tcp adjust-mss inbound

Function

The tcp adjust-mss inbound command sets the maximum segment size (MSS) for received TCP SYN/SYN+ACK packets.

The undo tcp adjust-mss inbound command cancels the configuration.

By default, no MSS is set for received TCP SYN/SYN+ACK packets.

Format

tcp adjust-mss mss-value inbound

undo tcp adjust-mss mss-value inbound

Parameters

Parameter	Description	Value
mss-value	Specifies the MSS for received TCP SYN/SYN+ACK packets.	The value is an integer ranging from 32 to 9500, in bytes.

Parameter

Description

Value

mss-value

Specifies the MSS for received TCP SYN/SYN+ACK packets.

The value is an integer ranging from 32 to 9500, in bytes.

Views

Eth-Trunk sub-interface view, Eth-Trunk interface view, Eth-Trunk interface view, GE sub-interface view, GE interface view, VBDIF interface view, VLANIF interface view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
ethernet	write

Usage Guidelines

Usage Scenario

After a user device and carrier device negotiate an MSS value in TCP packets and set up a TCP connection, the intermediate device forwards TCP packets between the two ends. The device may encapsulate additional headers into the TCP packets to be forwarded. If the packet length exceeds the negotiated MSS after the additional headers are encapsulated, the TCP packets are fragmented, deteriorating the transmission efficiency. To prevent this issue, run the tcp adjust-mss inbound command on the device. The device will then compare the MSS in received SYN/SYN+ACK packets with the one specified using the command. If the MSS specified in the command is smaller, the device changes the MSS to the specified value before forwarding the TCP packets. Otherwise, the device does not change the MSS in the packets.

Precautions

The command configuration is effective only for TCP SYN/SYN+ACK packets in IPv4 unicast scenarios and TCP SYN/SYN+ACK packets on the public network side in L3VPN scenarios.

Before running this command on a sub-interface, ensure that the sub-interface is configured with one of the following encapsulation modes:

Run the vlan-type dot1q command to configure dot1q VLAN encapsulation.
Run the dot1q termination vid command to configure dot1q VLAN termination.
Run the qinq termination ce-vid command to configure QinQ VLAN termination.
Run the vlan-type dot1q 8021p command to configure dot1q VLAN encapsulation to implement flexible service access.
Run the dot1q termination vid 8021p command to configure dot1q VLAN termination to implement flexible service access.

If the tcp adjust-mss inbound command is run more than once on the same interface, the latest configuration overrides the previous one.

Example

# Set the MSS to 1450 bytes for the TCP SYN/SYN+ACK packets received by GE0/1/8.1.

<HUAWEI> system-view
[~HUAWEI] interface GigabitEthernet 0/1/8.1
[~HUAWEI-GigabiteEhernet0/2/0.1] tcp adjust-mss 1450 inbound