DHCP Client: receive unicast ACKs
despite VPP DHCP client setting neither ciaddr nor giaddr and setting the broadcast bit (see RFC 2131 section 4.1) some DHCP servers will still send a unicast DCHPACK. So as not to drop this VPP must have both 1) a receive FIB entry for the OFFERED IP adress and 2) a 'don't drop me because of uRPF' FIB entry for the DHCP server's address.
Change-Id: I167d858deb45629318cbdccf5bf67d971730a42f
Signed-off-by: Neale Ranns <nranns@cisco.com>
diff --git a/src/vnet/dhcp/client.c b/src/vnet/dhcp/client.c
index 25ab317..cfe62a6 100644
--- a/src/vnet/dhcp/client.c
+++ b/src/vnet/dhcp/client.c
@@ -22,6 +22,70 @@
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)
{
/*
@@ -95,7 +159,9 @@
/* parse through the packet, learn what we can */
if (dhcp->your_ip_address.as_u32)
c->leased_address.as_u32 = dhcp->your_ip_address.as_u32;
-
+
+ c->dhcp_server.as_u32 = dhcp->server_ip_address.as_u32;
+
o = (dhcp_option_t *) dhcp->options;
while (o->option != 0xFF /* end of options */ &&
@@ -172,6 +238,14 @@
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;
c->retry_count = 0;
@@ -196,6 +270,8 @@
{
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);
dhcp_client_acquire_address (dcm, c);
/*
@@ -831,6 +907,7 @@
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);