Netscaler Knowledgebase

Summary

This document describes how to change the Maximum Transmission Unit (MTU) size to 1300.

Requirements

• Access to shell with root privileges

• Change should be made during a low period of NetScaler activity

• Adjacent routers and servers should have similar network changes made

Background

Refer to the following links for background information:

http://www.webopedia.com/TERM/M/MSS.html

http://www.webopedia.com/TERM/M/MTU.html

MTU of 1514 = TCP MSS of 1460 (Difference = 54 bytes)
MTU of 1300 = TCP MSS of 1246

This applies to TCP MSS, and does not apply to MTU for all other types of Ethernet frames.

Procedure

1. Execute the following command from the shell:

# nsapimgr -ys ns_max_mss=1300

(1460 is the default value for the MSS used by NetScaler.)

2. Save this command in rc.netscaler.

A better approach would be to allow the NetScaler to auto discover the MTU size by using the PMTUD command. At the shell prompt enter:

> enable ns mode pmtud
Path MTU Discovery enabled.
Done

The NetScaler uses Internet Control Message Protocol (ICMP) messages to auto discover the best MTU size.