The maximum segment size (MSS) is a parameter of the OPTIONS field of the TCP header that specifies the largest amount of data, specified in bytes, that a computer or communications device can receive in a single TCP segment. It does not count the TCP header or the IP header. The MSS limit applies to the total amount of data contained in the final, reconstructed TCP segment.
VulcanManager supports minimum TCP MSS of 70 bytes and maximum TCP MSS of 1460 bytes. Small MSS values results in higher protocol overhead. Each direction of data flow can use a different MSS.
Default TCP MSS is set to 1460 bytes on both directions. But you can modify it in Layer 4 - TCP -> Maximum TCP Segment Size as shown in the picture. If you want to change the TCP segment size sent by the server, you should change the MSS value of the client (red circle). If you want to change the TCP segment size sent by the client, you should change the MSS value of the server (blue circle). This is because the MSS value is used in the TCP header to advertise the the end how large segments it can receive.
There are three MSS Segment modifier types:
- Fixed. All TCP endpoints use the same MSS value.
- Increment. Each TCP endpoint uses a different MSS value in an increment order.
- Random. Each TCP endpoint uses a random MSS value in the range defined by a minimum and a maximum.