| 1 | <?xml version="1.0" encoding="UTF-8"?>
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| 2 | <!DOCTYPE topic
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| 3 | PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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| 4 | <topic xml:lang="en-us" id="network_performance">
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| 5 | <title>Improving Network Performance</title>
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| 6 |
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| 7 | <body>
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| 8 | <p><ph conkeyref="vbox-conkeyref-phrases/product-name"/> provides a variety of virtual network adapters
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| 9 | that can be attached to the host's network in a number of ways. Depending on which types of adapters and
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| 10 | attachments are used the network performance will be different. Performance-wise the virtio network adapter is
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| 11 | preferable over Intel PRO/1000 emulated adapters, which are preferred over the PCNet family of adapters. Both
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| 12 | virtio and Intel PRO/1000 adapters enjoy the benefit of segmentation and checksum offloading. Segmentation
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| 13 | offloading is essential for high performance as it allows for less context switches, dramatically increasing the
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| 14 | sizes of packets that cross the VM/host boundary. </p>
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| 15 | <note>
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| 16 | <p>Neither virtio nor Intel PRO/1000 drivers for Windows XP support segmentation offloading. Therefore
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| 17 | Windows XP guests never reach the same transmission rates as other guest types. Refer to MS Knowledge base
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| 18 | article 842264 for additional information. </p>
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| 19 | </note>
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| 20 | <p>Three attachment types: Internal, Bridged, and Host-Only, have nearly identical performance. The
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| 21 | Internal type is slightly faster and uses less CPU cycles as the packets never reach the host's network stack. The
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| 22 | NAT attachment type is the slowest and most secure of all attachment types, as it provides network address
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| 23 | translation. The generic driver attachment is special and cannot be considered as an alternative to other
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| 24 | attachment types. </p>
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| 25 | <p>The number of CPUs assigned to VM does not improve network performance and in some cases may hurt it
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| 26 | due to increased concurrency in the guest. </p>
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| 27 | <p>Here is a short summary of things to check in order to improve network performance: </p>
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| 28 | <ul>
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| 29 | <li>
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| 30 | <p>Whenever possible use the virtio network adapter. Otherwise, use one of the Intel PRO/1000
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| 31 | adapters. </p>
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| 32 | </li>
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| 33 | <li>
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| 34 | <p>Use a Bridged attachment instead of NAT. </p>
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| 35 | </li>
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| 36 | <li>
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| 37 | <p>Ensure segmentation offloading is enabled in the guest OS. Usually it will be enabled by
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| 38 | default. You can check and modify offloading settings using the <userinput>ethtool</userinput> command on
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| 39 | Linux guests. </p>
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| 40 | </li>
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| 41 | <li>
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| 42 | <p>Perform a full detailed analysis of network traffic on the VM's network adaptor using a third
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| 43 | party tool such as Wireshark. To do this, a promiscuous mode policy needs to be used on the VM's network
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| 44 | adaptor. Use of this mode is only possible on the following network types: NAT Network, Bridged Adapter,
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| 45 | Internal Network, and Host-Only Adapter. </p>
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| 46 | <p>To setup a promiscuous mode policy, either set the <uicontrol>Promiscuous Mode</uicontrol> in the <uicontrol>Network</uicontrol> section of the VM's <uicontrol>Settings</uicontrol> for the network adaptor, or use the command line tool <userinput>VBoxManage</userinput>. See <xref href="../cli_topics/vboxmanage-modifyvm.dita"/>.</p>
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| 47 | <p>Promiscuous mode policies are as follows: </p>
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| 48 | <ul>
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| 49 | <li>
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| 50 | <p><codeph>deny</codeph>, which hides any traffic not intended for the VM's network adaptor.
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| 51 | This is the default setting. </p>
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| 52 | </li>
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| 53 | <li>
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| 54 | <p><codeph>allow-vms</codeph>, which hides all host traffic from the VM's network adaptor,
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| 55 | but allows it to see traffic from and to other VMs. </p>
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| 56 | </li>
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| 57 | <li>
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| 58 | <p><codeph>allow-all</codeph>, which removes all restrictions. The VM's network adaptor sees
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| 59 | all traffic. </p>
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| 60 | </li>
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| 61 | </ul>
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| 62 | </li>
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| 63 | </ul>
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| 64 | </body>
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| 65 |
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| 66 | </topic>
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