Sun Microsystems VERSION 3.1.0_BETA2 user manual Tuning TCP/IP buffers for NAT

9 Advanced topics

This command would reserve the network addresses 192.168.0.0 ...

192.168.254.254 for the first NAT network instance of “My VM”. The guest IP would be assigned to 192.168.0.15 and the default gateway could be found at 192.168.0.2.

9.13.2Configuring the boot server (next server) of a NAT network interface

For network booting in NAT mode, by default VirtualBox uses a built-in TFTP server at the IP address 10.0.2.3. This default behavior should work fine for typical remote- booting scenarios. However, it is possible to change the boot server IP and the location of the boot image with the following commands:

VBoxManage setextradata "Linux Guest" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/NextServer" 10.0.2.2

VBoxManage setextradata "Linux Guest" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/BootFile" /srv/tftp/boot/MyPXEBoot.pxe

9.13.3 Tuning TCP/IP buffers for NAT

The VirtualBox NAT stack performance is often determined by its interaction with the host’s TCP/IP stack and the size of several buffers (SO_RCVBUF and SO_SNDBUF). For certain setups users might want to adjust the buffer size for better performance. This can by achieved using the following commands (values are in kilobytes and can range from 8 to 1024):

VBoxManage setextradata "Linux Guest" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/SocketRcvBuf" 128

VBoxManage setextradata "Linux Guest" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/SocketSndBuf" 128

VBoxManage setextradata "Linux Guest" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/TcpRcvSpace" 128

VBoxManage setextradata "Linux Guest" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/TcpSndSpace" 128

Each of these buffers has a default size of 64KB.

9.13.4 Binding NAT sockets to a specific interface

By default, VirtualBox’s NAT engine will route TCP/IP packets through the default port assigned by the host’s TCP/IP stack. (The technical reason for this is that the NAT engine uses sockets for communication.) If, for some reason, you want to change this behavior, you can tell the NAT engine to bind to a particular IP address instead. Use the following command:

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