From e0b344f3c8210e07bd75ba7f6d8f22a8f01570d3 Mon Sep 17 00:00:00 2001
From: Sergey Matveev <stargrave@stargrave.org>
Date: Sat, 24 Feb 2024 23:55:14 +0300
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ÐÑÐ¸ Ð¸ÑÐ¿Ð¾Ð»ÑÐ·Ð¾Ð²Ð°Ð½Ð¸Ð¸ gif/gre/stf ÑÑÐ½Ð½ÐµÐ»ÐµÐ¹ Ð² FreeBSD, Ð¾ÑÐ¿ÑÐ°Ð²Ð»ÑÐµÐ¼ÑÐµ Ð¿Ð°ÐºÐµÑÑ
ÑÐ¾ÑÑÐ¸ÑÐ¾Ð²Ð°Ð½Ð½Ð¾ ÑÑÐ°Ð³Ð¼ÐµÐ½ÑÐ¸ÑÑÑÑÑÑ ÐµÑÐ»Ð¸ ÑÐ°Ð·Ð¼ÐµÑÐ¾Ð¼ Ð±Ð¾Ð»ÑÑÐµ Ð¼Ð¸Ð½Ð¸Ð¼Ð°Ð»ÑÐ½Ð¾Ð³Ð¾ MTU IPv6
(1280 Ð±Ð°Ð¹Ñ). sys/netinet6/in6_gif.c:

    [...]
    /*
     * force fragmentation to minimum MTU, to avoid path MTU discovery.
     * it is too painful to ask for resend of inner packet, to achieve
     * path MTU discovery for encapsulated packets.
     */
    return (ip6_output(m, 0, NULL, IPV6_MINMTU, 0, NULL, NULL));

Ð¢Ð°Ðº ÐºÐ°Ðº Ñ Ð¼ÐµÐ½Ñ gif-ÑÑÐ½Ð½ÐµÐ»Ñ Ð¸ÑÐ¿Ð¾Ð»ÑÐ·ÑÐµÑÑÑ Ð´Ð»Ñ Ð¸Ð½ÐºÐ°Ð¿ÑÑÐ»ÑÑÐ¸Ð¸ IPv4 ÑÑÐ°ÑÐ¸ÐºÐ°
Ð¿Ð¾Ð²ÐµÑÑ Ð´Ð¸Ð½Ð°Ð¼Ð¸ÑÐµÑÐºÐ¸ Ð¼Ð°ÑÑÑÑÑÐ¸Ð·Ð¸ÑÑÐµÐ¼Ð¾Ð³Ð¾ IPv6, ÐºÐ¾ÑÐ¾ÑÑÐ¹ Ð¿Ð¾Ð²ÐµÑÑ ÑÐ»Ð¾Ð½Ð¾ÐºÐ°Ð´ÑÐ¾Ð²
Ð¸Ð´ÑÑ, Ð° MTU gif-ÑÑÐ½Ð½ÐµÐ»Ñ = 1500, ÑÐ¾ ÐºÑÑÐ° Ð¿Ð°ÐºÐµÑÐ¾Ð² ÑÑÐ°Ð³Ð¼ÐµÐ½ÑÐ¸ÑÑÐµÑÑÑ Ð±ÐµÐ·
ÐºÐ°ÐºÐ¾Ð¹-Ð»Ð¸Ð±Ð¾ Ð½ÐµÐ¾Ð±ÑÐ¾Ð´Ð¸Ð¼Ð¾ÑÑÐ¸. ÐÑÑ Ð¶Ðµ Ð½Ð° Ð¿ÑÑÑÐ¾Ð¼ Ð¼ÐµÑÑÐµ ÑÑÑÑ Ð»Ð¸ Ð½Ðµ ÑÐ´Ð²Ð°Ð¸Ð²Ð°ÑÑ
ÐºÐ¾Ð»Ð¸ÑÐµÑÑÐ²Ð¾ Ð¿Ð°ÐºÐµÑÐ¾Ð² Ð½Ðµ Ð¾ÑÐµÐ½Ñ Ð¿ÑÐ¸ÑÑÐ½Ð¾, Ð¿Ð¾ÑÑÐ¾Ð¼Ñ Ð¼Ð¾Ð¶Ð½Ð¾ Ð¿ÑÐ¾ÑÑÐ¾ Ð¿Ð¾Ð¼ÐµÐ½ÑÑÑ ÑÑÐ¾Ñ
IPV6_MINMTU Ð½Ð° Ð½Ð¾Ð»Ñ.
-- 
2.44.0