Re: [lwip-users] Changing Port number at run time

[Sanchayan]

Hello,

The use case is as follows.

Assume that your product uses lwip for communicating over TCP IP. Now, 
you want to access this particular device, from a remote location. Lets 
say you are in one part of the country, where in a particular LAN, this 
device is being used. One way of accessing this device from a remote 
location, would be to have the device get a static IP assigned. But, 
let's say there are N number of devices, it's not possible to assign 
each of them a static IP, as these would require a fixed annual charge 
from the ISP for each IP being used.

Now, consider a scenario where port number can be changed at run time. I 
assign each device a particular local IP, and each device is assigned a 
port number, which the customer wants. This port number has to be 
configurable. So, all these devices are now connected to a router. In 
the router configuration settings, the port number for each device is 
forwarded. For device x, say 2101 is forwarded and for device y, sat 
2102 is forwarded. The router will be given a static IP. Now, assuming, 
let's say the router static IP address is 10.17.3.96 you would be able 
to access the device x with 10.17.3.96/2101 and device y with 
10.17.3.96/2102.

I wasn't aware lwiplib.c file was a part of the Stellaris port and not 
lwip. You are right Simon Goldschmidt.

I managed to change the port number, by doing this.

1. Send a command for changing the port number.
2. Then run the below code.

tcp_close(pcb);             //Close the pcb being used currently

pcb = tcp_new();         // Create a new pcb

tcp_bind( pcb, IP_ADDR_ANY, port_number );    // Bind the pcb to the new 
port number received from command

pcb = tcp_listen( pcb ); // Put the pcb in listen state

tcp_accept( pcb, connection_accept );             // Define the function 
for accepting connections

Now, this works. I can now connect to the device over the new port 
number. But, i can also connect to the device over the old port number, 
which was being used. Can this be prevented in some way. In my scenario, 
i guess i will not face any problems, as the router will take care of 
this, by binding the IP of the device to the port number and i won't get 
requests over the old port number, but, is there a way of preventing it?

Or should i do a system reset which will initialize my lwip stack anew 
with the new port number. The port number will be written to flash non 
volatile memory.


--
Thanks & Regards,
Sanchayan Maity.




On 03-10-2012 15:14, junix wrote:
> Quoting Simon Goldschmidt <address@hidden>:
>
> > Sanchayan wrote:
> > > I tried to see in lwiplib.c file, if there is a function like 
> > > lwIPNetworkConfigChange(), which will help me change the port number 
> > > for a particular connection.
> > I don't know that file, which suggests it is not part of lwIP itself 
> > but rather part of a specific lwIP port.
> You are right. It's part of the Stellaris-Port that TI did. According 
> to the documentation, the function he mentioned uses either 
> netif_set_addr or does the DHCP stuff needed to get/change the IP-Adress:
> > //! This function will evaluate the new configuration data.  If 
> > necessary, the
> > //! interface will be brought down, reconfigured, and then brought 
> > back up
> > //! with the new configuration.
>
> > > I have got a connection running in listening mode on a particular 
> > > port. For giving Dynamic DNS provision, i need to change the port 
> > > number of my listening connection at run time.
> I don't understand this one. What exactly do you want to achieve? I 
> don't yet get why you need to change the port number of your LISTENING 
> port at runtime?
>
> Regards
> Ueli
>
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> lwip-users mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/lwip-users




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