diff --git a/CHANGELOG.md b/CHANGELOG.md
index 872791ec4..e32bc1b97 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Add alternative for supporting snmp during scans. [#594](https://github.com/greenbone/openvas/pull/594)
 - Add resolve_hostname_to_multiple_ips() NASL function. [#596](https://github.com/greenbone/openvas/pull/596)
 - Send message to the client with hosts count. [#606](https://github.com/greenbone/openvas/pull/606)
+- Use nasl_perror on invalid input and add more documentation. [#608](https://github.com/greenbone/openvas/pull/608)
 
 ### Changed
 - Downgrade wmi queries log level for common errors.
diff --git a/nasl/nasl_packet_forgery.c b/nasl/nasl_packet_forgery.c
index 56196575d..8df05313f 100644
--- a/nasl/nasl_packet_forgery.c
+++ b/nasl/nasl_packet_forgery.c
@@ -86,6 +86,29 @@ int n;
 
 /*--------------[ IP ]--------------------------------------------*/
 
+/**
+ * @brief Forge an IP datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] data    Payload.
+ * @param[in] ip_hl   IP header length in 32 bits words. 5 by default.
+ * @param[in] ip_id   Datagram ID. Random by default.
+ * @param[in] ip_len  Length of the datagram. 20 plus the length of the data
+ * field by default.
+ * @param[in] ip_off  Fragment offset in 64 bits words. 0 by default.
+ * @param[in] ip_p    IP protocol. 0 by default.
+ * @param[in] ip_src  Source address in ASCII. NASL will convert it into an
+ * integer in network order.
+ * @param[in] ip_dst  Destination address in ASCII. NASL will convert it into an
+ * integer in network order. Uses the target ip of the current plugin by
+ * default.
+ * @param[in] ip_sum  Packet header checksum. It will be computed by default.
+ * @param[in] ip_tos  Type of service field. 0 by default
+ * @param[in] ip_ttl  Time To Live field. 64 by default.
+ * @param[in] ip_v    IP version. 4 by default.
+ *
+ * @return The forged IP packet.
+ */
 tree_cell *
 forge_ip_packet (lex_ctxt *lexic)
 {
@@ -100,7 +123,11 @@ forge_ip_packet (lex_ctxt *lexic)
   dst_addr = plug_get_host_ip (script_infos);
 
   if (dst_addr == NULL || (IN6_IS_ADDR_V4MAPPED (dst_addr) != 1))
-    return NULL;
+    {
+      nasl_perror (lexic, "forge_ip_packet: No valid dst_addr could be "
+                          "determined via call to plug_get_host_ip().\n");
+      return NULL;
+    }
 
   data = get_str_var_by_name (lexic, "data");
   data_len = get_var_size_by_name (lexic, "data");
@@ -152,6 +179,15 @@ forge_ip_packet (lex_ctxt *lexic)
   return retc;
 }
 
+/**
+ * @brief Extracts a field from an IP datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] element Name of the field, e.g. "ip_len" or "ip_src".
+ * @param[in] ip      IP datagram or fragment.
+ *
+ * @return  integer or a string, depending on the type of the element.
+ */
 tree_cell *
 get_ip_element (lex_ctxt *lexic)
 {
@@ -240,7 +276,7 @@ get_ip_element (lex_ctxt *lexic)
 
   if (flag == 0)
     {
-      printf ("%s : unknown element\n", element);
+      nasl_perror (lexic, "%s: unknown element '%s'\n", __func__, element);
       return NULL;
     }
 
