> http://my.opera.com/Jada0007/blog/show.dml/1213354
> 
> and therefore wondered if there were ever a case in which
> the rules could be applied twice... by creating a /etc/ 
> iptables.down.rules
> file, I hoped to avoid such a possibility.

man iptables-restore states:
...
       -n, --noflush

       don't flush the previous contents of the table. If not specified,
              iptables-restore flushes (deletes) all previous contents
of  the
              respective IP Table.
...

So, make sure you won't use "-n" option when calling iptables-restore.

-- 
Покотиленко Костик <casper@meteor.dp.ua>