# ip tcp adjust-mss

#### Syntax

[ ip ] tcp adjust-mss mssAdjustment

no [ ip ] tcp adjust-mss

#### Release Information

Command introduced before JunosE Release 7.1.0.

#### Description

Modifies the maximum segment size (MSS) for TCP SYN packets traveling through the interface. The router compares the MSS value of incoming or outgoing packets against the MSS adjustment value. For any packet that contains an MSS value larger than the MSS adjustment value, the router replaces the MSS option with the configured adjustment value. If the packet does not contain an MSS value, the router assumes a value of 536 for the packet MSS on which to base the comparison. The no version removes the MSS modification.

| Note: The purpose behind using MSS is to alleviate problems with Path MTU Discovery (PMTUD) and resulting “ black hole” detection issues. See RFC 2923—TCP Problems with Path MTU Discovery (September 2000) for additional information about the black hole scenario.

#### Options

- ip—Specifies optional keyword for use with older scripts
- mssAdjustment—Adjustment value for the MSS; in the range 160–10240

#### Mode

Interface Configuration, Profile Configuration