@@ -251,6 +287,26 @@ get_ip_element (lex_ctxt *lexic)
   return retc;
 }
 
+/**
+ * @brief Modify the fields of a datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] ip      IP datagram to set fields on.
+ * @param[in] ip_hl   IP header length in 32 bits words. 5 by default.
+ * @param[in] ip_id   Datagram ID. Random by default.
+ * @param[in] ip_len  Length of the datagram. 20 plus the length of the data
+ * field by default.
+ * @param[in] ip_off  Fragment offset in 64 bits words. 0 by default.
+ * @param[in] ip_p    IP protocol. 0 by default.
+ * @param[in] ip_src  Source address in ASCII. NASL will convert it into an
+ * integer in network order.
+ * @param[in] ip_sum  Packet header checksum. It will be computed by default.
+ * @param[in] ip_tos  Type of service field. 0 by default
+ * @param[in] ip_ttl  Time To Live field. 64 by default.
+ * @param[in] ip_v    IP version. 4 by default.
+ *
+ * @return The modified IP datagram.
+ */
 tree_cell *
 set_ip_elements (lex_ctxt *lexic)
 {
@@ -295,6 +351,17 @@ set_ip_elements (lex_ctxt *lexic)
   return retc;
 }
 
+/**
+ * @brief Add option datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] ip      IP datagram to add the option to.
+ * @param[in] code    Number of the option.
+ * @param[in] length  Length of the option data.
+ * @param[in] value   Option data.
+ *
+ * @return The modified IP datagram.
+ */
 tree_cell *
 insert_ip_options (lex_ctxt *lexic)
 {
@@ -366,6 +433,12 @@ insert_ip_options (lex_ctxt *lexic)
   return retc;
 }
 
+/**
+ * @brief Dump IP datagrams.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] ...     IP datagrams to dump.
+ */
 tree_cell *
 dump_ip_packet (lex_ctxt *lexic)
 {
@@ -423,6 +496,33 @@ struct pseudohdr
   struct tcphdr tcpheader;
 };
 
+/**
+ * @brief Fills an IP datagram with TCP data. Note that the ip_p field is not
+ updated. It returns the modified IP datagram. Its arguments are:
+
+ * @param[in] ip        IP datagram to be filled.
+ * @param[in] data      TCP data payload.
+ * @param[in] th_ack    Acknowledge number. NASL will convert it into network
+ order if necessary. 0 by default.
+ * @param[in] th_dport  Destination port. NASL will convert it into network
+ order if necessary. 0 by default.
+ * @param[in] th_flags  TCP flags. 0 by default.
+ * @param[in] th_off    Size of the TCP header in 32 bits words. By default, 5.
+ * @param[in] th_seq    TCP sequence number. NASL will convert it into network
+ order if necessary. Random by default.
+ * @param[in] th_sport  Source port. NASL will convert it into network order if
+ necessary. 0 by default.
+ * @param[in] th_sum    TCP checksum. Right value is computed by default.
+ * @param[in] th_urp    Urgent pointer. 0 by default.
+ * @param[in] th_win    TCP window size. NASL will convert it into network order
+ if necessary. 0 by default.
+ * @param[in] th_x2           Is a reserved field and should probably be left
+ unchanged. 0 by default.
+ * @param[in] update_ip_len   Flag (TRUE by default). If set, NASL will
+ recompute the size field of the IP datagram.
+ *
+ * @return Modified IP datagram.
+ */
 tree_cell *
 forge_tcp_packet (lex_ctxt *lexic)
 {
@@ -511,6 +611,15 @@ forge_tcp_packet (lex_ctxt *lexic)
   return retc;
 }
 
+/**
+ * @brief Extracts TCP field from an IP datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] element Name of the the TCP field. See forge_tcp_packet().
+ * @param[in] tcp     The full IP datagram (IP + TCP).
+ *
+ * @return  Data block or an integer, according to the type of the element.
+ */
 tree_cell *
 get_tcp_element (lex_ctxt *lexic)
 {
@@ -586,6 +695,33 @@ get_tcp_element (lex_ctxt *lexic)
   return retc;
 }
 
