Re: passive mode ftp high ports driving me nuts

[MargoAndTodd <margoandtodd@gmail.com>]

On 01/09/2010 06:04 AM, Mart Frauenlob wrote:
> On 09.01.2010 14:55, Mart Frauenlob wrote:
>> On 09.01.2010 03:59, MargoAndTodd wrote:
>>> On 01/08/2010 02:24 AM, Mart Frauenlob wrote:
>>>
>>>>> It is the "--sport $unassgn --dport $unassgn" that is killing me.
>>>>> How do I restrict the last three to just passive mode ftp?
>>>>>
>>>>
>>>> use the 'helper' match extension. i.e: -m helper --helper ftp.
>>>> if you need to distinguish between active and passive, you still can use
>>>> the port and state matches for that.
>>>
>>> Hi Mart,
>>>
>>> Works perfectly.  Thank you!
>>>
>>> -T
>>>
>>> p.s. my new rules:
>>>
>
> [...]
>
>>
>> if you use user-defined chains (which is good), take full advantage of
>> it, by not repeating so many values in your ruleset. i.e. dsl-in will
>> always have -i eth1 and -d $eth1_addr.
>> you don't need -d $ANY_IP, just leave it out, gives the same result.
>> you don't need --syn, if you rely on conntrack helper match.
>>
>> let me suggest a more structured approach:
>>
>
> [...]
>
>>
>> as an untested example with some additional design considerations for
>> invalid packets and related icmp.
>>
>
> sorry had the naming for dsl-for and dsl-fwd mixed up, again corrected:
>
> # assuming DROP policy for INPUT,OUTPUT,FORWARD...
>
>
> for x in dsl-in dsl-out dsl-for invalid; do
> 	$ipt -N $x
> done
>
> # sort out the illegal packets - could add more eventually...
> $ipt -A invalid -p tcp ! --syn -m state --state NEW -j DROP
> $ipt -A invalid -m state --state INVALID -j DROP
>
> # global rules:
> # allow established - speed up processing by placing rule on top
> # then sort out bad ones
> # allow related icmp
> for x in INPUT OUTPUT FORWARD; do
> 	$ipt -A $x -m state ESTABLISHED -j ACCEPT
> 	$ipt -A $x -j invalid
> 	$ipt -A $x -p icmp -m state --state RELATED -j ACCEPT
> done
>
> # allow the related ftp packets
> for x in dsl-in dsl-out dsl-for; do
> 	$ipt -A $x -m helper --helper ftp -j ACCEPT
> done
>
> # allow new outgoing ftp connections
> $ipt -A dsl-out -p tcp --dport 21 -m state --state NEW -j ACCEPT
> $ipt -A dsl-for -s $internal_net -p tcp --dport 21 -m state --state NEW
> -j ACCEPT
>
> # jump tree
> $ipt -A INPUT -i eth1 -d $eth1_addr -j dsl-in
> $ipt -A OUTPUT -o eth1 -s $eth1_addr -j dsl-out
> $ipt -A FORWARD -i eth1 -d $internal_net -j dsl-for
> $ipt -A FORWARD -o eth1 -s $internal_net -j dsl-for
>


Thank you!