所有的mtu都是一样的功能

【 在 freyoneby (freyoneby) 的大作中提到: 】
: 有什么标准描述这个的
: - 来自「最水木 for iPhone 7 Plus」
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FROM 60.186.219.*

是的，传输机制。　　（以前几条版面没显示，这是发的最后一条）

【 在 freyoneby (freyoneby) 的大作中提到: 】
: 收到的包大于MTU会丢弃？
: - 来自「最水木 for iPhone 7 Plus」
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FROM 115.193.175.*

大于ｍｔｕ就不得不分片传输，
械纳璞肝颂岣咝什幌敕制捎诓灰恢拢突岬贾隆。穑幔簦枭系纳璞溉衔飧霭螅Ω梅制吹模趺粗苯永戳耍投耍⑻崾景

ｒｆｃ７９１
The maximum sized datagram that can be transmitted through the
      next network is called the maximum transmission unit (MTU).

      If the total length is less than or equal the maximum transmission
      unit then submit this datagram to the next step in datagram
      processing; otherwise cut the datagram into two fragments, the
      first fragment being the maximum size, and the second fragment
      being the rest of the datagram.  The first fragment is submitted
      to the next step in datagram processing, while the second fragment
      is submitted to this procedure in case it is still too large.

ｒｆｃ１１９１
When one IP host has a large amount of data to send to another host,
   the data is transmitted as a series of IP datagrams.  It is usually
   preferable that these datagrams be of the largest size that does not
   require fragmentation anywhere along the path from the source to the
   destination.  (For the case against fragmentation, see [5].)  This
   datagram size is referred to as the Path MTU (PMTU), and it is equal
   to the minimum of the MTUs of each hop in the path.  A shortcoming of
   the current Internet protocol suite is the lack of a standard
   mechanism for a host to discover the PMTU of an arbitrary path.

The current practice [1] is to use the lesser of 576 and the
   first-hop MTU as the PMTU for any destination that is not connected
   to the same network or subnet as the source.  In many cases, this
   results in the use of smaller datagrams than necessary, because many
   paths have a PMTU greater than 576.  A host sending datagrams much
   smaller than the Path MTU allows is wasting Internet resources and
   probably getting suboptimal throughput.  Furthermore, current
   practice does not prevent fragmentation in all cases, since there are
   some paths whose PMTU is less than 576.

In this memo, we describe a technique for using the Don't Fragment
   (DF) bit in the IP header to dynamically discover the PMTU of a path.
   The basic idea is that a source host initially assumes that the PMTU
   of a path is the (known) MTU of its first hop, and sends all
   datagrams on that path with the DF bit set.  If any of the datagrams
   are too large to be forwarded without fragmentation by some router
   along the path, that router will discard them and return ICMP
   Destination Unreachable messages with a code meaning "fragmentation
   needed and DF set" [7].  Upon receipt of such a message (henceforth
   called a "Datagram Too Big" message), the source host reduces its
   assumed PMTU for the path.
【 在 freyoneby (freyoneby) 的大作中提到: 】
: 哪些标准有描述的
: - 来自「最水木 for iPhone 7 Plus」
--
FROM 115.193.175.*

居然还乱码了，对于发送方来说， 大于mtu值的包是必须分片传输的。   为了网络资源效率，有些设备会固定mtu的大小，当接收到大于mtu的包时，接收方就会返回，包太大，无法到达，估计就要求重新分片传输了
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FROM 220.191.249.*

哦，这个还真的没深究过


【 在 freyoneby (freyoneby) 的大作中提到: 】
: 从标准上理解接收方再转发这个包的时候，如果dp标志位不让分片，才会返回包太大
: - 来自「最水木 for iPhone 7 Plus」
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FROM 220.191.249.*