For DHCP client configuration control the setting of the broadcast flag in the

DISCOVER message sent.

According to RFC2131:

   In the case of a client using DHCP for initial configuration (before
   the client's TCP/IP software has been completely configured), DHCP
   requires creative use of the client's TCP/IP software and liberal
   interpretation of RFC 1122.  The TCP/IP software SHOULD accept and
   forward to the IP layer any IP packets delivered to the client's
   hardware address before the IP address is configured; DHCP servers
   and BOOTP relay agents may not be able to deliver DHCP messages to
   clients that cannot accept hardware unicast datagrams before the
   TCP/IP software is configured.

   To work around some clients that cannot accept IP unicast datagrams
   before the TCP/IP software is configured as discussed in the previous
   paragraph, DHCP uses the 'flags' field [21].  The leftmost bit is
   defined as the BROADCAST (B) flag.  The semantics of this flag are
   discussed in section 4.1 of this document.  The remaining bits of the
   flags field are reserved for future use.  They MUST be set to zero by
   clients and ignored by servers and relay agents.  Figure 2 gives the
   format of the 'flags' field.

this changes means VPP conforms to the:
   "SHOULD accept and forward to the IP layer any IP packets delivered
    to the client's hardware address before the IP address is configured"
with the caveat that VPP allows DHCP packets destined to the stanard client
DHCP port to be delivered. With this enhancement the control-plane is now
able to choose the setting of the broadcast flag.

Change-Id: Ia4eb2c9bb1e30c29f9192facc645e9533641955a
Signed-off-by: Neale Ranns <nranns@cisco.com>

1 files changed, 53 insertions, 98 deletions

diff --git a/src/vnet/dhcp/client.c b/src/vnet/dhcp/client.c
index 8043bf22d43..03fc2689abf 100644
--- a/src/vnet/dhcp/client.c
+++ b/src/vnet/dhcp/client.c
@@ -22,56 +22,6 @@ static u8 *format_dhcp_client_state (u8 * s, va_list * va);
 static vlib_node_registration_t dhcp_client_process_node;
 
 static void
-dhcp_client_add_rx_address (dhcp_client_main_t * dcm, dhcp_client_t * c)
-{
-  /* Install a local entry for the offered address */
-  fib_prefix_t rx = {
-    .fp_len = 32,
-    .fp_addr.ip4 = c->leased_address,
-    .fp_proto = FIB_PROTOCOL_IP4,
-  };
-
-  fib_table_entry_special_add (fib_table_get_index_for_sw_if_index
-			       (FIB_PROTOCOL_IP4, c->sw_if_index), &rx,
-			       FIB_SOURCE_DHCP, (FIB_ENTRY_FLAG_LOCAL));
-
-  /* And add the server's address as uRPF exempt so we can accept
-   * local packets from it */
-  fib_prefix_t server = {
-    .fp_len = 32,
-    .fp_addr.ip4 = c->dhcp_server,
-    .fp_proto = FIB_PROTOCOL_IP4,
-  };
-
-  fib_table_entry_special_add (fib_table_get_index_for_sw_if_index
-			       (FIB_PROTOCOL_IP4, c->sw_if_index), &server,
-			       FIB_SOURCE_URPF_EXEMPT, (FIB_ENTRY_FLAG_DROP));
-}
-
-static void
-dhcp_client_remove_rx_address (dhcp_client_main_t * dcm, dhcp_client_t * c)
-{
-  fib_prefix_t rx = {
-    .fp_len = 32,
-    .fp_addr.ip4 = c->leased_address,
-    .fp_proto = FIB_PROTOCOL_IP4,
-  };
-
-  fib_table_entry_special_remove (fib_table_get_index_for_sw_if_index
-				  (FIB_PROTOCOL_IP4, c->sw_if_index), &rx,
-				  FIB_SOURCE_DHCP);
-  fib_prefix_t server = {
-    .fp_len = 32,
-    .fp_addr.ip4 = c->dhcp_server,
-    .fp_proto = FIB_PROTOCOL_IP4,
-  };
-
-  fib_table_entry_special_remove (fib_table_get_index_for_sw_if_index
-				  (FIB_PROTOCOL_IP4, c->sw_if_index), &server,
-				  FIB_SOURCE_URPF_EXEMPT);
-}
-
-static void
 dhcp_client_acquire_address (dhcp_client_main_t * dcm, dhcp_client_t * c)
 {
   /*
@@ -233,13 +183,6 @@ dhcp_client_for_us (u32 bi, vlib_buffer_t * b,
 	  c->next_transmit = now + 5.0;
 	  break;
 	}
-      /*
-       * in order to accept unicasted ACKs we need to configure the offered
-       * address on the interface. However, at this point we may not know the
-       * subnet-mask (an OFFER may not contain it). So add a temporary receice
-       * and uRPF excempt entry
-       */
-      dhcp_client_add_rx_address (dcm, c);
 
