Re: POP3 (Port No. 110)

[Georgi Alexandrov <tehlists@hotpop.com>]

Taylor, Grant wrote:

>> I have Sendmail configured on my server and I am able to send and
>> receive mails in the intranet. Now I want to be able to access the
>> mails from outside world also but i dont want to open the port for
>> every one. I want to open the pop3 port for the perticular IP (it may
>> be static or dynamic IP) in the IPTABLES and close the port when not
>> needed to access from outside.
>>
>> Please some one tell me how to do this and can I have some script
>> which will open the port when i need and close when not needed so that
>> I don't have to enter into the iptables every time.
>>
>> How to open the pop3 port for a perticular external ipaddress
>
>
> Presuming that you are not filtering on output it is easy to allow a 
> specific IP access to your POP3 server.
>
> iptables -t filter -A INPUT -s ! ${known_external_ip_address} -p tcp 
> --dport 110 -j DROP
>
> This will drop any traffic that comes to port 110 that is not from the 
> known external ip address.
>
> If you are wanting more help setting up a script to manage this for 
> you such that you can say pop_open and / or pop_close let me know and 
> I'll see what I can whip up.
>
>
>
> Grant. . . .
>
>
I think he is talking about port knocker.

"iptables -t filter -A INPUT -s ! ${known_external_ip_address} -p tcp 
--dport 110 -j DROP "
that rule is heavily dependant on his chain policies. E.g. if he has 
DROP policy on the INPUT chain (-t filter) that rule won't help much as 
${known_external_ip_address} will continue traversing the rules until it 
hits the DROP policy.

georgi ...

georgi