• Overview
• Symptoms
• Potential Root Cause
• Default MTU value
• Resolution Steps

Overview

Sometimes end users experience slow network performance or request time outs as a result of an MTU value that is too high for the underlying network path.

Symptoms

• Slow network performance
• Websites stalling or only partially loading

Potential Root Cause

The Maximum Transmission Unit (MTU) value set is too high for the network. This results in oversized packets getting fragmented or dropped, which causes latency or broken connections. Requests may only partly work or not work at all, depending on if the network can handle byte fragmentation.

Default MTU value

CSE sets the Service Tunnel MTU to 1280 by default, or to 1252 when Public IPs & Increased Connector Limit is turned on. These values leave room for the extra packet overhead that ISPs, site-to-site VPNs, and cloud provider networks such as Azure and AWS add, so most networks do not need a lower value. Before November 2026, the defaults were 1380 and 1352.

Desktop app versions before 4.8.0 still show “Default is 1380” under Settings > Preferences. That text is out of date. The tunnel uses the new default when it connects.

A value that a user enters under Settings > Preferences overrides the default. A device with its own value keeps that value after the default changes, so it does not get the new default. To move that device to the new default, set the value to 1280, or to 1252 when Public IPs & Increased Connector Limit is turned on.

Resolution Steps

1. Navigate from Settings > Preferences in the CSE desktop app, and adjust the MTU Value for your Service Tunnel. Note that the MTU Value entered must be between 1200-1380.

Note: Lowering the MTU Value will reduce throughput and can increase network latency.