Configuring IP TCP MSS

• Finding Feature Information, on page 1• Feature History for IP TCP MSS, on page 1• Information About IP TCP MSS, on page 2• Licensing Requirements for IP TCP MSS, on page 2• Default Settings for IP TCP MSS, on page 3• Guidelines and Limitations for IP TCP MSS, on page 3• Configuring IP TCP MSS, on page 3• Configuration Examples for IP TCP MSS, on page 4• Verifying IP TCP MSS, on page 5• Additional References for IP TCP MSS, on page 5

Finding Feature InformationYour software release might not support all the features documented in this module. For the latest caveatsand feature information, see the Bug Search Tool at https://tools.cisco.com/bugsearch/ and the release notesfor your software release. To find information about the features documented in this module, and to see a listof the releases in which each feature is supported, see the "New and Changed Information"chapter or theFeature History table in this chapter.

Feature History for IP TCP MSSTable 1: Feature History for IP TCP MSS

Feature InformationReleaseFeature Name

The IP TCP Maximum Segment Size (MSS)feature enables a switch to set a maximumsegment size for all the TCP connections thatoriginate from or terminate at a Cisco Nexus7000 Series Switch.

8.2(1)IP TCP MSS

Configuring IP TCP MSS1

Information About IP TCP MSSThe IP TCP Maximum Segment Size (MSS) feature enables a switch to set a maximum segment size for allTCP connections that originate or terminate at a Cisco Nexus 7000 Series switch. The MSS in a TCP headerfield is the maximum data size or payload that a host can send or receive in a single segment. By default, aCisco Nexus 7000 Series switch sets the MSS value to 536 bytes for IPv4 TCP connections and 1240 bytesfor IPv6 TCP connections. This default value is set by the switch during the initial TCP connectionestablishment.

The following figure shows how the MSS value is set between two switches for IPv4 TCP connections:

The ip tcp mss <2000> command is used on Host A to set the MSS to 2000 bytes. The difference betweenthe route interface MTU (1500 bytes) and the protocol header (40 bytes) is 1460 bytes.

For IPv6 TCP connections, the difference between the route interface MTU (1500 bytes) and the protocolheader (60 bytes) is 1440 bytes.

Note

The switch from which the TCP connection originates will always set the MSS to the user-configured MSSor the difference between the route interface MTU and the protocol header, whichever is lower. Thus, HostA sends a SYN packet with the proposed MSS of 1460 bytes to Host B. After receiving the SYN packet withthe proposed MSS, Host B sends a SYN-ACK packet to Host A, accepting the proposed MSS value for theTCP connection. Host A sends an ACK packet to Host B, setting theMSS value to 1460 for the TCP connection.

Licensing Requirements for IP TCP MSSIP TCP MSS requires no license. Any feature that is not included in a license package is bundled with theCisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of theCisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.

Configuring IP TCP MSS2

Configuring IP TCP MSSInformation About IP TCP MSS

Default Settings for IP TCP MSSDefault SettingParameter

536 bytes for IPv4 TCP connectionsIP TCP MSS

1240 bytes for IPv6 TCP connections

Guidelines and Limitations for IP TCP MSSIf the MSS has to be set to a value that is more than 1460 bytes for IPv4 TCP connections, the correspondingMTU value should be set to the required MSS value plus 40 bytes. If the MSS has to be set to a value that ismore than 1440 bytes for IPv6 TCP connections, the corresponding MTU value should be set to the requiredMSS value plus 60 bytes.

Configuring IP TCP MSS

Setting the MSS for TCP Connections

Procedure

Step 1 Enter global configuration mode:

switch# configure terminal

Step 2 Set a maximum segment size:

switch(config)# ip tcp mss <bytes>

The IP TCP MSS range is from 68 to 10000 bytes.Note

Step 3 (Optional) Display the configured IP TCP MSS:

switch# show ip tcp mss

Example: Running Configuration

This example shows a running configuration, followed by a verification command that displays theconfigured IP TCP MSS:

configure terminalip tcp mss 5000Setting TCP MSS to 5000 bytes

Configuring IP TCP MSS3

Configuring IP TCP MSSDefault Settings for IP TCP MSS

switch# show ip tcp mssTCP MSS value 5000 bytes

Removing a Set IP TCP MSS

Procedure

Step 1 Enter global configuration mode:

switch# configure terminal

Step 2 Remove the configured IP TCP MSS and set the IP TCP MSS to default values:

switch(config)# no ip tcp mss

Step 3 (Optional) Display the configured IP TCP MSS:

switch# show ip tcp mss

Example: Running Configuration

This example shows a running configuration, followed by a verification command that displays theconfigured IP TCP MSS:

configure terminalno ip tcp mss 5000Setting default MSS value is 536 bytes

switch# show ip tcp mssTCP MSS value 536 bytes

Configuration Examples for IP TCP MSS

Example: Setting the MSS for TCP Connections

configure terminalip tcp mss 2000

Example: Removing a Set IP TCP MSS

configure terminalno ip tcp mss

Configuring IP TCP MSS4

Configuring IP TCP MSSRemoving a Set IP TCP MSS

Verifying IP TCP MSSPurposeCommand

Displays the set IP TCP MSS.show ip tcp mss

Additional References for IP TCP MSSThis section describes additional information related to configuring IP TCP MSS.

Related Documents

Document TitleRelated Topic

Cisco NX-OS Licensing GuideCisco NX-OS licensingguide

Cisco Nexus 7000 Series NX-OS Interfaces Command ReferenceCommand reference

Configuring IP TCP MSS5

Configuring IP TCP MSSVerifying IP TCP MSS

Configuring IP TCP MSS6

Configuring IP TCP MSSAdditional References for IP TCP MSS