       /* Received an offer, go send a request */
       c->state = DHCP_REQUEST;
@@ -267,9 +210,11 @@ dhcp_client_for_us (u32 bi, vlib_buffer_t * b,
 	  void (*fp) (u32, u32, u8 *, u8, u8, u8 *, u8 *, u8 *) =
 	    c->event_callback;
 
-	  /* replace the temporary RX address with the correct subnet */
-	  dhcp_client_remove_rx_address (dcm, c);
+	  /* add the advertised subnet and disable the feature */
 	  dhcp_client_acquire_address (dcm, c);
+	  vnet_feature_enable_disable ("ip4-unicast",
+				       "ip4-dhcp-client-detect",
+				       c->sw_if_index, 0, 0, 0);
 
 	  /*
 	   * Configure default IP route:
@@ -285,8 +230,19 @@ dhcp_client_for_us (u32 bi, vlib_buffer_t * b,
 		.ip4 = c->router_address,
 	      };
 
-	      fib_table_entry_path_add (fib_table_get_index_for_sw_if_index (FIB_PROTOCOL_IP4, c->sw_if_index), &all_0s, FIB_SOURCE_DHCP, FIB_ENTRY_FLAG_NONE, DPO_PROTO_IP4, &nh, c->sw_if_index, ~0, 1, NULL,	// no label stack
-					FIB_ROUTE_PATH_FLAG_NONE);
+              /* *INDENT-OFF* */
+	      fib_table_entry_path_add (
+                  fib_table_get_index_for_sw_if_index (
+                      FIB_PROTOCOL_IP4,
+                      c->sw_if_index),
+                  &all_0s,
+                  FIB_SOURCE_DHCP,
+                  FIB_ENTRY_FLAG_NONE,
+                  DPO_PROTO_IP4,
+                  &nh, c->sw_if_index,
+                  ~0, 1, NULL,	// no label stack
+                  FIB_ROUTE_PATH_FLAG_NONE);
+              /* *INDENT-ON* */
 	    }
 
 	  /*
@@ -418,7 +374,9 @@ send_dhcp_pkt (dhcp_client_main_t * dcm, dhcp_client_t * c,
   dhcp->hardware_type = 1;	/* ethernet */
   dhcp->hardware_address_length = 6;
   dhcp->transaction_identifier = c->transaction_id;
-  dhcp->flags = clib_host_to_net_u16 (is_broadcast ? DHCP_FLAG_BROADCAST : 0);
+  dhcp->flags =
+    clib_host_to_net_u16 (is_broadcast && c->set_broadcast_flag ?
+			  DHCP_FLAG_BROADCAST : 0);
   dhcp->magic_cookie.as_u32 = DHCP_MAGIC;
 
   o = (dhcp_option_t *) dhcp->options;
@@ -676,14 +634,13 @@ dhcp_client_process (vlib_main_t * vm,
 	  break;
 
 	case ~0:
-	  pool_foreach (c, dcm->clients, (
-					   {
-					   timeout =
-					   dhcp_client_sm (now, timeout,
-							   (uword) (c -
-								    dcm->clients));
-					   }
-			));
+          /* *INDENT-OFF* */
+	  pool_foreach (c, dcm->clients,
+          ({
+            timeout = dhcp_client_sm (now, timeout,
+                                      (uword) (c - dcm->clients));
+          }));
+          /* *INDENT-ON* */
 	  if (pool_elts (dcm->clients) == 0)
 	    timeout = 100.0;
 	  break;
@@ -785,13 +742,14 @@ show_dhcp_client_command_fn (vlib_main_t * vm,
       return 0;
     }
 
-  pool_foreach (c, dcm->clients, (
-				   {
-				   vlib_cli_output (vm, "%U",
-						    format_dhcp_client, dcm,
-						    c, verbose);
-				   }
-		));
+  /* *INDENT-OFF* */
+  pool_foreach (c, dcm->clients,
+  ({
+    vlib_cli_output (vm, "%U",
+                     format_dhcp_client, dcm,
+                     c, verbose);
+  }));
+  /* *INDENT-ON* */
 
   return 0;
 }
@@ -812,11 +770,6 @@ dhcp_client_add_del (dhcp_client_add_del_args_t * a)
   vlib_main_t *vm = dcm->vlib_main;
   dhcp_client_t *c;
   uword *p;
-  fib_prefix_t all_1s = {
-    .fp_len = 32,
-    .fp_addr.ip4.as_u32 = 0xffffffff,
-    .fp_proto = FIB_PROTOCOL_IP4,
-  };
   fib_prefix_t all_0s = {
     .fp_len = 0,
     .fp_addr.ip4.as_u32 = 0x0,
@@ -840,6 +793,7 @@ dhcp_client_add_del (dhcp_client_add_del_args_t * a)
       c->option_55_data = a->option_55_data;
       c->hostname = a->hostname;
       c->client_identifier = a->client_identifier;
+      c->set_broadcast_flag = a->set_broadcast_flag;
       do
 	{
 	  c->transaction_id = random_u32 (&dcm->seed);
@@ -848,17 +802,18 @@ dhcp_client_add_del (dhcp_client_add_del_args_t * a)
       set_l2_rewrite (dcm, c);
       hash_set (dcm->client_by_sw_if_index, a->sw_if_index, c - dcm->clients);
 
