IP_MULTICAST_TTL(2const)

✨ IP_MULTICAST_TTL(2const) ✨

okay bestie so this is a <pink>Linux man-pages</pink> page, manual section <purple>2const</purple> (the const girlies — they live with IPPROTO_IP(2const)), all about the time-to-live value of outgoing multicast packets. 🦋

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💖 NAME 💖

IP_MULTICAST_TTL — the time-to-live value of your outgoing multicast packets, like the lil passport stamp that decides how far they're allowed to travel 🌍

📚 LIBRARY 📚

Standard C library (libc, -lc) — she's built in, no extra install, we love a low-maintenance queen 👑

🎀 SYNOPSIS 🎀

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

int setsockopt(int sockfd, IPPROTO_IP, IP_MULTICAST_TTL,
               const int *ttl, sizeof(int));
int getsockopt(int sockfd, IPPROTO_IP, IP_MULTICAST_TTL,
               int *ttl, sizeof(int));

so you can either set it or get it, and both of them take a pointer to an int called ttl — const int *ttl when you're writing, plain int *ttl when you're reading. literal perfection 💅

🌸 DESCRIPTION 🌸

Set or read the time-to-live value of outgoing multicast packets for this socket. That's the whole vibe. ✨

The default is 1, which means that multicast packets don't leave the local network unless the user program explicitly requests it. so by default your packets are homebodies — they stay in the local network and refuse to socialize outside unless you literally ask 🏠🙈

😭 ERRORS 😭

honestly she's not gonna spell it out here:

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

that's the group chat, go ask them 🫶

👑 HISTORY 👑

Linux 1.2. an icon from way back, she's been serving since forever ⭐

💀 CAVEATS 💀

It is very important for multicast packets to set the smallest TTL possible.

like, for real real. smallest TTL you can get away with. no cap. do not be out here yeeting your packets across the whole internet for no reason 🙅♀️🔥

🌈 SEE ALSO 🌈

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

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okay that's the whole page bestie, you ate 💖 big ups to Linux man-pages 6.20, dated 2025-11-25 — periodt, go set your TTL responsibly 🎀🦋✨