Information About IP TCP MSS
The IP TCP Maximum Segment Size (MSS) feature enables a switch to set a maximum segment size for all TCP connections that originate or terminate at a Cisco Nexus 9000 Series switch. The MSS in a TCP header field is the maximum data size or payload that a host can send or receive in a single segment. By default, a Cisco Nexus 9000 Series switch sets the MSS value to 536 bytes for IPv4 TCP connections and 1240 bytes for IPv6 TCP connections. This default value is set by the switch during the initial TCP connection establishment.
The switch from which the TCP connection originates will always set the MSS to the user-configured MSS or the difference between the route interface MTU and the protocol header, whichever is lower. Thus, Host A sends a SYN packet with the proposed MSS of 1460 bytes to Host B. After receiving the SYN packet with the proposed MSS, Host B sends a SYN-ACK packet to Host A, accepting the proposed MSS value for the TCP connection. Host A sends an ACK packet to Host B, setting the MSS value to 1460 for the TCP connection.