IPV6_MTU(2const)

💖 IPV6_MTU — like, the whole vibe 💖

okay bestie, pull up a chair, we're reading IPV6_MTU(2const) together and it's gonna be so good, i promise 🫶

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🌸 NAME 🌸

IPV6_MTU — path maximum transmission unit size

like... it's the MTU. for the path. that's the whole thing. slay.

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🎀 LIBRARY 🎀

Standard C library (libc, -lc) — yes girl, the regular one, nothing fancy ✨

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🦋 SYNOPSIS 🦋

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

int setsockopt(int sockfd, IPPROTO_IPV6, IPV6_MTU,
               const int *val, sizeof(int));
int getsockopt(int sockfd, IPPROTO_IPV6, IPV6_MTU,
               int *val, sizeof(int));

not me including the exact headers word for word, because i respect you 💅

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🌈 DESCRIPTION 🌈

so there's two ways to talk to this option and they are giving totally different energy:

✨ getsockopt() ✨

Retrieve the current known path MTU of the current socket, bestie. That's it, that's the tea.

⚠️ Valid only when the socket has been connected. Not connected? Not valid. No cap. 😭

✨ setsockopt() ✨

Set the MTU to be used for the socket. The MTU is limited by the device MTU or the path MTU when path MTU discovery is enabled.

so like, you can ask for a number, but the device MTU and the path MTU (if path MTU discovery is on) are the ones actually holding the leash 🧚 it's giving "you don't get to pick, the network picks for you" fr fr.

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💀 ERRORS 💀

See IPPROTO_IPV6(2const). See setsockopt(2). See ipv6(7).

(translation: the drama lives in those pages, go read them, i'm not repeating it 🍓)

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👑 SEE ALSO 👑

• IPPROTO_IPV6(2const)
• setsockopt(2)
• ipv6(7)

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and that's the whole page, you ate it, i'm so proud of you 💜

source + version tea: this is from Linux man-pages 6.20, dated 2025-12-02. periodt. 💅✨