CODEWITHSUNDEEP
winapisocketstcpwinsockmss
Pavel Radzivilovsky
Pavel Radzivilovsky

Reputation: 19104

Setting MSS on per-socket basis with winsock?

As crazy as it sounds, there are situations in life when one needs to configure TCP stack parameters manually, such as MSS.

I see it can be done machine-wide as described, for example, here. But I need a way to configure it on per-tcp-socket basis.

Upvotes: 3

Views: 2195

Answers (3)

Jay Zhang
Jay Zhang

Reputation: 109

I think windows may does not allow you to adjust MSS per socket.

Here's the test sample:
Just call setsockopt with TCP_MAXSEG.
#include <ws2tcpip.h> 

`int mss = 512;`  
`setsockopt(sock, IPPROTO_TCP, TCP_MAXSEG, (char*)&mss, sizeof(mss);`

Set it before connect or listen.

I tested it with vs2015 on windows10. This code can pass the compile in VS2015, but can not run. Windows will give a error WSAENOPROTOOPT when it's running.

Upvotes: 0

Nikolai Fetissov
Nikolai Fetissov

Reputation: 84239

That should be standard setsockopt with TCP_MAXSEG. Just remember that this has to be done before connection is initiated (i.e. before connect or listen) and that TCP stack might change the actual value according to path MTU.

Upvotes: 2

jay.lee
jay.lee

Reputation: 19837

You can try calling setsockopt() with TCP_MAXSEG as is implied to be possible at the bottom of this MSDN article. But what's strange is that the TCP_MAXSEG is not a valid optname to supply to getsockopt(). So maybe it can be set but not retrieved? I guess give it a try and see if it works.

Upvotes: 0

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