Setting MSS for TCP Connections

MSS is used by TCP to define the maximum amount of data that a TCP interface can accept in any single packet (or segment size). The MSS value is typically negotiated during connection establishment and is not renegotiated.

By default, the router uses an MSS value of 536 bytes and the advertised MSS is derived from the MTU of the transmitting interface. However, you can use the tcp mss command to set the MSS for TCP advertisements.

tcp mss

• Use to specify the MSS value for TCP to advertise.

  Note: The MSS value is equal to the MTU value minus the IP and TCP headers, so the MSS value is generally 40 bytes less than the MTU.

• Use the vrfName variable to specify a VRF to which you want to assign the TCP MSS value.
• Example

  host1(config-if)#tcp mss 1000

• Use the no version to remove the MSS value so that the router uses the advertised MSS derived from the MTU of the output interface.
• See tcp mss

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