+/**
+ * @brief Modify the TCP fields of a datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] tcp       IP datagram.
+ * @param[in] data      TCP data payload.
+ * @param[in] th_ack    Acknowledge number. NASL will convert it into network
+ * order if necessary.
+ * @param[in] th_dport  Destination port. NASL will convert it into network
+ * order if necessary.
+ * @param[in] th_flags  TCP flags.
+ * @param[in] th_off    Size of the TCP header in 32 bits words.
+ * @param[in] th_seq    TCP sequence number. NASL will convert it into network
+ * order if necessary.
+ * @param[in] th_sport  Source port. NASL will convert it into network order
+ * if necessary.
+ * @param[in] th_sum    TCP checksum.
+ * @param[in] th_urp    Urgent pointer.
+ * @param[in] th_win    TCP window size. NASL will convert it into network
+ * order if necessary.
+ * @param[in] th_x2           Is a reserved field and should probably be left
+ * unchanged.
+ * @param[in] update_ip_len   Flag (TRUE by default). If set, NASL will
+ * recompute the size field of the IP datagram.
+ *
+ * @return The modified IP datagram.
+ */
 tree_cell *
 set_tcp_elements (lex_ctxt *lexic)
 {
@@ -682,6 +818,12 @@ set_tcp_elements (lex_ctxt *lexic)
   return retc;
 }
 
+/**
+ * @brief Dump the TCP part of a IP Datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] ...     IP datagrams to dump the TCP part from.
+ */
 tree_cell *
 dump_tcp_packet (lex_ctxt *lexic)
 {
@@ -778,6 +920,25 @@ struct pseudo_udp_hdr
   struct udphdr udpheader;
 };
 
+/**
+ * @brief Fills an IP datagram with UDP data. Note that the ip_p field is not
+ updated. It returns the modified IP datagram. Its arguments are:
+
+ * @param[in] ip            IP datagram to be filled.
+ * @param[in] data          Payload.
+ * @param[in] uh_dport      Destination port. NASL will convert it into network
+ order if necessary. 0 by default.
+ * @param[in] uh_sport      Source port. NASL will convert it into network order
+ if necessary. 0 by default.
+ * @param[in] uh_sum        UDP checksum. Although it is not compulsary, the
+ right value is computed by default.
+ * @param[in] uh_ulen       Data length. By default it is set to the length of
+ the data argument plus the size of the UDP header.
+ * @param[in] update_ip_len Flag (TRUE by default). If set, NASL will recompute
+ the size field of the IP datagram.
+ *
+ * @return Modified IP datagram.
+ */
 tree_cell *
 forge_udp_packet (lex_ctxt *lexic)
 {
@@ -856,11 +1017,21 @@ forge_udp_packet (lex_ctxt *lexic)
       return retc;
     }
   else
-    printf ("Error ! You must supply the 'ip' argument !\n");
+    nasl_perror (lexic,
+                 "forge_udp_packet: Invalid value for the argument 'ip'\n");
 
   return NULL;
 }
 
+/**
+ * @brief Get an UDP element from a IP datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] udp     The full IP datagram (IP + UDP).
+ * @param[in] element Name of the UDP field (see forge_udp_packet()).
+ *
+ * @return  Data block or an integer, according to the type of the element.
+ */
 tree_cell *
 get_udp_element (lex_ctxt *lexic)
 {
@@ -878,8 +1049,8 @@ get_udp_element (lex_ctxt *lexic)
   element = get_str_var_by_name (lexic, "element");
   if (udp == NULL || element == NULL)
     {
-      printf ("get_udp_element() usage :\n");
-      printf ("element = get_udp_element(udp:<udp>,element:<element>\n");
+      nasl_perror (lexic, "get_udp_element: usage :\nelement = "
+                          "get_udp_element(udp:<udp>,element:<element>\n");
       return NULL;
     }
   ip = (struct ip *) udp;
@@ -913,7 +1084,8 @@ get_udp_element (lex_ctxt *lexic)
     }
   else
     {
-      printf ("%s is not a value of a udp packet\n", element);
+      nasl_perror (lexic, "%s: '%s' is not a value of a udp packet\n", __func__,
+                   element);
       return NULL;
     }
 
