Adjust the TCP Maximum Segment Size

Note

This procedure only applies to 5420 Series, 5520 Series, VSP 4900 Series, VSP 7400 Series, and XA1400 Series.

Adjust the TCP maximum segment size (MSS) to improve the throughput for the TCP session over a Fabric Extend (FE) adjacency.

About this task

Note

If you downgrade to an earlier release that does not support this feature, you must disable the feature and save the configuration. Downgrading to an earlier release requires a compatible configuration file.

The default varies depending on hardware platform:

For XA1400 Series, this functionality is enabled when at least one Fabric Extend (FE) tunnel with a MTU less than or equal to 1500 is configured, and the value is auto-derived.
For VSP 4900 Series, VSP 7400 Series, 5420 Series, and 5520 Series, this functionality is disabled. The default value, when enabled, is 1300.

Procedure

Enter Global Configuration mode:

enable

configure terminal
Use one of the following commands to configure the MSS adjustment functionality as required:
1. Configure an explicit MSS adjust value:
  
  ip tcp adjust-mss <max-segment-size> [enable]
2. Disable MSS adjustment explicitly:
  
  no ip tcp adjust-mss enable
3. Disable a configured MSS adjustment value and return to the auto-derived value:
  
  Note
  
  This step only applies to XA1400 Series.
  
  no ip tcp adjust-mss enable
Verify the configuration:

show ip tcp adjust-mss

Examples

Configure an MSS value of 1100 and verify the configuration.

Switch:1>enable
Switch:1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch:1(config)#ip tcp adjust-mss 1200

Switch:1>show ip tcp adjust-mss
================================================================================
                              IP TCP Adjust MSS
================================================================================
ENABLE            STATUS            TCP MSS                   TCP MSS
                                    TYPE                      VALUE
--------------------------------------------------------------------------------
TRUE              ACTIVE            MANUAL-CONFIG             1200

Disable the configured MSS adjustment value on XA1400 Series and verify the configuration:

Switch:1>enable
Switch:1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch:1(config)#no ip tcp adjust-mss enable
Switch:1(config)#show ip tcp adjust-mss
================================================================================
                          IP TCP Adjust MSS
================================================================================
ENABLE      STATUS       TCP MSS         TCP MSS
                         TYPE            VALUE
--------------------------------------------------------------------------------
TRUE        ACTIVE      AUTO-DERIVED     1300