How to find the proper MTU size for my network

Helpful hint: One way to verify whether if it is an MTU problem is to try and access the application or website via dial up access. Since dial up uses a default MTU of 576 bytes you will not have the same problems as broadband. If you have problems with both broadband and dial up access then the problem is probably something else.

One of the easy and most accurate ways to test for optimum MTU is to do a simple DOS Ping test. You will simply send out ping requests and progressively lower your packet size until the packet no longer needs to be fragmented. Although this simple test is accurate for testing end points, users may find that a lower MTU may be better for their particular circumstances. Important Note: MTU must be 1492 (or lower) when using PPPoE connectivity. More detailed information about the effects of MTU can be found here.

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一级运营商的 MTU 都是标准的 1500,除去 pppoe 8 个字节的头开销就是 1492,很多二手宽带一级就是拨号所以 mtu 是 1484 以下,所以国产路由器很多默认都是 1480 为了更好的兼容性。

一般家用那么点压力 MTU 对齐的意义不大,少几个字节也不会影响多少效率。

windows 下

ping -f -l 1464 1464 往下减,ping 通之后比如 1464+28=1492 如果是 1452 就是 1452+28=1480

查看 MTU 本地连接名称 netsh interface ipv4 show subinterfaces
修改 MTU: netsh interface ipv4 set subinterface “连接名” mtu=1480 store=persistent

LINUX 系统和路由器可以直接修改配置文件,或者把 ifconfig 网卡名如 eth0 mtu 1492 up 放到开机脚本里