topic Re: TCP MSS in General Topics

TCP MSS

zwaza — Mon, 15 Sep 2025 14:53:52 GMT

Below is the statement on MSS from PALO ALTO KB:

The TCP MSS, the maximum segment size, 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 include the TCP header (20bytes) or the IP header (20bytes).
This MSS value is announced (often mistakenly called a negotiation) from both sides during the TCP 3WHS.

Each side says: I can accept TCP segments up to the size of x.

Once each side announces its MSS, the remote side is expected to send packets containing a TCP segment no larger than the announced MSS value.

Now my query based on above statement is if one side has announced its MSS as 1400 BYTES and other side has sent TCP segment with 1450 BYTES of size.
Will the other side processes the segment or simply drops it?

Re: TCP MSS

Raido_Rattameister — Mon, 15 Sep 2025 16:46:57 GMT

Endpoints share maximum MSS in initial TCP 3way handshake.

Why would one participant send to packet to second participant with bigger payload than second participant notified in the beginning of communication?

Smaller MSS is usually advertised to avoid packet fragmentation by routers/firewalls on the path and not due endpoint's capability to accept full size packet.

Re: TCP MSS

zwaza — Tue, 16 Sep 2025 12:55:34 GMT

Why would one participant send to packet to second participant with bigger payload than second participant notified in the beginning of communication?

From the above questionaries You mean to say that there is no chance that TCP host can send higher TCP segments in size to other TCP host announced in initial 3 way handshake?
If "NO" then what would be the action of other TCP host on that segment, will it drop it or process?