IPPROTO_IP(2const)

✨ IPPROTO_IP — the Linux IPv4 protocol socket options page (section 2const) ✨

okay bestie so this is IPPROTO_IP(2const) and it's literally your cheat-sheet page for the socket options that the IPv4 protocol layer keeps in its back pocket 💖 it's short, it's sweet, it's a table of contents with main character energy 👑

---

🌸 LIBRARY 🌸

Standard C library (libc, -lc) 🫶

---

🎀 SYNOPSIS 🎀

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

int setsockopt(int sockfd, IPPROTO_IP, int opt,
               const void val[size], size_t size);
int getsockopt(int sockfd, IPPROTO_IP, int opt,
               void val[size], size_t size);

---

💅 DESCRIPTION 💅

so IP lowkey has its own little collection of protocol-specific socket options, and you set them with setsockopt(2) and read them back with getsockopt(2), no cap. the socket option level you pass for all of these is IPPROTO_IP. periodt.

and here's every single one of them that's supported — each one has its own whole separate page, so this is basically the group chat roster and you go DM them individually 🌈:

• IP_ADD_MEMBERSHIP(2const)
• IP_ADD_SOURCE_MEMBERSHIP(2const)
• IP_BIND_ADDRESS_NO_PORT(2const)
• IP_BLOCK_SOURCE(2const)
• IP_DROP_MEMBERSHIP(2const)
• IP_DROP_SOURCE_MEMBERSHIP(2const)
• IP_FREEBIND(2const)
• IP_HDRINCL(2const)
• IP_LOCAL_PORT_RANGE(2const)
• IP_MSFILTER(2const)
• IP_MTU(2const)
• IP_MTU_DISCOVER(2const)
• IP_MULTICAST_ALL(2const)
• IP_MULTICAST_IF(2const)
• IP_MULTICAST_LOOP(2const)
• IP_MULTICAST_TTL(2const)
• IP_NODEFRAG(2const)
• IP_OPTIONS(2const)
• IP_PASSSEC(2const)
• IP_PKTINFO(2const)
• IP_RECVERR(2const)
• IP_RECVOPTS(2const)
• IP_RECVORIGDSTADDR(2const)
• IP_RECVTOS(2const)
• IP_RECVTTL(2const)
• IP_RETOPTS(2const)
• IP_ROUTER_ALERT(2const)
• IP_TOS(2const)
• IP_TRANSPARENT(2const)
• IP_TTL(2const)
• IP_UNBLOCK_SOURCE(2const)

thirty-one icons. we love to see it. 🌟

---

😭 ERRORS 😭

check setsockopt(2), and also check ip(7) — that's where the rest of the lore lives, bestie.

• ENOPROTOOPT — opt is invalid. that's it, that's the whole vibe, you passed something that isn't a real option 🙈

---

👑 HISTORY 👑

• IPPROTO_IP — POSIX.1-2001. literally an elder, been iconic since forever 💜

---

🦋 SEE ALSO 🦋

• setsockopt(2)
• ip(7)

---

and that's the page, bestie 🥰 this one's from Linux man-pages 6.20, dated 2026-01-05 — go forth and setsockopt responsibly, mwah 💋🎀