@@ -922,6 +1094,20 @@ get_udp_element (lex_ctxt *lexic)
   return retc;
 }
 
+/**
+ * @brief Modify UDP fields of an IP datagram.
+ *
+ * @param[in] udp   IP datagram to modify.
+ * @param[in] data          Payload.
+ * @param[in] uh_dport      Destination port. NASL will convert it into network
+ * order if necessary.
+ * @param[in] uh_sport      Source port. NASL will convert it into network order
+ * if necessary.
+ * @param[in] uh_sum        UDP checksum.
+ * @param[in] uh_ulen       Data length.
+ *
+ * @return Modified IP datagram.
+ */
 tree_cell *
 set_udp_elements (lex_ctxt *lexic)
 {
@@ -1022,11 +1208,18 @@ set_udp_elements (lex_ctxt *lexic)
       return retc;
     }
   else
-    printf ("Error ! You must supply the 'udp' argument !\n");
+    nasl_perror (lexic,
+                 "set_udp_elements:  Invalid value for the argument 'udp'.");
 
   return NULL;
 }
 
+/**
+ * @brief Dump the UDP part of a IP Datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] ...     IP datagrams to dump the UDP part from.
+ */
 tree_cell *
 dump_udp_packet (lex_ctxt *lexic)
 {
@@ -1057,6 +1250,21 @@ dump_udp_packet (lex_ctxt *lexic)
 
 /*--------------[  ICMP  ]--------------------------------------------*/
 
+/**
+ * @brief Fill an IP datagram with ICMP data.
+ *
+ * @param[in] lexic         Lexical context of NASL interpreter.
+ * @param[in] ip            IP datagram that is updated.
+ * @param[in] data          Payload.
+ * @param[in] icmp_cksum    Checksum, computed by default.
+ * @param[in] icmp_code     ICMP code. 0 by default.
+ * @param[in] icmp_id       ICMP ID. 0 by default.
+ * @param[in] icmp_seq      ICMP sequence number.
+ * @param[in] icmp_type     ICMP type. 0  * @param[in]  update_ip_len Flag (TRUE
+ * by default). If set, NASL will recompute the size field of the IP datagram.
+ *
+ * @return Modified IP datagram.
+ */
 tree_cell *
 forge_icmp_packet (lex_ctxt *lexic)
 {
@@ -1124,6 +1332,15 @@ forge_icmp_packet (lex_ctxt *lexic)
   return retc;
 }
 
+/**
+ * @brief Get an ICMP element from a IP datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] icmp    Full IP datagram (IP + ICMP).
+ * @param[in] element Name of the TCP field (see forge_tcp_packet()).
+ *
+ * @return Data block or an integer, according to the type of the element.
+ */
 tree_cell *
 get_icmp_element (lex_ctxt *lexic)
 {
@@ -1140,7 +1357,11 @@ get_icmp_element (lex_ctxt *lexic)
       icmp = (struct icmp *) (p + ip->ip_hl * 4);
 
       if (elem == NULL)
-        return NULL;
+        {
+          nasl_perror (lexic,
+                       "get_icmp_element: missing 'element' parameter\n");
+          return NULL;
+        }
 
       if (!strcmp (elem, "icmp_id"))
         value = ntohs (icmp->icmp_id);
@@ -1168,12 +1389,20 @@ get_icmp_element (lex_ctxt *lexic)
           return retc;
         }
       else
-        return NULL;
+        {
+          nasl_perror (
+            lexic,
+            "get_icmp_element: Element '%s' is not a valid element to get.\n",
+            elem);
+          return NULL;
+        }
 
       retc = alloc_typed_cell (CONST_INT);
       retc->x.i_val = value;
       return retc;
     }
+  else
+    nasl_perror (lexic, "get_icmp_element: missing 'icmp' parameter\n");
 
   return NULL;
 }
@@ -1188,6 +1417,20 @@ struct igmp
   struct in_addr group;
 };
 
