Use Raw Sockets in Go for DHCP Packet Manipulation

Question:

Can raw sockets be used in Go to set a custom IP source address for DHCP packets?

Answer:

Yes, raw sockets are required to modify the IP source address of DHCP packets.

Security Considerations

Warning: Manipulating raw packets can have serious security implications. Running applications with root privileges or CAP_NET_RAW capability is necessary.

Raw Sockets in Go

The standard net library in Go does not support raw sockets due to its specialized nature and potential API changes. However, the go.net subrepository provides the ipv4 package for this purpose.

Packet Manipulation

To manipulate the DHCP packets, follow these steps:

1. Use ipv4.RawConn.ReadFrom() to receive the source packet.
2. Parse the packet header and payload.
3. Modify the header fields, including the source IP address based on the GIADDR field.
4. Use ipv4.RawConn.WriteTo() to forward the modified packet with the custom source IP address.

Example:

import "code.google.com/p/go.net/ipv4"

func main() {
  conn, err := ipv4.NewRawConn("udp")
  defer conn.Close()

  buf := make([]byte, 65536)
  for {
    hdr, payload, _, err := conn.ReadFrom(buf)
    if err != nil { ... }
    hdr.ID = 0
    hdr.Checksum = 0
    hdr.Dst = ...
    if err := conn.WriteTo(hdr, payload, nil); err != nil { ... }
  }
}