MSS - Maximum Segment Size

This Maximum Segment Size (MSS) announcement (often mistakenly called a negotiation) is sent from the data receiver to the data sender and says "I can accept TCP segments up to size X". The size (X) may be larger or smaller than the default.  
The MSS can be used completely independently in each direction of data flow.  The result may be quite different maximum
sizes in the two directions.

Below you can see an example where is saying he can accept a MSS of 1280 for all future TCP segments. And can only accept MSS`s of 1460 for all future TCP segments.   TCP   39884 > 22 [SYN] Seq=0 Len=0 MSS=1460 TSV=556758839    TCP   22 > 39884 [SYN, ACK] Seq=0 Ack=1 Win=16484 Len=0 MSS=1280 WS=0   TCP   39884 > 22 [ACK] Seq=1 Ack=1 Win=5888 Len=0

About the Author


R Donato

Rick Donato is the Founder and Chief Editor of He currently works as a Principal Network Security Engineer and has a keen interest in automation and the cloud.

You can find Rick on Twitter @f3lix001