+/**
+ * @brief Fills an IP datagram with IGMP data.
+ *
+ * @param[in] lexic         Lexical context of NASL interpreter.
+ * @param[in] ip            IP datagram that is updated.
+ * @param[in] code          0 by default.
+ * @param[in] data
+ * @param[in] group
+ * @param[in] type          0 by default.
+ * @param[in] update_ip_len Flag (TRUE by default). If set, NASL will recompute
+ * the size field of the IP datagram.
+ *
+ * @return Modified IP datagram.
+ */
 tree_cell *
 forge_igmp_packet (lex_ctxt *lexic)
 {
@@ -1242,12 +1485,26 @@ forge_igmp_packet (lex_ctxt *lexic)
       retc->size = ip->ip_hl * 4 + sizeof (struct igmp) + len;
       return retc;
     }
+  else
+    nasl_perror (lexic, "forge_igmp_packet: missing 'ip' parameter\n");
 
   return NULL;
 }
 
 /*---------------------------------------------------------------------------*/
 
+/**
+ * @brief Lunches a “TCP ping” against the target host.
+ *
+ * Tries to open a TCP connection and sees if anything comes back (SYN/ACK or
+ * RST).
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] port    Port to ping. Internal list of common ports is used as
+ * default.
+ *
+ * @return 1 if Ping was successul, 0 else.
+ */
 tree_cell *
 nasl_tcp_ping (lex_ctxt *lexic)
 {
@@ -1387,6 +1644,21 @@ nasl_tcp_ping (lex_ctxt *lexic)
 
 /*---------------------------------------------------------------------------*/
 
+/**
+ * @brief Send a list of packets (passed as unnamed arguments) and listens to
+ * the answers. It returns a block made of all the sniffed “answers”.
+ *
+ * @param[in] lexic           Lexical context of NASL interpreter.
+ * @param[in] ...             Packets to send.
+ * @param[in] length          Length of each packet by default.
+ * @param[in] pcap_active     TRUE by default. Otherwise, NASL does not listen
+ * for the answers.
+ * @param[in] pcap_filter     BPF filter.
+ * @param[in] pcap_timeout    Capture timout. 5 by default.
+ * @param[in] allow_broadcast Default 0.
+ *
+ * @return block made of all the sniffed “answers”.
+ */
 tree_cell *
 nasl_send_packet (lex_ctxt *lexic)
 {
@@ -1512,6 +1784,17 @@ nasl_send_packet (lex_ctxt *lexic)
 
 /*---------------------------------------------------------------------------*/
 
+/**
+ * @brief Listen to one packet and return it.
+ *
+ * @param[in] lexic         Lexical context of NASL interpreter.
+ * @param[in] interface     Network interface name. By default, NASL will try to
+ * find the best one.
+ * @param[in] pcap_filter   BPF filter. By default, it listens to everything.
+ * @param[in] timeout       5 seconds by default.
+ *
+ * @return Packet which was captured.
+ */
 tree_cell *
 nasl_pcap_next (lex_ctxt *lexic)
 {
@@ -1653,6 +1936,15 @@ nasl_pcap_next (lex_ctxt *lexic)
   return retc;
 }
 
+/**
+ * @brief Send a capture.
+ *
+ * @param[in] interface string
+ * @param[in] pcap filter string
+ * @param[in] timeout integer
+ *
+ * @return Packet which was captured.
+ */
 tree_cell *
 nasl_send_capture (lex_ctxt *lexic)
 {
diff --git a/nasl/nasl_packet_forgery_v6.c b/nasl/nasl_packet_forgery_v6.c
index 9ade7b69e..2e5efc97d 100644
--- a/nasl/nasl_packet_forgery_v6.c
+++ b/nasl/nasl_packet_forgery_v6.c
@@ -108,12 +108,21 @@ int n;
 }
 
 /*--------------[ IP ]--------------------------------------------*/
+
 /**
- * @brief Forge IPv6 packet.
+ * @brief Forge an IPv6 packet.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic     Lexical context of NASL interpreter.
+ * @param[in] data      Data payload
+ * @param[in] ip6_v     Version. 6 by default.
+ * @param[in] ip6_tc    Traffic class. 0 by default.
+ * @param[in] ip6_fl    Flow label. 0 by default.
+ * @param[in] ip6_p     IP protocol. 0 by default.
+ * @param[in] ip6_hlim  Hop limit. Max. 255. 64 by default.
+ * @param[in] ip6_src   Source address.
+ * @param[in] ip6_dst   Destination address.
  *
- * @return tree_cell with the forged IP packet.
+ * @return Forged IP packet.
  */
 tree_cell *
 forge_ipv6_packet (lex_ctxt *lexic)
@@ -180,7 +189,9 @@ forge_ipv6_packet (lex_ctxt *lexic)
 /**
  * @brief Obtain IPv6 header element.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] ipv6    IP v6 header
+ * @param[in] element Element to extract from the header.
  *
  * @return tree_cell with the IP header element.
  */
@@ -257,7 +268,7 @@ get_ipv6_element (lex_ctxt *lexic)
 
   if (flag == 0)
     {
-      printf ("%s : unknown element\n", element);
+      nasl_perror (lexic, "%s : unknown element '%s'\n", __func__, element);
       return NULL;
     }
 
