blocks|key|1280800|text|通常，这将取决于连接所使用的接口。您可能可以使用ioctl()来获取MTU，如果是以太网，则通常可以通过减去硬件报头的大小来获得最大数据包大小，对于没有VLAN的以太网，此大小为14。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1280801|只有当网络上的MTU至少有那么大时，才会出现这种情况。TCP可能会使用路径MTU发现来减少有效MTU。|1280802|问题是，你为什么要关心呢？|1280803|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

Generally, this will be dependent on the interface the connection is using. You can probably use an ioctl() to get the MTU, and if it is ethernet, you can usually get the maximum packet size by subtracting the size of the hardware header from that, which is 14 for ethernet with no VLAN.

This is only the case if the MTU is at least that large across the network. TCP may use path MTU discovery to reduce your effective MTU.

The question is, why do you care?

blocks|key|1066069|text|TCP+API中没有数据包。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1066070|在底层协议中经常有数据包，比如TCP是通过IP完成的，您对此并不感兴趣，因为它们与用户没有任何关系，除了您可能不感兴趣的非常微妙的性能优化(根据问题的公式)。|1066071|如果您问在一个API调用中可以send()的最大字节数是多少，那么这取决于实现和设置。您通常会调用send()来处理最多几千字节的数据块，并且总是准备好让系统拒绝全部或部分接受它，在这种情况下，您必须手动管理将数据分成更小的数据块，以便将数据提供给TCP+send()+API。|offset|length|style|CODE|1066072|entityMap^0|0|0|F|6|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|N|8|@$F|O|G|P|H|I]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

There're no packets in TCP API.

There're packets in underlying protocols often, like when TCP is done over IP, which you have no interest in, because they have nothing to do with the user except for very delicate performance optimizations which you are probably not interested in (according to the question's formulation).

If you ask what is a maximum number of bytes you can <code>send()</code> in one API call, then this is implementation and settings dependent. You would usually call send() for chunks of up to several kilobytes, and be always ready for the system to refuse to accept it totally or partially, in which case you will have to manually manage splitting into smaller chunks to feed your data into the TCP send() API.

blocks|key|1280906|text|在应用程序级别，应用程序使用TCP作为面向流的协议。TCP反过来又有分段，并抽象出处理不可靠IP数据包的细节。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1280907|TCP处理数据段而不是数据包。每个TCP数据段都有一个包含在TCP报头中的序列号。在TCP数据段中发送的实际数据是可变的。|1280908|在您可以使用的某些操作系统上，有一个名为TCP_MAXSEG的getsockopt值，它可以检索最大的TCP段大小(MSS)。不过，并不是所有操作系统都支持它。|offset|length|1280909|我不确定你到底想做什么，但是如果你想减少使用的缓冲区大小，你也可以看看:+SO_SNDBUF和SO_RCVBUF。|1280910|entityMap|0|LINK|mutability|MUTABLE|url|http://www.opengroup.org/onlinepubs/009695399/functions/getsockopt.html^0|0|0|V|A|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@$F|U|G|V|1|W]]|A|$]]|$1|H|3|I|5|6|7|X|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]]]

At the application level, the application uses TCP as a stream oriented protocol. TCP in turn has segments and abstracts away the details of working with unreliable IP packets. 

TCP deals with segments instead of packets. Each TCP segment has a sequence number which is contained inside a TCP header.
The actual data sent in a TCP segment is variable. 

There is a value for <a href="http://www.opengroup.org/onlinepubs/009695399/functions/getsockopt.html" rel="noreferrer">getsockopt</a> that is supported on some OS that you can use called TCP_MAXSEG which retrieves the maximum TCP segment size (MSS). It is not supported on all OS though.

I'm not sure exactly what you're trying to do but if you want to reduce the buffer size that's used you could also look into: SO_SNDBUF and SO_RCVBUF.

blocks|key|1066191|text|TCP包大小的绝对限制是64K+(65535字节)，但实际上这比你看到的任何包的大小都要大得多，因为较低的层(例如以太网)的包大小较小。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1066192|例如，用于以太网的MTU+(最大传输单元)是1500字节。某些类型的网络(如令牌环)具有较大的MTU，而某些类型具有较小的MTU，但这些值对于每种物理技术都是固定的。|1066193|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

The absolute limitation on TCP packet size is 64K (65535 bytes), but in practicality this is far larger than the size of any packet you will see, because the lower layers (e.g. ethernet) have lower packet sizes.

The MTU (Maximum Transmission Unit) for Ethernet, for instance, is 1500 bytes. Some types of networks (like Token Ring) have larger MTUs, and some types have smaller MTUs, but the values are fixed for each physical technology.

blocks|key|1281042|text|这是一个很好的问题，实际上我在工作中经常遇到这个问题。有很多“技术正确”的答案，比如65k和1500。我做了很多写网络接口的工作，使用65k是愚蠢的，1500也会给你带来大麻烦。我的工作在许多不同的硬件/平台/路由器上进行，老实说，我从1400字节开始。如果你需要超过1400，你可以开始一寸一寸地往上爬，你可能会到1450，有时到1480左右？如果你需要更多，那么你当然需要分成两个包，其中有几种明显的方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1281043|问题是，您正在讨论创建一个数据包并通过TCP将其写出，但当然还有附加的报头数据等等，所以您的“行李”会使您达到1500或更高。而且很多硬件都有较低的限制。|1281044|如果你“推动它”，你会得到一些非常奇怪的事情。显然是截断的数据，或者是我很少看到的丢弃的数据。损坏的数据也很少，但肯定会发生。|1281045|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

