--- udp_orig.c  2018-01-18 14:17:00.219413603 +0000
+++ udp.c   2018-01-18 16:03:21.633650570 +0000
@@ -1,20 +1,25 @@
-#include <unistd.h>
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
 #include <sys/socket.h>
+#include <arpa/inet.h>
+#include <netinet/in.h>
 #include <netinet/ip.h>
 #include <netinet/udp.h>

 // The packet length
 #define PCKT_LEN 8192

+#pragma pack(push, 1)
+
 // Can create separate header file (.h) for all headers' structure
 // The IP header's structure
 struct ipheader {
-    unsigned char      iph_ihl:5, iph_ver:4;
+    unsigned char      iph_ihl:4, iph_ver:4;
     unsigned char      iph_tos;
     unsigned short int iph_len;
     unsigned short int iph_ident;
-    unsigned char      iph_flag;
     unsigned short int iph_offset;
     unsigned char      iph_ttl;
     unsigned char      iph_protocol;
@@ -31,6 +36,8 @@
     unsigned short int udph_chksum;
 };

+#pragma pack(pop)
+
 // total udp header length: 8 bytes (=64 bits)
 // Function for checksum calculation. From the RFC,
 // the checksum algorithm is:
@@ -98,7 +105,7 @@
 ip->iph_ihl = 5;
 ip->iph_ver = 4;
 ip->iph_tos = 16; // Low delay
-ip->iph_len = sizeof(struct ipheader) + sizeof(struct udpheader);
+ip->iph_len = htons(sizeof(struct ipheader) + sizeof(struct udpheader));
 ip->iph_ident = htons(54321);
 ip->iph_ttl = 64; // hops
 ip->iph_protocol = 17; // UDP
@@ -117,7 +124,7 @@
 udp->udph_len = htons(sizeof(struct udpheader));

 // Calculate the checksum for integrity
-ip->iph_chksum = csum((unsigned short *)buffer, sizeof(struct ipheader) + sizeof(struct udpheader));
+ip->iph_chksum = htons(csum((unsigned short *)buffer, sizeof(struct ipheader) + sizeof(struct udpheader)));

 // Inform the kernel do not fill up the packet structure. we will build our own...
 if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) < 0){