Why does libpcap have a struct pcap_addr_t that uses sockaddr_in to define addresses on a device?

Question

I am curious as to why sockaddr is used inside pcap_addr_t which is given to you when calling pcap_findalldevs. The reason this is not so straight forward is because sockaddr_in contains information about the address and port. This is similar to .NET's System.Net.IPEndPoint class.

If we were looking at a .NET library, I would not expect to see a property such as that with a description about addresses belonging to a device. As far as I know, no protocols define an address and port when describing a device on a system.

On all of my devices (IPv4 and IPv6 only), the port is 0.

When would it be beneficial to associate an address and port to a device as one of its owned endpoints? The reason I ask is because I am developing a C# binding for libpcap and want to know if it would be useful or just erroneous/silly to expose all of the data from sockaddr_in to the user in the form of a System.Net.IPEndPoint property on my NetworkDeviceAddress class which describes the addresses owned by a particular device.

Answer 1

When would it be beneficial to associate an address and port to a device as one of its owned endpoints?

Rarely at best, and probably never. You're assuming that's why a sockaddr is used.

In fact, it's used as a way of supporting multiple address types; yes, a sockaddr might contain a port number, if it's AF_INET or AF_INET6, but, as the "if it's" clause suggests, it also contains an address family value.

libpcap/WinPcap is a cross-platform library, originally created for BSD UN*X, and created long before .NET even existed, so it was obviously not designed with .NET's networking objects in mind. (pcap_findalldevs() wasn't an API in the original libpcap, but it was added back in August-September 2001, which was before the final version of .NET 1.0 came out.)

The port number is not set to anything significant by pcap_findalldevs(), so there's no need to expose it in your wrapper.