func pkt(ip [4]byte) []byte {
h := ipv4.Header{
Version: 4,
Len: 20,
TotalLen: 20 + 10, // 20 bytes for IP, 10 for ICMP
TTL: 64,
Protocol: 1, // ICMP
Dst: net.IPv4(ip[0], ip[1], ip[2], ip[3]),
// ID, Src and Checksum will be set for us by the kernel
}
icmp := []byte{
8, // type: echo request
0, // code: not used by echo request
0, // checksum (16 bit), we fill in below
0,
0, // identifier (16 bit). zero allowed.
0,
0, // sequence number (16 bit). zero allowed.
0,
0xC0, // Optional data. ping puts time packet sent here
0xDE,
}
cs := csum(icmp)
icmp[2] = byte(cs)
icmp[3] = byte(cs >> 8)
out, err := h.Marshal()
if err != nil {
glog.Error(err)
}
return append(out, icmp...)
}
