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

In the navigation pane, expand Configuration > IP.
Select IP.
Select the Globals tab.
Select TcpAdjustMssEnable to enable this functionality.
Optional: Enter a value in TcpAdjustMssValue.
Select Apply.

Globals Field Descriptions

Use the data in the following table to use the Globals tab.


Name	Description
Forwarding	Configures the system for forwarding (routing) or for dropping. The default value is forwarding.
DefaultTTL	Configures the default time-to-live (TTL) value for a routed packet. TTL indicates the maximum number of seconds elapsed before a packet is discarded. Enter an integer from 1 to 255. The default value of 255 is used if a value is not supplied in the datagram header.
ReasmTimeout	Specifies the maximum number of seconds that received fragments are held while they wait for reassembly. The default value is 30 seconds.
ICMPUnreachableMsgEnable	Enables the generation of Internet Control Message Protocol (ICMP) network unreachable messages if the destination network is not reachable from this system. These messages help determine if the system is reachable over the network. The default is disabled. Important: As a best pactice, enable icmp-unreach-msg only if it is absolutely required. If icmp-unreach-msg is enabled and a packet is received for which there is no route in the routing table, CPU utilization can dramatically increase.
ICMPRedirectMsgEnable	Enables or disables the system sending ICMP destination redirect messages.
IcmpEchoBroadcastRequestEnable	Enables or disables IP ICMP echo broadcast request feature. The default is enabled.
IcmpDropFragmentsEnable Note: Exception: Not supported on VSP 8600 Series and XA1400 Series.	Enables or disables IPv4 Fragmented ICMP packet filtering globally. The default is disabled.
AlternativeEnable	Globally enables or disables the Alternative Route feature. If the alternative-route parameter is disabled, all existing alternative routes are removed. After the parameter is enabled, all alternative routes are re-added. The default is enabled.
RouteDiscoveryEnable	Enables the ICMP Router Discovery feature. The default is disabled (not selected). Use ICMP Router Discovery to enable hosts attached to multicast or broadcast networks to discover the IP addresses of neighboring routers.
AllowMoreSpecificNonLocalRouteEnable	Enables or disables a more-specific nonlocal route. If enabled, the system can enter a more-specific nonlocal route into the routing table. The default is disabled.
SuperNetEnable	Enables or disables supernetting. If supernetting is globally enabled, the system can learn routes with a route mask less than 8 bits. Routes with a mask length less than 8 bits cannot have ECMP paths, even if you globally enable the ECMP feature. The default is disabled.
UdpCheckSumEnable	Enables or disables the UDP checksum calculation. The default is enable.
SourceRouteEnable	Enables or disables IP Source Routing globally. It is disabled by default.
ARPLifeTime	Specifies the lifetime of an ARP entry within the system, global to the switch. The default value is 360 minutes.
EcmpEnable	Globally enables or disables the Equal Cost Multipath (ECMP) feature. The default is disabled. After ECMP is disabled, the EcmpMaxPath is reset to the default value of 1.
EcmpMaxPath	Globally configures the maximum number of ECMP paths. You cannot configure this feature unless ECMP is enabled globally. Different hardware platforms can support a different number of ECMP paths. For more information, see VSP 8600 Release Notes.
Ecmp1PathList	Selects a preconfigured ECMP path.
Ecmp2PathList	Selects a preconfigured ECMP path.
Ecmp3PathList	Selects a preconfigured ECMP path.
Ecmp4PathList	Selects a preconfigured ECMP path.
Ecmp5PathList	Selects a preconfigured ECMP path.
Ecmp6PathList	Selects a preconfigured ECMP path.
Ecmp7PathList	Selects a preconfigured ECMP path.
Ecmp8PathList	Selects a preconfigured ECMP path.
EcmpPathListApply	Applies changes in the ECMP pathlist configuration, or in the prefix lists configured as the pathlists.
TcpAdjustMssEnable Note: Exception: Only supported on 5420 Series, 5520 Series, VSP 4900 Series, VSP 7400 Series, and XA1400 Series.	Adjusts the TCP maximum segment size (MSS) to improve the throughput for the TCP session over a Fabric Extend (FE) adjacency. The default varies depending on hardware platform: For XA1400 Series, the default value is enabled when at least one Fabric Extend (FE) tunnel with a MTU less than or equal to 1500 is configured. For VSP 4900 Series and VSP 7400 Series, the default is disabled.
TcpAdjustMssStatus Note: Exception: Only supported on 5420 Series, 5520 Series, VSP 4900 Series, VSP 7400 Series, and XA1400 Series.	Displays the activation status of the MSS adjustment functionality. On XA1400 Series, the MSS adjustment functionality only activates when at least one FE tunnel with a maximum transmission unit (MTU) less than or equal to 1500 is configured.
TcpAdjustMssType Note: Exception: Only supported on 5420 Series, 5520 Series, VSP 4900 Series, VSP 7400 Series, and XA1400 Series.	Displays if the MSS adjustment value is manually configured or auto-derived.
TcpAdjustMssValue Note: Exception: Only supported on 5420 Series, 5520 Series, VSP 4900 Series, VSP 7400 Series, and XA1400 Series.	Configures the MSS adjustment value. The default varies depending on hardware platform: For XA1400 Series, the default value is auto-derived. For VSP 4900 Series and VSP 7400 Series, the default value is 1300.