[Discuss] Limit the number of ip addresses which can connect to a port

[Tom Luo]

Hi, Derek,

Thanks for your suggestions. However, this is not exactly what I want.
The service is running in the server. Users can only connect to the server
using an assigned TCP port and a password.
This service using port/password to identify a user. Different users will
get different ports and their own unique password.
For example, user A will connect to port 8001 using password "testpassword".
User B will connect to port 8002 using password "testpassword2".
Every user has to pay a fee to use the service.
This works very well if no user shares port/password with other people.
To reduce this passowrd/port sharing issue, I propose to limit the number
of ip addresses connected to a port.
If a user A (assigned port 8010) shares his/her password with a person C,
user A can connect to port 8010 and use the service.
If at the same time the person C tries to connect to port 8010 from another
ip address. the firewall should decline the new connection.
I also check the connections and I see one user can have many connections
to the assigned port at the same time. So, I cannot use the number of
active connections on a port to solve this issue.
The only thing I can think about is using IP address. I think video service
providers like hulu and netflix face the same issue. But, I don't know how
they deal with the password sharing issue.

I hope I explained the issue clearly. BTW, I don't have the source code of
the service, so I cannot change the service itself.

Thanks a lot!

Tom


On Wed, Nov 1, 2017 at 10:54 AM, Derek Atkins <warlord at mit.edu> wrote:

> Tom,
>
> Tom Luo <mariolzx at gmail.com> writes:
>
> > Yes. I want only one IP gets access to the service. However, I don't own
> > this application and I don't have the source code. That is why I can only
> > using firewall to handle it.
> > If there is no software capable to handle this, I am thinking about
> writing
> > a shell script to do it myself.
>
> Just so I understand:   You have a service running on a server which
> *anyone* can use.  But once *someone* is using it, further connections
> can only come from that single IP address.   And then, once all
> connections drop again (i.e., nobody is using the service), then it
> opens up to anyone on any IP address again until someone else connects?
>
> Do I have this right?
>
> If so, I'm honestly not sure how to do this outside the application
> itself.  You MIGHT be able to do it with tcp_wrappers with some state on
> the machine for the number of open connections.
>
> Another option is that you MIGHT be able to do this with something like
> fail2ban + firewalld.  Every time there is a first-time connection then
> you add a firewall rule that limits access to only that IP address, and
> then once the user "logs out" you remove that restriction.  Of course
> you would need to ensure that the connection/disconnection get logged
> properly, and you'd need to write the fail2ban scripts.
>
> If you cannot modify the application itself then this might be
> challenging to get all the connect/disconnect messages to properly line
> up.
>
> > Thanks,
>
> -derek
>
> --
>        Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
>        Member, MIT Student Information Processing Board  (SIPB)
>        URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
>        warlord at MIT.EDU                        PGP key available
>