[lwip-users] How to securely switch between DHCP and static IP assignment?

[Benjamin Schelte]

Hallo all,

 

I am having trouble to securely switch between DHCP and static IP assignment. The way I am doing this at the moment is sometimes leading to an assert (please read further).

So far I am quite satisfied with the lwip-stack and its performance, but this problem gives me a headache.

 

Description:

My environment needs to be able to switch between static IP and DHCP during runtime. This should be possible at any point in time (although once configured it will most likely stay the same…).

Info: I am using a Realtime OS.

 

So after initialization either with DHCP or static IP address assignment I use two functions to switch between those 2 modes.

Both functions are called out of a user menu. The code looks like the following:

 

 

int iEthCtrl_UseStaticIP(unsigned long ulIPAddress, unsigned long ulIPGateway, unsigned long ulIPSubnetMask)

{

      struct ip_addr xIpAddr, xNetMask, xGateway;

 

      // Check, if the network connection is up and DHCP is activated

      if ((sNetif.flags & NETIF_FLAG_UP) && (sNetif.flags & NETIF_FLAG_DHCP)) {

            // Release the DHCP lease (it already calls netif_set_down() function)

            dhcp_release(&sNetif);

 

            // Stop the dhcp service

            dhcp_stop(&sNetif);

 

            xIpAddr.addr = ulIPAddress;

            xGateway.addr = ulIPGateway;

            xNetMask.addr = ulIPSubnetMask;

 

            // Set the new ip address

            netif_set_addr(&sNetif, &xIpAddr, &xNetMask, &xGateway);

 

            // Bring the interface up again

            netif_set_up(&sNetif);

 

      }

...

}

 

int iEthCtrl_UseDHCP(void)

{

      struct ip_addr xIpAddr, xNetMask, xGateway;

 

      IP4_ADDR(&xIpAddr, 0, 0, 0, 0);

      IP4_ADDR(&xNetMask, 0, 0, 0, 0);

      IP4_ADDR(&xGateway, 0, 0, 0, 0);

 

      // Check, if the network connection is up and DHCP is NOT activated

      if ((sNetif.flags & NETIF_FLAG_UP) && !(sNetif.flags & NETIF_FLAG_DHCP)) {

            // Bring the current interface down

            netif_set_down(&sNetif);

 

            // Set the IP addresses to "0.0.0.0" so the DHCP server can send a reply.

            // Otherwise the previous static IP might be out of the network class of the DHCP server

            netif_set_addr(&sNetif, &xIpAddr, &xNetMask, &xGateway);

 

            // Start DHCP negotiation

            if (sNetif.dhcp == NULL) {

                  dhcp_start(&sNetif);

            }

            else {

                  dhcp_network_changed(&sNetif);

            }

...

      }

...

}

 

 

Furthermore I am using a callback function to read the (cable) link status from the PHY every 500ms:

 

static void vPrvEthCtrl_CheckLinkStatusCallback(void* pvParams)

{

      volatile avr32_macb_t *macb = &AVR32_MACB;

      unsigned long ulStatusReg;

 

      ulStatusReg = ulReadMDIO(macb, PHY_BMSR);      // Can be blocking!

      if (ulStatusReg & BMSR_LSTATUS) {

            // If the cable was disconnected previously we set the link up again

            if (bLinkStatus == FALSE) {

                  netif_set_link_up(&sNetif);

            }

            bLinkStatus = TRUE;

      }

      else {

            if (bLinkStatus == TRUE) {

                  netif_set_link_down(&sNetif);

                  netif_set_down(&sNetif);

            }

            bLinkStatus = FALSE;

      }

}

 

So the problem occurs after calling the function iEthCtrl_UseDHCP().

After doing so it sometimes happens to stop executing on an assert in dhcp_create_request().

Assert:

LWIP_ASSERT("dhcp_create_request: dhcp->p_out == NULL", dhcp->p_out == NULL);

 

Callstack:

dhcp_create_request

dhcp_select

dhcp_handle_offer

dhcp_recv

udp_input

ip_input

ethernet_input

tcpip_thread

 

 

So my questions are the following.

Why is a DHCP-request forwarded to the DHCP-handler, although dhcp_stop() has been called before?

Is the way I switch from static IP to DHCP and vice versa correct?

Any comment or advice is appreciated.

 

Thanks in advance!

 

Best regards,

Benjamin Schelte