+#define IP_DF 0x4000 /* don't fragment */
+
+always_inline void *
+vlib_buffer_push_ip4_custom (vlib_main_t * vm, vlib_buffer_t * b,
+ ip4_address_t * src, ip4_address_t * dst,
+ int proto, u8 csum_offload, u8 is_df)
+{
+ ip4_header_t *ih;
+
+ /* make some room */
+ ih = vlib_buffer_push_uninit (b, sizeof (ip4_header_t));
+
+ ih->ip_version_and_header_length = 0x45;
+ ih->tos = 0;
+ ih->length = clib_host_to_net_u16 (vlib_buffer_length_in_chain (vm, b));
+
+ /* No fragments */
+ ih->flags_and_fragment_offset = is_df ? clib_host_to_net_u16 (IP_DF) : 0;
+ ih->ttl = 255;
+ ih->protocol = proto;
+ ih->src_address.as_u32 = src->as_u32;
+ ih->dst_address.as_u32 = dst->as_u32;
+
+ vnet_buffer (b)->l3_hdr_offset = (u8 *) ih - b->data;
+ b->flags |= VNET_BUFFER_F_IS_IP4 | VNET_BUFFER_F_L3_HDR_OFFSET_VALID;
+
+ /* Offload ip4 header checksum generation */
+ if (csum_offload)
+ {
+ ih->checksum = 0;
+ b->flags |= VNET_BUFFER_F_OFFLOAD_IP_CKSUM;
+ }
+ else
+ ih->checksum = ip4_header_checksum (ih);
+
+ return ih;
+}
+
+/**
+ * Push IPv4 header to buffer
+ *
+ * This does not support fragmentation.
+ *
+ * @param vm - vlib_main
+ * @param b - buffer to write the header to
+ * @param src - source IP
+ * @param dst - destination IP
+ * @param prot - payload proto
+ *
+ * @return - pointer to start of IP header
+ */
+always_inline void *
+vlib_buffer_push_ip4 (vlib_main_t * vm, vlib_buffer_t * b,
+ ip4_address_t * src, ip4_address_t * dst, int proto,
+ u8 csum_offload)
+{
+ return vlib_buffer_push_ip4_custom (vm, b, src, dst, proto, csum_offload,
+ 1 /* is_df */ );
+}
+
+always_inline u32
+vlib_buffer_get_ip4_fib_index (vlib_buffer_t * b)
+{
+ u32 fib_index, sw_if_index;
+ sw_if_index = vnet_buffer (b)->sw_if_index[VLIB_RX];
+ fib_index = vnet_buffer (b)->sw_if_index[VLIB_TX];
+ return (fib_index == (u32) ~ 0) ?
+ vec_elt (ip4_main.fib_index_by_sw_if_index, sw_if_index) : fib_index;
+}