ip tcp-mtu-probing

Enables Transmission Control Protocol (TCP) maximum transmission unit (MTU) probing so that a working path MTU can be discovered without relying on Internet Control Message Protocol (ICMP) messages.
Syntax
ip tcp-mtu-probing { disable | enable }
no ip tcp-mtu-probing disable
Command Default

TCP MTU probing is enabled by default.

Parameters
disable
Disables TCP MTU probing.
enable
Enables TCP MTU probing if it has been disabled.
Modes

Global configuration mode

Usage Guidelines

TCP MTU probing allows the system to discover a working path MTU without relying on ICMP messages. When this feature is enabled, the system automatically adjusts the TCP Maximum Segment Size (MSS) if acknowledgments are not received due to oversized segments.

This behavior helps prevent TCP blackholing and throughput degradation when traffic traverses tunnels such as GRE, IPsec, or VXLAN, where the effective path MTU may be smaller than the interface MTU.

Both ip tcp-mtu-probing enable and no ip tcp-mtu-probing disable result in TCP MTU probing being enabled. Use ip tcp-mtu-probing enable to explicitly set the feature in the running configuration. Use no ip tcp-mtu-probing disable to remove a previous disable configuration and revert to the default enabled state.

The no form of the command removes the disable configuration and restores the default behavior, with TCP MTU probing enabled.

Examples

The following example disables TCP MTU probing. 

device# configure terminal
device(config)# ip tcp-mtu-probing disable

The following example re-enables TCP MTU probing if it has been disabled. 

device# configure terminal
device(config)# ip tcp-mtu-probing enable
History
Release version Command history
10.0.10g_cd7, 10.0.10h05 This command was introduced.
Parent topic: Commands I