diff --git a/unum/vendor/golang.org/x/net/icmp/ipv4.go b/unum/vendor/golang.org/x/net/icmp/ipv4.go
new file mode 100644
index 0000000..ffc66ed
--- /dev/null
+++ b/unum/vendor/golang.org/x/net/icmp/ipv4.go
@@ -0,0 +1,61 @@
+// Copyright 2014 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.
+
+package icmp
+
+import (
+	"encoding/binary"
+	"net"
+	"runtime"
+
+	"golang.org/x/net/internal/socket"
+	"golang.org/x/net/ipv4"
+)
+
+// freebsdVersion is set in sys_freebsd.go.
+// See http://www.freebsd.org/doc/en/books/porters-handbook/freebsd-versions.html.
+var freebsdVersion uint32
+
+// ParseIPv4Header parses b as an IPv4 header of ICMP error message
+// invoking packet, which is contained in ICMP error message.
+func ParseIPv4Header(b []byte) (*ipv4.Header, error) {
+	if len(b) < ipv4.HeaderLen {
+		return nil, errHeaderTooShort
+	}
+	hdrlen := int(b[0]&0x0f) << 2
+	if hdrlen > len(b) {
+		return nil, errBufferTooShort
+	}
+	h := &ipv4.Header{
+		Version:  int(b[0] >> 4),
+		Len:      hdrlen,
+		TOS:      int(b[1]),
+		ID:       int(binary.BigEndian.Uint16(b[4:6])),
+		FragOff:  int(binary.BigEndian.Uint16(b[6:8])),
+		TTL:      int(b[8]),
+		Protocol: int(b[9]),
+		Checksum: int(binary.BigEndian.Uint16(b[10:12])),
+		Src:      net.IPv4(b[12], b[13], b[14], b[15]),
+		Dst:      net.IPv4(b[16], b[17], b[18], b[19]),
+	}
+	switch runtime.GOOS {
+	case "darwin":
+		h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4]))
+	case "freebsd":
+		if freebsdVersion >= 1000000 {
+			h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
+		} else {
+			h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4]))
+		}
+	default:
+		h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
+	}
+	h.Flags = ipv4.HeaderFlags(h.FragOff&0xe000) >> 13
+	h.FragOff = h.FragOff & 0x1fff
+	if hdrlen-ipv4.HeaderLen > 0 {
+		h.Options = make([]byte, hdrlen-ipv4.HeaderLen)
+		copy(h.Options, b[ipv4.HeaderLen:])
+	}
+	return h, nil
+}