diff --git a/include/ip.h b/include/ip.h
index 2ca3fdd..842e90c 100644
--- a/include/ip.h
+++ b/include/ip.h
@@ -39,7 +39,6 @@ namespace Tins {
         
         /* Virtual methods */
         uint32_t header_size() const;
-        void write_serialization(uint8_t *buffer, uint32_t total_sz);
     private:
         struct iphdr {
         #if __BYTE_ORDER == __LITTLE_ENDIAN
@@ -63,6 +62,9 @@ namespace Tins {
             /*The options start here. */
         } __attribute__((packed));
         
+        void init_ip_fields();
+        void write_serialization(uint8_t *buffer, uint32_t total_sz);
+        
         iphdr _ip;
     };
 };
diff --git a/src/ip.cpp b/src/ip.cpp
index 4b0693d..a27a8b1 100644
--- a/src/ip.cpp
+++ b/src/ip.cpp
@@ -10,19 +10,28 @@ using namespace std;
 
 
 Tins::IP::IP(const string &ip_dst, const string &ip_src) : PDU(IPPROTO_IP) {
-    memset(&_ip, 0, sizeof(iphdr));
+    init_ip_fields();
     if(ip_dst.size())
         _ip.daddr = Utils::ip_to_int(ip_dst);
     if(ip_src.size())
         _ip.saddr = Utils::ip_to_int(ip_src);
+    
 }
 
 Tins::IP::IP(uint32_t ip_dst, uint32_t ip_src) : PDU(IPPROTO_IP) {
-    memset(&_ip, 0, sizeof(iphdr));
+    init_ip_fields();
     _ip.daddr = ip_dst;
     _ip.saddr = ip_src;
 }
 
+void Tins::IP::init_ip_fields() {
+    memset(&_ip, 0, sizeof(iphdr));
+    _ip.version = 4;
+    _ip.ihl = sizeof(iphdr) / sizeof(uint32_t);
+}
+
+/* Setters */
+
 void Tins::IP::tos(uint8_t new_tos) {
     _ip.tos = new_tos;
 }
@@ -67,11 +76,20 @@ void Tins::IP::dest_address(uint32_t ip) {
     _ip.daddr = ip;
 }
 
+/* Virtual method overriding. */
+
 uint32_t Tins::IP::header_size() const {
     return sizeof(iphdr);
 }
 
 void Tins::IP::write_serialization(uint8_t *buffer, uint32_t total_sz) {
-    assert(total_sz >= sizeof(iphdr));
+    uint32_t my_sz = header_size() + trailer_size(), new_flag = inner_pdu()->flag();
+    assert(total_sz >= my_sz);
+    if(new_flag == IPPROTO_IP)
+        new_flag = IPPROTO_IPIP;
+    flag(new_flag);
+    _ip.protocol = new_flag;
+    _ip.tot_len = total_sz;
     memcpy(buffer, &_ip, sizeof(iphdr));
+    /* IP Options here... */
 }
diff --git a/src/pdu.cpp b/src/pdu.cpp
index 8c2ba90..aef15bb 100644
--- a/src/pdu.cpp
+++ b/src/pdu.cpp
@@ -37,10 +37,10 @@ uint8_t *Tins::PDU::serialize(uint32_t &sz) {
 
 void Tins::PDU::serialize(uint8_t *buffer, uint32_t total_sz) {
     uint32_t sz = header_size() + trailer_size();
-    write_serialization(buffer, total_sz);
     /* Must not happen... */
     assert(total_sz >= sz);
     if(_inner_pdu)
         _inner_pdu->serialize(buffer + header_size(), total_sz - sz);
+    write_serialization(buffer, total_sz);
 }