udhcpd initial lease

[Grahame Jordan]

Hi,

When using dhcpd on an embedded system after booting on some clients for 
example Windows7 it takes a long time
to negotiate an ip address. In the case of Win7 it is insistent on using 
the previous IP address that it had at its previous
connection to the device.

The problem is that on most embedded systems the leases file is empty 
after every boot. Making the negotiation
difficult as there is no previous record in the leases file to negotiate 
with. The lease request needs to time out before
a new lease can be requested resulting in long delays on getting an IP 
Address.
Additionally some embedded systems generate a random MAC address every 
time they connect say over USB making the
negotiation just as difficult as with an empty leases file.

I have created a patch that allows a request to go through if the leases 
file is empty. This results in very quick dhcp
negotiating. To alleviate the random MAC address issue I empty the 
leases file which results in quick dhcp negotiation also.

In this case only one client ever connects to these types of device. The 
requested IP address is then parsed later in the code to ensure that it 
is in the correct range etc.

  --- busybox-1.13.2/networking/udhcp/dhcpd.c    2010-11-17 
09:08:17.870655217 +1100
+++ busybox-1.13.2-new/networking/udhcp/dhcpd.c    2010-11-17 
09:22:22.600650751 +1100
@@ -229,12 +229,14 @@
                      /* make some contention for this address */
                      } else
                          send_NAK(&packet);
-                } else {
-                    uint32_t r = ntohl(requested_align);
-                    if (r < server_config.start_ip
-                         || r > server_config.end_ip
-                    ) {
-                        send_NAK(&packet);
+                } else { /* Lets see if the leases file is empty. If so 
why not add 'requested' address */
+                    if (is_initial_lease() && send_offer(&packet) < 0) {
+                        uint32_t r = ntohl(requested_align);
+                        if (r < server_config.start_ip
+                             || r > server_config.end_ip
+                        ) {
+                            send_NAK(&packet);
+                        }
                      }
                      /* else remain silent */
                  }
--- busybox-1.13.2/networking/udhcp/dhcpd.h    2010-11-17 
09:08:17.870655217 +1100
+++ busybox-1.13.2-new/networking/udhcp/dhcpd.h    2010-11-17 
09:08:17.870655217 +1100
@@ -84,6 +84,7 @@

  struct dhcpOfferedAddr *add_lease(const uint8_t *chaddr, uint32_t 
yiaddr, unsigned long lease) FAST_FUNC;
  int lease_expired(struct dhcpOfferedAddr *lease) FAST_FUNC;
+int is_initial_lease(void) FAST_FUNC;
  struct dhcpOfferedAddr *find_lease_by_chaddr(const uint8_t *chaddr) 
FAST_FUNC;
  struct dhcpOfferedAddr *find_lease_by_yiaddr(uint32_t yiaddr) FAST_FUNC;
  uint32_t find_address(int check_expired) FAST_FUNC;
--- busybox-1.13.2/networking/udhcp/leases.c    2010-11-17 
09:08:17.882035995 +1100
+++ busybox-1.13.2-new/networking/udhcp/leases.c    2010-11-17 
09:08:17.870655217 +1100
@@ -69,6 +69,15 @@
  }


+/* Is this the initial lease. ie. Is the leases file empty? */
+int FAST_FUNC is_initial_lease(void)
+{
+    if(leases[0].yiaddr == 0)
+        return 1;
+    return 0;
+}
+
+
  /* Find the first lease that matches chaddr, NULL if no match */
  struct dhcpOfferedAddr* FAST_FUNC find_lease_by_chaddr(const uint8_t 
*chaddr)
  {

Thanks

Grahame Jordan