IP_RECVTTL(2const)

✨ IP_RECVTTL(2const) ✨

okay bestie, so this one lives in the (2const) girlies section of the Linux man-pages, and it's all about flagging — literally, it's a socket option constant 🎀

---

💫 NAME 💫

IP_RECVTTL — the flag that says "yes queen, enable that IP_TTL control message" 👑

---

📚 LIBRARY 📚

Standard C library (libc, -lc) — the usual girlies, nothing new here, she's standard for a reason 🫶

---

🌸 SYNOPSIS 🌸

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

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

look at that #include <netinet/in.h> up top — that's where all the IP* constants live, iykyk 💅

---

💖 DESCRIPTION 💖

so when this flag is set (yes, set, not unset — we're turning things ON around here), the kernel will pass a IP_TTL(2const) control message your way, carrying the time-to-live field of the received packet as a 32 bit integer ✨

bestie warning 🚨 — this is not supported for SOCK_STREAM sockets. if you're on a stream socket, she simply will not serve. sorry babe 💀

---

🦋 ERRORS 🦋

like, go read the OGs:

• IPPROTO_IP(2const) — for the protocol-level tea
• setsockopt(2) — for the socket-option tea
• ip(7) — for the IP-layer tea 🍓

---

🔥 VERSIONS 🔥

okay this is the important plot twist so listen up diva: some BSD sockets implementations also provide an IP_RECVTTL option, BUT over there an ancillary message with type IP_RECVTTL gets passed along with the incoming packet 😭

that is different from the IP_TTL(2const) option used in Linux — so if you port code across and it's giving weird vibes, that's why. no cap 💅

---

📜 HISTORY 📜

Linux 2.2 — she's vintage, she's iconic, she's been here since 2.2 🌈⭐

---

👀 SEE ALSO 👀

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

---

and that's the whole page, bestie 🎀 this little icon came straight out of Linux man-pages 6.20, dated 2025-11-25 — go slay some sockets with your TTL values, mwah 💖👑🦋