diff --git a/ipv4/gen.go b/ipv4/gen.go
new file mode 100644
index 0000000..673065f
--- /dev/null
+++ b/ipv4/gen.go
@@ -0,0 +1,242 @@
+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+
+// This program generates internet protocol constatns and tables by
+// reading IANA protocol registries.
+//
+// Usage of this program:
+//	go run gen.go > iana.go
+package main
+
+import (
+	"bytes"
+	"encoding/xml"
+	"fmt"
+	"go/format"
+	"io"
+	"net/http"
+	"os"
+	"strconv"
+	"strings"
+)
+
+var registries = []struct {
+	url   string
+	parse func(io.Writer, io.Reader) error
+}{
+	{
+		"http://www.iana.org/assignments/icmp-parameters",
+		parseICMPv4Parameters,
+	},
+	{
+		"http://www.iana.org/assignments/protocol-numbers/protocol-numbers.xml",
+		parseProtocolNumbers,
+	},
+}
+
+func main() {
+	var bb bytes.Buffer
+	fmt.Fprintf(&bb, "// go run gen.go\n")
+	fmt.Fprintf(&bb, "// GENERATED BY THE COMMAND ABOVE; DO NOT EDIT\n\n")
+	fmt.Fprintf(&bb, "package ipv4\n\n")
+	for _, r := range registries {
+		resp, err := http.Get(r.url)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		defer resp.Body.Close()
+		if resp.StatusCode != http.StatusOK {
+			fmt.Fprintf(os.Stderr, "got HTTP status code %v for %v\n", resp.StatusCode, r.url)
+			os.Exit(1)
+		}
+		if err := r.parse(&bb, resp.Body); err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		fmt.Fprintf(&bb, "\n")
+	}
+	b, err := format.Source(bb.Bytes())
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	os.Stdout.Write(b)
+}
+
+func parseICMPv4Parameters(w io.Writer, r io.Reader) error {
+	dec := xml.NewDecoder(r)
+	var icp icmpv4Parameters
+	if err := dec.Decode(&icp); err != nil {
+		return err
+	}
+	prs := icp.escape(0)
+	fmt.Fprintf(w, "// %s, Updated: %s\n", icp.Title, icp.Updated)
+	fmt.Fprintf(w, "const (\n")
+	for _, pr := range prs {
+		if pr.Descr == "" {
+			continue
+		}
+		fmt.Fprintf(w, "ICMPType%s ICMPType = %d", pr.Descr, pr.Value)
+		fmt.Fprintf(w, "// %s\n", pr.OrigDescr)
+	}
+	fmt.Fprintf(w, ")\n\n")
+	fmt.Fprintf(w, "// %s, Updated: %s\n", icp.Title, icp.Updated)
+	fmt.Fprintf(w, "var icmpTypes = map[ICMPType]string{\n")
+	for _, pr := range prs {
+		if pr.Descr == "" {
+			continue
+		}
+		fmt.Fprintf(w, "%d: %q,\n", pr.Value, strings.ToLower(pr.OrigDescr))
+	}
+	fmt.Fprintf(w, "}\n")
+	return nil
+}
+
+type icmpv4Parameters struct {
+	XMLName    xml.Name              `xml:"registry"`
+	Title      string                `xml:"title"`
+	Updated    string                `xml:"updated"`
+	Registries []icmpv4ParamRegistry `xml:"registry"`
+}
+
+type icmpv4ParamRegistry struct {
+	Title   string              `xml:"title"`
+	Records []icmpv4ParamRecord `xml:"record"`
+}
+
+type icmpv4ParamRecord struct {
+	Value string `xml:"value"`
+	Descr string `xml:"description"`
+}
+
+type canonICMPv4ParamRecord struct {
+	OrigDescr string
+	Descr     string
+	Value     int
+}
+
