networking protocol_error ai_generated partial

IPv6：到目标2001:db8::1的路径MTU发现失败，数据包大小1280

IPv6: Path MTU Discovery failed for destination 2001:db8::1, packet size 1280

ID: networking/ipv6-mtu-path-discovery-failure

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85%修复率
82%置信度
1证据数
2024-06-10首次发现

版本兼容性

版本状态引入弃用备注
Linux 5.15+ active — — —
FreeBSD 13.2 active — — —
Cisco IOS 15.0 active — — —
Juniper Junos 21.0 active — — —

根因分析

中间路由器丢弃了路径MTU发现所需的ICMPv6数据包过大消息（类型2），导致发送方假设更大的MTU，从而导致数据包丢弃或分片失败。

English

An intermediate router is dropping ICMPv6 Packet Too Big messages (type 2) required for Path MTU Discovery, causing the sender to assume a larger MTU and leading to packet drop or fragmentation failure.

generic

官方文档

https://datatracker.ietf.org/doc/html/rfc8201

解决方案

  1. Set the minimum MTU for the route to 1280 bytes to bypass PMTUD: ip route add 2001:db8::1/128 via fe80::1 dev eth0 mtu 1280
  2. Enable ICMPv6 filtering rules on intermediate routers to allow ICMPv6 type 2 messages (packet too big) through the firewall

无效尝试

常见但无效的做法:

  1. 95% 失败

    This disables IPv6 connectivity completely, which may break applications that require IPv6 and is not a targeted fix.

  2. 80% 失败

    The issue is on the path, not the sender; a static MTU does not address the router dropping ICMPv6 messages.