-      /* this add is ref counted by FIB so we can add for each itf */
-      fib_table_entry_special_add (fib_table_get_index_for_sw_if_index
-				   (FIB_PROTOCOL_IP4, c->sw_if_index),
-				   &all_1s, FIB_SOURCE_DHCP,
-				   FIB_ENTRY_FLAG_LOCAL);
-
       /*
-       * enable the interface to RX IPv4 packets
-       * this is also ref counted
+       * In order to accept any OFFER, whether broadcasted or unicasted, we
+       * need to configure the dhcp-client-detect feature as an input feature
+       * so the DHCP OFFER is sent to the ip4-local node. Without this a
+       * broadcasted OFFER hits the 255.255.255.255/32 address and a unicast
+       * hits 0.0.0.0/0 both of which default to drop and the latter may forward
+       * of box - not what we want. Nor to we want to change these route for
+       * all interfaces in this table
        */
-      ip4_sw_interface_enable_disable (c->sw_if_index, 1);
+      vnet_feature_enable_disable ("ip4-unicast",
+				   "ip4-dhcp-client-detect",
+				   c->sw_if_index, 1, 0, 0);
 
       vlib_process_signal_event (vm, dhcp_client_process_node.index,
 				 EVENT_DHCP_CLIENT_WAKEUP, c - dcm->clients);
@@ -867,10 +822,6 @@ dhcp_client_add_del (dhcp_client_add_del_args_t * a)
     {
       c = pool_elt_at_index (dcm->clients, p[0]);
 
-      fib_table_entry_special_remove (fib_table_get_index_for_sw_if_index
-				      (FIB_PROTOCOL_IP4, c->sw_if_index),
-				      &all_1s, FIB_SOURCE_DHCP);
-
       if (c->router_address.as_u32)
 	{
 	  ip46_address_t nh = {
@@ -883,9 +834,7 @@ dhcp_client_add_del (dhcp_client_add_del_args_t * a)
 				       DPO_PROTO_IP4, &nh, c->sw_if_index, ~0,
 				       1, FIB_ROUTE_PATH_FLAG_NONE);
 	}
-      dhcp_client_remove_rx_address (dcm, c);
       dhcp_client_release_address (dcm, c);
-      ip4_sw_interface_enable_disable (c->sw_if_index, 0);
 
       vec_free (c->option_55_data);
       vec_free (c->hostname);
@@ -903,7 +852,8 @@ dhcp_client_config (vlib_main_t * vm,
 		    u8 * hostname,
 		    u8 * client_id,
 		    u32 is_add,
-		    u32 client_index, void *event_callback, u32 pid)
+		    u32 client_index,
+		    void *event_callback, u8 set_broadcast_flag, u32 pid)
 {
   dhcp_client_add_del_args_t _a, *a = &_a;
   int rv;
@@ -914,6 +864,7 @@ dhcp_client_config (vlib_main_t * vm,
   a->client_index = client_index;
   a->pid = pid;
   a->event_callback = event_callback;
+  a->set_broadcast_flag = set_broadcast_flag;
   vec_validate (a->hostname, strlen ((char *) hostname) - 1);
   strncpy ((char *) a->hostname, (char *) hostname, vec_len (a->hostname));
   vec_validate (a->client_identifier, strlen ((char *) client_id) - 1);
@@ -990,6 +941,7 @@ dhcp_client_set_command_fn (vlib_main_t * vm,
   u32 sw_if_index;
   u8 *hostname = 0;
   u8 sw_if_index_set = 0;
+  u8 set_broadcast_flag = 1;
   int is_add = 1;
   dhcp_client_add_del_args_t _a, *a = &_a;
   int rv;
@@ -1003,6 +955,8 @@ dhcp_client_set_command_fn (vlib_main_t * vm,
 	;
       else if (unformat (input, "del"))
 	is_add = 0;
+      else if (unformat (input, "broadcast", &set_broadcast_flag))
+	is_add = 0;
       else
 	break;
     }
@@ -1015,6 +969,7 @@ dhcp_client_set_command_fn (vlib_main_t * vm,
   a->sw_if_index = sw_if_index;
   a->hostname = hostname;
   a->client_identifier = format (0, "vpe 1.0%c", 0);
+  a->set_broadcast_flag = set_broadcast_flag;
 
   /*
    * Option 55 request list. These data precisely match