+func (icp *icmpv4Parameters) escape(id int) []canonICMPv4ParamRecord {
+	prs := make([]canonICMPv4ParamRecord, len(icp.Registries[id].Records))
+	sr := strings.NewReplacer(
+		"Messages", "",
+		"Message", "",
+		"ICMP", "",
+		"+", "P",
+		"-", "",
+		"/", "",
+		".", "",
+		" ", "",
+	)
+	for i, pr := range icp.Registries[id].Records {
+		if strings.Contains(pr.Descr, "Reserved") ||
+			strings.Contains(pr.Descr, "Unassigned") ||
+			strings.Contains(pr.Descr, "Deprecated") ||
+			strings.Contains(pr.Descr, "Experiment") ||
+			strings.Contains(pr.Descr, "experiment") {
+			continue
+		}
+		ss := strings.Split(pr.Descr, "\n")
+		if len(ss) > 1 {
+			prs[i].Descr = strings.Join(ss, " ")
+		} else {
+			prs[i].Descr = ss[0]
+		}
+		s := strings.TrimSpace(prs[i].Descr)
+		prs[i].OrigDescr = s
+		prs[i].Descr = sr.Replace(s)
+		prs[i].Value, _ = strconv.Atoi(pr.Value)
+	}
+	return prs
+}
+
+func parseProtocolNumbers(w io.Writer, r io.Reader) error {
+	dec := xml.NewDecoder(r)
+	var pn protocolNumbers
+	if err := dec.Decode(&pn); err != nil {
+		return err
+	}
+	prs := pn.escape()
+	prs = append([]canonProtocolRecord{{
+		Name:  "IP",
+		Descr: "IPv4 encapsulation, pseudo protocol number",
+		Value: 0,
+	}}, prs...)
+	fmt.Fprintf(w, "// %s, Updated: %s\n", pn.Title, pn.Updated)
+	fmt.Fprintf(w, "const (\n")
+	for _, pr := range prs {
+		if pr.Name == "" {
+			continue
+		}
+		fmt.Fprintf(w, "ianaProtocol%s = %d", pr.Name, pr.Value)
+		s := pr.Descr
+		if s == "" {
+			s = pr.OrigName
+		}
+		fmt.Fprintf(w, "// %s\n", s)
+	}
+	fmt.Fprintf(w, ")\n")
+	return nil
+}
+
+type protocolNumbers struct {
+	XMLName  xml.Name         `xml:"registry"`
+	Title    string           `xml:"title"`
+	Updated  string           `xml:"updated"`
+	RegTitle string           `xml:"registry>title"`
+	Note     string           `xml:"registry>note"`
+	Records  []protocolRecord `xml:"registry>record"`
+}
+
+type protocolRecord struct {
+	Value string `xml:"value"`
+	Name  string `xml:"name"`
+	Descr string `xml:"description"`
+}
+
+type canonProtocolRecord struct {
+	OrigName string
+	Name     string
+	Descr    string
+	Value    int
+}
+
+func (pn *protocolNumbers) escape() []canonProtocolRecord {
+	prs := make([]canonProtocolRecord, len(pn.Records))
+	sr := strings.NewReplacer(
+		"-in-", "in",
+		"-within-", "within",
+		"-over-", "over",
+		"+", "P",
+		"-", "",
+		"/", "",
+		".", "",
+		" ", "",
+	)
+	for i, pr := range pn.Records {
+		prs[i].OrigName = pr.Name
+		s := strings.TrimSpace(pr.Name)
+		switch pr.Name {
+		case "ISIS over IPv4":
+			prs[i].Name = "ISIS"
+		case "manet":
+			prs[i].Name = "MANET"
+		default:
+			prs[i].Name = sr.Replace(s)
+		}
+		ss := strings.Split(pr.Descr, "\n")
+		for i := range ss {
+			ss[i] = strings.TrimSpace(ss[i])
+		}
+		if len(ss) > 1 {
+			prs[i].Descr = strings.Join(ss, " ")
+		} else {
+			prs[i].Descr = ss[0]
+		}
+		prs[i].Value, _ = strconv.Atoi(pr.Value)
+	}
+	return prs
+}