IPPROTO_IP(2const)

✨ IPPROTO_IP(2const) ✨

okay bestie, gather round, because this is a 2const page from the Linux man-pages (version 6.20, dated 2025-11-25, mwah 💖) and it's short but it is so important, no cap.

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🎀 NAME 🎀

IPPROTO_IP — include a user-supplied IP header 💌

Like, you're the main character and you're writing the IP header yourself. Iconic behaviour, honestly.

📚 LIBRARY 📚

Standard C library (libc, -lc). The classic. The blueprint. Periodt.

🌸 SYNOPSIS 🌸

#include <netinet/in.h>  /* Definition of IP* constants */
#include <sys/socket.h>

int setsockopt(int sockfd, IPPROTO_IP, IP_HDRINCL,
               const int *enable, sizeof(int));

💅 DESCRIPTION 💅

So here's the vibe: if this gets enabled, the user supplies an IP header in front of the user data. You're not letting the kernel do the header thing for you — you're doing it yourself, and honestly? slay.

Heads up bestie, this is valid only for SOCK_RAW sockets. That's not optional, that's the rules. Go peek at raw(7) for more info on that whole situation. 🦋

And here's the part you need to know, because it will lowkey ruin your day otherwise: when this flag is enabled, the values set by IP_OPTIONS(2const), IP_TTL(2const), and IP_TOS(2const) are ignored. Just — fully ignored. Not merged, not consulted, not even a little. You set them, the kernel looks away, the header is yours. 🫶

💀 ERRORS 💀

Not gonna reinvent the wheel here:

• See IPPROTO_IP(2const).
• See setsockopt(2).
• See ip(7).

🕰️ HISTORY 🕰️

Linux 2.0. Ancient. Elder emo of socket options, fr fr. 🔥

👀 SEE ALSO 👀

• IPPROTO_IP(2const)
• setsockopt(2)
• ip(7)

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and that's the whole page, bestie — short, sweet, and absolutely carrying your raw sockets on its back 👑

Linux man-pages 6.20 · 2025-11-25 — mwah, go forth and build your own headers 💖✨