Tip of the Day: Let's Talk About LEDBAT

Today’s Tip… Let’s Talk About LEDBAT

You may have seen tips on this subject in the past, but let’s see where we are at today!

To Begin With, What is LEDBAT?

LEDBAT (Low Extra Delay Background Transfer) is a latency optimized, network congestion control provider. As a scavenger protocol, it is designed to automatically yield bandwidth to users and applications, while consuming any available bandwidth for background transfers when the network is not in use.

• When increased latency is detected (indicating that other TCP connections are consuming bandwidth) it reduces its own consumption to prevent interference.
• When latency decreases LEDBAT ramps up, consuming the unused bandwidth.

In other words, you can transfer SCCM Packages or Microsoft Updates without interfering with critical application traffic.

Things To Remember About LEDBAT

Use Cases

• LEDBAT can be enabled on a SCCM distribution point running Windows Server 2019.
• LEDBAT can be configured for WSUS servers using NetTransportFilters (see more below)
• BITS is also using LEDBAT for background uploads.
• Current Insider Preview builds have added support for use of LEDBAT by Delivery Optimization.

Configuration Notes

• LEDBAT can optimize any TCP sender-side workload.  It is not limited to updates!
• Congestion providers are configured per-flow:
  • LEDBAT provides congestion control for background traffic flows.
  • It does not compete with or replace congestion providers such as CUBIC, which are used for foreground traffic flows.
• Configure LEDBAT using the Internet Custom template. Never enable LEDBAT using the DataCenter template.
  • This is a common configuration error that can cause LEDBAT to get stuck in slow-transfer-mode, preventing it from ramping up to leverage unused bandwidth.
  • For more on this issue and how to properly configure LEDBAT, see Support for LEDBAT: Public Service Announcement
  • Transport Filters can seem somewhat mystical until you dive in and see how simple they really are.
    Advanced Users, see TCP Templates for Windows Server 2019 – How to tune your Windows Server Transports for an easy to understand explanation.
• LEDBAT has been backported to Windows Server 2016 (kb4132216,4284833)