This is an excellent question and I run in to this a lot at work actually. There are a lot of "technically correct" answers such as 65k and 1500. I've done a lot of work writing network interfaces and using 65k is silly, and 1500 can also get you in to big trouble. My work goes on a lot of different hardware / platforms / routers, and to be honest the place I start is 1400 bytes. If you NEED more than 1400 you can start to inch your way up, you can probably go to 1450 and sometimes to 1480'ish? If you need more than that then of course you need to split in to 2 packets, of which there are several obvious ways of doing..

The problem is that you're talking about creating a data packet and writing it out via TCP, but of course there's header data tacked on and so forth, so you have "baggage" that puts you to 1500 or beyond.. and also a lot of hardware has lower limits.

If you "push it" you can get some really weird things going on. Truncated data, obviously, or dropped data I've seen rarely. Corrupted data also rarely but certainly does happen.

blocks|key|1066327|text|根据http://en.wikipedia.org/wiki/Maximum_segment_size的说法，网络中IPV4数据包的默认最大大小为536个八位字节(大小为8位的字节)。请参阅RFC+879|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1066328|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Maximum_segment_size|1|https://www.rfc-editor.org/rfc/rfc879#section-1^0|2|1D|0|2N|7|1|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]|$A|R|B|S|1|T]]|C|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]]]

According to <a href="http://en.wikipedia.org/wiki/Maximum_segment_size" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Maximum_segment_size</a>, the default largest size for a IPV4 packet on a network is 536 octets (bytes of size 8 bits). See <a href="https://www.rfc-editor.org/rfc/rfc879#section-1" rel="nofollow noreferrer">RFC 879</a>

blocks|key|1066387|text|如果您使用的是Linux机器，"ifconfig+mtu9000+up“是为接口设置eth0的命令。但是，我不得不说，如果网络传输不是那么稳定，那么大的MTU也有一些缺点，它可能会使用更多的内核空间内存。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1066388|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If you are with Linux machines, "ifconfig eth0 mtu 9000 up" is the command to set the MTU for an interface. However, I have to say, big MTU has some downsides if the network transmission is not so stable, and it may use more kernel space memories.

blocks|key|1281197|text|一种解决方案可以是将套接字选项TCP_MAXSEG+(http://linux.die.net/man/7/tcp)设置为对底层网络来说是“安全”的值(例如，为了在以太网上是安全的，设置为1400时)，然后在发送系统调用中使用大缓冲区。这样可以减少昂贵的系统调用。内核将拆分数据以匹配MSS。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1281198|通过这种方式，您可以避免截断数据，并且您的应用程序不必担心小缓冲区。|1281199|entityMap|0|LINK|mutability|MUTABLE|url|http://linux.die.net/man/7/tcp^0|R|U|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

One solution can be to set socket option TCP_MAXSEG (<a href="http://linux.die.net/man/7/tcp" rel="nofollow">http://linux.die.net/man/7/tcp</a>) to a value that is "safe" with underlying network (e.g. set to 1400 to be safe on ethernet) and then use a large buffer in send system call. 
This way there can be less system calls which are expensive. 
Kernel will split the data to match MSS. 

This way you can avoid truncated data and your application doesn't have to worry about small buffers.

blocks|key|1281265|text|似乎互联网上的大多数网站都使用1460字节作为MTU的值。有时候是1452，如果你在VPN上，IPSec报头会掉得更多。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1281266|默认窗口大小变化很大，最大可达65535字节。我使用http://tcpcheck.com查看我自己的源IP值，并检查其他互联网供应商正在使用什么。|offset|length|1281267|entityMap|0|LINK|mutability|MUTABLE|url|http://tcpcheck.com/^0|0|Q|J|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

It seems most web sites out on the internet use 1460 bytes for the value of MTU. Sometimes it's 1452 and if you are on a VPN it will drop even more for the IPSec headers.

The default window size varies quite a bit up to a max of 65535 bytes. I use <a href="http://tcpcheck.com" rel="nofollow">http://tcpcheck.com</a> to look at my own source IP values and to check what other Internet vendors are using.

blocks|key|1281300|text|IP协议(Ip4)中TCP设置的数据包大小。对于该字段(TL)，分配了16位，因此分组的最大大小为65535字节：IP+protocol+details|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1281301|entityMap|0|LINK|mutability|MUTABLE|url|https://i.stack.imgur.com/KGOoH.png^0|1L|J|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

The packet size for a TCP setting in IP protocol(Ip4). For this field(TL), 16 bits are allocated, accordingly the max size of packet is 65535 bytes: <a href="https://i.stack.imgur.com/KGOoH.png" rel="nofollow noreferrer">IP protocol details</a>

What is the maximum packet size for a TCP connection or how can I get the maximum packet size?

Maximum packet size for a TCP connection

大数据

路由器

路由

Linux

TCP连接的最大数据包大小是多少，或者如何获得最大数据包大小？

问TCP连接的最大数据包大小
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问TCP连接的最大数据包大小EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问TCP连接的最大数据包大小
EN