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LEDBAT with ConfigMgr = Pure Love? - By Daniel Olsson

Nov 19 2017

Here is a new post by guest blogger Daniel Olsson @danielolsson100 covering a quite exciting network feature in Windows 10 and Windows Server 2016. Please note that even though LEDBAT was announced already back in July 18, 2016 by the Windows Networking Team. You need to request assistance to enable LEDBAT from either Microsoft or a Microsoft Partner working with that team. That being said, take it away Daniel (and thanks). / Johan


So what is LEDBAT?
LEDBAT stands for Low Extra Delay Background Transport, and it is an algorithm that is used within the TCP stack in Windows 10 and Server 2016. The goal is to better utilize the available bandwidth on WAN/Internet traffic when it’s not used by anyone else.

Microsoft describes LEDBAT pretty good
"Windows LEDBAT is implemented as an experimental Windows TCP Congestion Control Module (CCM). Windows LEDBAT transfers data in the background and does not interfere with other TCP connections. LEDBAT does this by only consuming unused bandwidth. When LEDBAT detects increased latency that indicates other TCP connections are consuming bandwidth it reduces its own consumption to prevent interference. When the latency decreases again LEDBAT ramps up and consumes the unused bandwidth."


Why is it so interesting with ConfigMgr?

The short answer is content replication. LEDBAT works with standard DPs (TCP traffic, traditionally throttled by ConfigMgr Sender) and with BITS ( Background Intelligent Transfer Service) which ConfigMgr use to do content replication to Pull DPs.

So if you have a lot of DP:s worldwide then you can do the “old school traffic shaping” on the DP as before (see below), or you can configure it to use all available bandwidth, and put a more modern traffic shaper in place.


Old school traffic shaping in ConfigMgr.


When using LEDBAT, you simply don’t touch the ConfigMgr rate limits at all (see below), and let LEDBAT handling the control.


ConfigMgr rate limits configured for LEDBAT.


All you need to do, after enabling LEDBAT (again, not available publicly yet, you have to request assistance from either Microsoft or a Microsoft Partner working with that team). Is to run some PowerShell commands, so that the traffic from ConfigMgr site server to the DP is using LEDBAT instead.

# Define DataCenterCustom profile to use LEDBAT as congestionProvider
# This is TAP code for now, you need to request to test LEDBAT from Microsoft/Partner
Set-NetTCPSetting -SettingName "DataCenterCustom" -CongestionProvider LEDBAT

# Set the LEDBAT filter to only apply for specific DP:s
New-NetTransportFilter –SettingName DatacenterCustom –DestinationPrefix
New-NetTransportFilter –SettingName DatacenterCustom –DestinationPrefix

If you have one ConfigMgr server/DP and the rest of the devices are over WAN ? Then apply one PowerShell line to run all traffic within the LEDBAT TCP flow

New-NetTransportFilter –SettingName DatacenterCustom –DestinationPrefix 


Finally, transport filter does not apply to existing traffic so do a reboot on the ConfigMgr site server.


Notes from the real world (enterprise customer test, large retail chain) 
The LEDBAT algorithm seems to work best in traditional  WAN scenarios, we got some great results for the ConfigMgr to remote DPs traffic. We are still investigating it’s behavior in LAN areas with very low latency (close to 0), where it did not behave very well. This will hopefully be fixed in the final release, in one of the upcoming versions of the windows Server 2016 operating system.

Also note that if you implement LEDBAT in networks when the WAN links are already fully used, meaning when you have like 0 kb bandwidth available …well... Then the LEDBAT TCP traffic will politely wait until there is free bandwidth available, and that might take a very long time:)


In the best of worlds
Add LEDBAT / BranchCache to your ConfigMgr environment, where it’s applicable, to use more bandwidth without interfering with normal TCP traffic


Need to learn more?

LEDBAT announcement:

Microsoft Ignite 2017 session by Andreas Hammarskjöld @andhammarskjold and Daniel Havey (Microsoft) , BRK3056: > This is a must see session!


That’s all for me, thanks for reading



Daniel Olsson

I do consulting in the ConfigMgr / EM+S field for
You can reach or follow me on twitter @danielolsson100.

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