@@ -271,7 +282,12 @@ get_ipv6_element (lex_ctxt *lexic)
 /**
  * @brief Set IPv6 header element.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic     Lexical context of NASL interpreter.
+ * @param[in] ip6       IP v6 header.
+ * @param[in] ip6_plen  Payload lenght.
+ * @param[in] ip6_hlim  Hop limit. Max. 255
+ * @param[in] ip6_nxt   Next packet.
+ * @param[in] ip6_src   Source address
  *
  * @return tree_cell with the forged IP packet.
  */
@@ -311,7 +327,8 @@ set_ipv6_elements (lex_ctxt *lexic)
 /**
  * @brief Print IPv6 Header.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] ...     IPv6 datagrams to dump.
  *
  * @return Print and returns FAKE_CELL.
  */
@@ -361,6 +378,18 @@ dump_ipv6_packet (lex_ctxt *lexic)
   return FAKE_CELL;
 }
 
+/**
+ * @brief Adds an IPv6 option to the datagram.
+ *
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] ip6     IPv6 packet.
+ * @param[in] data    Data payload.
+ * @param[in] code    Code of option.
+ * @param[in] lenght  Length of value.
+ * @param[in] value   Value of the option.
+ *
+ * @return the modified datagram.
+ */
 tree_cell *
 insert_ipv6_options (lex_ctxt *lexic)
 {
@@ -442,7 +471,19 @@ struct v6pseudohdr
 /**
  * @brief Forge TCP packet.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic     Lexical context of NASL interpreter.
+ * @param[in] ip6       IPv6 packet.
+ * @param[in] data      Data.
+ * @param[in] th_sport  Source port. 0 by default.
+ * @param[in] th_dport  Destination port. 0 by default.
+ * @param[in] th_seq    Sequence number. Random by default.
+ * @param[in] th_ack    Acknowledgement number. 0 by default.
+ * @param[in] th_x2     0 by default.
+ * @param[in] th_off    Data offset. 5 by default.
+ * @param[in] th_flags  Flags. 0 by default.
+ * @param[in] th_win    Window. 0 by default.
+ * @param[in] th_sum    Checksum. Is filled in automatically by default
+ * @param[in] th_urp    Urgent pointer. 0 by default.
  *
  * @return tree_cell with the forged TCP packet containing IPv6 header.
  */
@@ -527,7 +568,10 @@ forge_tcp_v6_packet (lex_ctxt *lexic)
 /**
  * @brief Get TCP Header element.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] tcp     IPv6 packet
+ * @param[in] element Element to extract from the header (see
+ * forge_tcp_v6_packet()).
  *
  * @return tree_cell with the forged IP packet.
  */
@@ -616,9 +660,23 @@ get_tcp_v6_element (lex_ctxt *lexic)
 /**
  * @brief Set TCP Header element.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic     Lexical context of NASL interpreter.
+ * @param[in] tcp       IPv6 packet to modify.
+ * @param[in] data      Data.
+ * @param[in] th_sport  Source port.
+ * @param[in] th_dport  Destination port.
+ * @param[in] th_seq    Sequence number.
+ * @param[in] th_ack    Acknowledgement number.
+ * @param[in] th_x2
+ * @param[in] th_off    Data offset.
+ * @param[in] th_flags  Flags.
+ * @param[in] th_win    Window.
+ * @param[in] th_sum    Checksum.
+ * @param[in] th_urp    Urgent pointer.
+ * @param[in] update_ip_len  Flag (TRUE by default). If set, NASL will recompute
+ * the size field of the IP datagram.
  *
- * @return tree_cell with the forged TCP packet and IPv6.
+ * @return tree_cell with the modified IPv6 datagram.
  */
 tree_cell *
 set_tcp_v6_elements (lex_ctxt *lexic)
@@ -709,9 +767,10 @@ set_tcp_v6_elements (lex_ctxt *lexic)
 }
 
