What is Large Send Offload?
As you might be aware that standard TCP packet consists of 1500 bytes (1 Frame = 1500 bytes) of data for the MTU (Maximum Transmission Unit) of 1500 bytes. Jumbo frame supports TCP packets of 1500-9000 bytes in a single frame as per the MTU setup for jumbo frame (1500-9000 bytes), however while setting up jumbo frames all the network devices must support jumbo frames and MTU setup for jumbo frames must be same for all devices.
Large send offload allows TCP layer to build 64KB of data in a single frame i.e. it allows MTU of 64KB. To send 64KB of data with MTU of 1500 bytes, TCP layer needs to compose approximately 44 segments which needs more host processing which results in more host CPU utilization. So, with Large Send Offload reduces host processing and hence less host CPU utilization. However Large Send Offload results low raw throughput down the wire. Below are the issues those I have faced due to Large Send Offload enabled by default on the Network Adapter on our newly purchased Windows 7 Professional Systems.
Issue List
- Copying data files very slow on a network share (LAN). Data transfer rate is less than 18KBps over 1Gbps LAN connection.
- Spooling documents to print queue very slowly on a shared Printer. Print spooler very slow. To spool a document say 1 MB to a print queue on a shared printer is taking hours and due to this print given by other users to the same printer are stuck up in the queue.
- Issue were observed on newly bought System with the Configuration as given below.
System Configuration
Operating System
- Windows 7 Professional Service Pack 1 – 32 bit
- Processor: Intel(R) Core(TM) i5-2320 CPU @ 3.3GHz
- Installed Memory: 4GB
Network Adapter
- Atheros AR8151 PCI-E Gigabit Ethernet Controller (NDIS 6.20)
- Driver Provider: Atheros
- Driver Date: 22-03-2011
- Driver Version: 1.0.2.43
- Digital Signer: Microsoft Windows Hardware Compatibility Publisher
Solution
- Open Network and Sharing Center (Start >> Control Panel >> Network and Sharing Center).
- Click on Change adapter settings.
- Right click on your Local Area Connection e.g. Local Area Connection and then click Properties.
- Click Configure… button
- Select Advanced tab
- Select Large Send Offload (IPv4) or IPv4 Large Send Offload from the Property list box.
- Select Disabled from the drop down box for value.
- Click OK to save changes.
That’s it. After performing above steps I was able to resolve all issues listed in this post.
How we do it in Windows XP? (Reduce the Large Send Offload)
Ultimate network adapter settings to be done is same as discussed in this article, however steps will be different to reach network adapter properties as listed below:
1). Open Network Connections (Start >> Control Panel)
2). Right click on the Network Connection, then click Properties
3). Click Configure… button
4). Now disable large send offload option.
Please note that TCP/IP large send offload is available only on the Network Adapters which support this feature.