Will TCP handshake happen, if MSS is not the same on both sides?

 Yes, the TCP handshake can still occur even if the Maximum Segment Size (MSS) is not the same on both sides. The MSS is a TCP option that specifies the maximum amount of data that can be included in a single TCP segment. While it is common for both sides to negotiate and agree upon an MSS during the TCP handshake, it's not a strict requirement for the establishment of a TCP connection.

 

During the TCP handshake (the three-way handshake), the negotiation of various parameters, including the MSS, occurs in the SYN and SYN-ACK segments. Here's a simplified overview of the process:

 

1. **Client (SYN):**

   - The client sends a TCP segment with the SYN (synchronize) flag set.

   - The client may include the MSS option in the TCP options field of the SYN segment, indicating its preferred MSS.

 

2. **Server (SYN-ACK):**

   - The server responds with a TCP segment containing the SYN and ACK (acknowledge) flags set.

   - The server may include its preferred MSS in the TCP options field.

 

3. **Client (ACK):**

   - The client acknowledges the server's SYN by sending a TCP segment with the ACK flag set.

   - If the client did not include the MSS option in its SYN segment, it can use the MSS value received from the server.

 

While it's desirable for both sides to agree on a common MSS to optimize the use of network resources and prevent fragmentation, it's not mandatory for the MSS to be the same on both sides. The TCP stack on each side can adapt to different MSS values.

 

If the MSS values are different, the sending side is expected to adjust its segment sizes to match the agreed-upon MSS. This adaptation helps in preventing fragmentation and ensures efficient data transfer.

 

In practice, most TCP implementations are designed to handle variations in MSS values between the client and server, allowing for interoperability