 /**
- * @brief Print TCP/IPv6 packet.
+ * @brief Dump TCP part of an IPv6 Datagram.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] ...     IPv6 datagrams to dump.
  *
  * @return Print and return FAKE_CELL.
  */
@@ -817,9 +876,16 @@ struct v6pseudo_udp_hdr
 };
 
 /*
- * @brief Forge v6 packet for UDP.
+ * @brief Fills an IPv6 datagram with UDP data.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic           Lexical context of NASL interpreter.
+ * @param[in] ip6             IPv6 packet.
+ * @param[in] data            Data.
+ * @param[in] uh_sport        Source port. 0 by default.
+ * @param[in] uh_dport        Destination port. 0 by default.
+ * @param[in] uh_ulen         Udp length.
+ * @param[in] update_ip6_len  Flag (TRUE by default). If set, NASL will
+ * recompute the size field of the IP datagram.
  *
  * @return tree_cell with the forged UDP packet containing IPv6 header.
  */
@@ -893,15 +959,17 @@ forge_udp_v6_packet (lex_ctxt *lexic)
       return retc;
     }
   else
-    printf ("Error ! You must supply the 'ip6' argument !\n");
+    nasl_perror (lexic, "forge_udp_v6_packet:'ip6' argument missing. \n");
 
   return NULL;
 }
 
 /*
- * @brief Get UDP Header element.
+ * @brief Get an UDP Header element.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] udp     IPv6 datagram.
+ * @param[in] element One of 'uh_sport', 'uh_dport', 'uh_ulen', 'uh_sum', 'data'
  *
  * @return tree_cell with the forged UDP packet.
  */
@@ -921,8 +989,9 @@ get_udp_v6_element (lex_ctxt *lexic)
   element = get_str_var_by_name (lexic, "element");
   if (udp == NULL || element == NULL)
     {
-      printf ("get_udp_v6_element() usage :\n");
-      printf ("element = get_udp_v6_element(udp:<udp>,element:<element>\n");
+      nasl_perror (
+        lexic, "get_udp_v6_element() usage :\n"
+               "element = get_udp_v6_element(udp:<udp>,element:<element>\n");
       return NULL;
     }
 
@@ -954,7 +1023,7 @@ get_udp_v6_element (lex_ctxt *lexic)
     }
   else
     {
-      printf ("%s is not a value of a udp packet\n", element);
+      nasl_perror (lexic, "%s is not a value of a udp packet\n", element);
       return NULL;
     }
 
@@ -966,7 +1035,13 @@ get_udp_v6_element (lex_ctxt *lexic)
 /*
  * @brief Set UDP Header element.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic     Lexical context of NASL interpreter
+ * @param[in] udp       IPv6 packet.
+ * @param[in] data      Data.
+ * @param[in] uh_sport  Source port.
+ * @param[in] uh_dport  Destination port.
+ * @param[in] uh_ulen   Udp length.
+ * @param[in] uh_sum    Checksum.
  *
  * @return tree_cell with the forged UDP packet and IPv6.
  */
@@ -1066,15 +1141,17 @@ set_udp_v6_elements (lex_ctxt *lexic)
       return retc;
     }
   else
-    printf ("Error ! You must supply the 'udp' argument !\n");
+    nasl_perror (lexic,
+                 "set_udp_v6_elements: You must supply the 'udp' argument !\n");
 
