How to Forward DHCP Discoveries using Raw Sockets in Go?

Raw Sockets in Go: A Guide to Forging IP Headers for DHCP Discovery Forwarding

This article addresses the challenge of utilizing raw sockets in Go to achieve the following: receiving DHCP discoveries (UDP), forwarding them to a specified IP address, and adjusting the source IP address based on specific DHCP packet field content (GIADDR).

Using Raw Sockets: A Necessity

To accomplish this task, raw sockets are indeed necessary. Standard IP addresses cannot be used as source addresses for packets unless they are configured on the local machine.

Examples in Go

The "go.net" subrepository provides a specialized package for raw socket handling:

http://godoc.org/code.google.com/p/go.net/ipv4#NewRawConn

Security Considerations

It is crucial to be aware of the potential security risks associated with manipulating source IP addresses. Operating with root privileges or applications with the CAP_NET_RAW capability is often necessary to enable this functionality.

Implementation Details

To set up raw socket handling and modify IP headers, follow these steps:

1. Import the "go.net/ipv4" package.
2. Create a new raw connection using ipv4.NewRawConn.
3. Use the ReadFrom method to receive DHCP packets.
4. Modify the packet headers according to your GIADDR logic.
5. Use the WriteTo method to forward the packet with the modified headers.

Remember to set the header fields to appropriate values:

hdr.ID = 0
hdr.Checksum = 0
hdr.Src = ...
hdr.Dst = ...

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