Can Go\'s Raw Sockets Modify DHCP Discoveries with Custom Source IPs?

Using Raw Sockets in Go: Forwarding DHCP Discoveries

In an attempt to modify DHCP discoveries with a custom source IP address based on the GIADDR field, a developer has encountered difficulties using IP addresses that are not configured locally. This question arises:

Is it only possible to achieve this using raw sockets?

Answer:

Modifying the source IP address requires specific capabilities due to security considerations. To overcome this limitation, raw sockets can be utilized.

Go's Raw Socket Library:

While Go's standard net library does not provide raw socket support, the go.net subrepository offers both ipv4 and ipv6 packages. The ipv4 package, specifically its NewRawConn function, is suitable for this scenario.

Packet Manipulation:

To read and modify the packet headers, the ipv4.RawConn's ReadFrom method can be employed. Using the extracted fields and GIADDR logic, headers must be updated before initiating the WriteTo call.

Example:

<code class="go">for {
  hdr, payload, _, err := conn.ReadFrom(buf)
  if err != nil { ... }
  hdr.ID = 0
  hdr.Checksum = 0
  hdr.Src = ...
  hdr.Dst = ...
  if err := conn.WriteTo(hdr, payload, nil); err != nil { ... }
}</code>

This approach allows for modifying the source IP address based on specific conditions in the DHCP packet.

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