   return NULL;
 }
 
 /*
- * @brief Print UDP/IPv6 packet.
+ * @brief Print UDP part of IPv6 packet.
  *
  * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] ...   IPv6 datagrams to dump.
  *
  * @return Print and return FAKE_CELL.
  */
@@ -1127,6 +1204,18 @@ struct v6pseudo_icmp_hdr
  * @brief Forge ICMPv6 packet.
  *
  * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] ip6               IPv6 datagram to add ICMP header to.
+ * @param[in] data              Payload.
+ * @param[in] icmp_type         0 by default.
+ * @param[in] icmp_code         0 by default.
+ * @param[in] icmp_id           0 by default.
+ * @param[in] icmp_seq
+ * @param[in] reacheable_time
+ * @param[in] retransmit_timer
+ * @param[in] flags
+ * @param[in] target
+ * @param[in] update_ip_len
+ * @param[in] icmp_cksum
  *
  * @return tree_cell with the forged ICMPv6 packet containing IPv6 header.
  */
@@ -1378,7 +1467,10 @@ forge_icmp_v6_packet (lex_ctxt *lexic)
 /*
  * @brief Obtain ICMPv6 header element.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic   Lexical context of NASL interpreter.
+ * @param[in] icmp    IPV6 datagram.
+ * @param[in] element One of 'icmp_code', 'icmp_type', 'icmp_cksum', 'icmp_id',
+ * 'icmp_seq', 'data'
  *
  * @return tree_cell with the ICMPv6 header element.
  */
@@ -1397,7 +1489,10 @@ get_icmp_v6_element (lex_ctxt *lexic)
       icmp = (struct icmp6_hdr *) (p + 40);
 
       if (elem == NULL)
-        return NULL;
+        {
+          nasl_perror (lexic, "%s: Missing 'element' argument\n", __func__);
+          return NULL;
+        }
 
       else if (!strcmp (elem, "icmp_code"))
         value = icmp->icmp6_code;
@@ -1423,12 +1518,18 @@ get_icmp_v6_element (lex_ctxt *lexic)
           return retc;
         }
       else
-        return NULL;
+        {
+          nasl_perror (lexic, "%s: '%s' not a valid 'element' argument\n",
+                       __func__, elem);
+          return NULL;
+        }
 
       retc = alloc_typed_cell (CONST_INT);
       retc->x.i_val = value;
       return retc;
     }
+  else
+    nasl_perror (lexic, "%s: missing 'icmp' parameter\n", __func__);
 
   return NULL;
 }
@@ -1450,6 +1551,11 @@ struct igmp6_hdr
  * @brief Forge IGMPv6 packet.
  *
  * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] ip6   IPv6 datagram.
+ * @param[in] data
+ * @param[in] type
+ * @param[in] code
+ * @param[in] group
  *
  * @return tree_cell with the forged IGMPv6 packet containing IPv6 header.
  */
@@ -1504,6 +1610,8 @@ forge_igmp_v6_packet (lex_ctxt *lexic)
       retc->size = 40 + sizeof (struct igmp6_hdr) + len;
       return retc;
     }
+  else
+    nasl_perror (lexic, "forge_igmp_v6_packet: missing 'ip6' parameter\n");
 
   return NULL;
 }
@@ -1512,6 +1620,8 @@ forge_igmp_v6_packet (lex_ctxt *lexic)
  * @brief Performs TCP Connect to test if host is alive.
  *
  * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] port  Port to ping. Internal list of common ports is used as
+ * default.
  *
  * @return tree_cell > 0 if host is alive, 0 otherwise.
  */
@@ -1649,9 +1759,16 @@ nasl_tcp_v6_ping (lex_ctxt *lexic)
 }
 
 /**
- * @brief Send forged IPv6 Packet.
+ * @brief Send forged IPv6 Packets.
  *
- * @param[in] lexic Lexical context of NASL interpreter.
+ * @param[in] lexic           Lexical context of NASL interpreter.
+ * @param[in] ...             IPv6 packets to send.
+ * @param[in] length          Length of each packet by default.
+ * @param[in] pcap_active     TRUE by default. Otherwise, NASL does not listen
+ * for the answers.
+ * @param[in] pcap_filter     BPF filter.
+ * @param[in] pcap_timeout    Capture timout. 5 by default.
+ * @param[in] allow_multicast Default 0.
  *
  * @return tree_cell with the response to the sent packet.
  */