Configuring 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.

For more information, see the Cisco Nexus 9000 Series NX-OS Interfaces Configuration Guide:

https://www.cisco.com/c/en/us/support/switches/nexus-9000-series-switches/products-installation-and-configuration-guides-list.html/

Configuring the Maximum Segment Size for TCP Connections in Bytes

Configuring the Maximum Segment Size for TCP Connections in Bytes

POST http://<mgmt0_IP>/api/mo/sys/tcpudp.json

{
  "tcpudpEntity": {
    "children": [
      {
        "tcpudpInst": {
          "attributes": {
            "tcpMssBytes": "4133"
}}}]}}

{
    imdata:[]
}

<System>
  <tcpudp-items>
    <inst-items>
      <tcpMssBytes>4133</tcpMssBytes>
    </inst-items>
  </tcpudp-items>
</System>

Note: This example was added in Release 9.3(1).

CLI Commands

The CLI commands are equivalent to the payload examples displayed in the pane on the right. Click the DME tab in the top-left corner of the right pane to view the JSON payload. Click the YANG tab to view the XML payload.

ip tcp mss 4133

Verifying a DME Configuration

The following table contains the distinguished name (DN) for each managed object (MO) in the DME payload. Issue a GET request using the DN to verify the configuration was posted or to get information about the configured properties of a particular object.

MO	DN
tcpudpEntity	sys/tcpudp
tcpudpInst	sys/tcpudp/inst

tcpudpInst Properties

The following table contains information about the tcpudpInst properties in the DME payload. For more information about the properties and MOs, see the NX-API DME Model Reference linked in the Related Documentation section below.

Property Name	Data Type	Description	Values
tcpMssBytes	tcpudp:TCPMss (scalar:Uint16)	Set the Tcp Mss Byte	RANGE: [88 , 10000] DEFAULT: 536

Related Documentation

For other CLI options, see the Cisco Nexus 9000 Series NX-OS Command Reference:

http://www.cisco.com/c/en/us/support/switches/nexus-9000-series-switches/products-command-reference-list.html

For detailed information about classes and attributes in the payload, see the NX-API DME Model Reference: https://developer.cisco.com/media/dme/index.html

For information about using the payloads, see the Cisco Nexus 9000 Series NX-OS Programmability Guide:

https://www.cisco.com/c/en/us/support/switches/nexus-9000-series-switches/products-programming-reference-guides-list.html

Deleting the Maximum Segment Size for TCP Connections in Bytes

Deleting the Maximum Segment Size for TCP Connections in Bytes

POST http://<mgmt0_IP>/api/mo/sys/tcpudp.json

{
  "tcpudpEntity": {
    "children": [
      {
        "tcpudpInst": {
          "attributes": {
            "tcpMssBytes": "536"
}}}]}}

{
    imdata:[]
}

<System>
  <tcpudp-items>
    <inst-items>
      <tcpMssBytes>536</tcpMssBytes>
    </inst-items>
  </tcpudp-items>
</System>