# How to increase the network bandwidth You can increase the network bandwidth of your LXD setup by configuring the transmit queue length (`txqueuelen`). This change makes sense in the following scenarios: - You have a NIC with 1 GbE or higher on a LXD host with a lot of local activity (instance-instance connections or host-instance connections). - You have an internet connection with 1 GbE or higher on your LXD host. The more instances you use, the more you can benefit from this tweak. #### NOTE The following instructions use a `txqueuelen` value of 10000, which is commonly used with 10GbE NICs, and a `net.core.netdev_max_backlog` value of 182757. Depending on your network, you might need to use different values. In general, you should use small `txqueuelen` values with slow devices with a high latency, and high `txqueuelen` values with devices with a low latency. For the `net.core.netdev_max_backlog` value, a good guideline is to use the minimum value of the `net.ipv4.tcp_mem` configuration. ## Increase the network bandwidth on the LXD host Ubuntu >= 18.04 Complete the following steps to increase the network bandwidth on the LXD host: 1. Increase the transmit queue length (`txqueuelen`) of both the real NIC (for example, `enp5s0f1`) and the LXD NIC (for example, `lxdbr0`). To make the change permanent, create a file named `/etc/udev/rules.d/60-custom-txqueuelen.rules` with the following content: ```none KERNEL=="enp5s0f1", RUN+="/sbin/ip link set %k txqueuelen 10000" KERNEL=="lxdbr0", RUN+="/sbin/ip link set %k txqueuelen 10000" ``` Apply the above `udev` rules via: ```none udevadm trigger ``` 2. Increase the receive queue length (`net.core.netdev_max_backlog`). To make the change permanent, add the following configuration to `/etc/sysctl.conf`: ```none net.core.netdev_max_backlog = 182757 ``` Apply the above `sysctl.conf` change via: ```none sysctl -p ``` Ubuntu <= 17.04 Complete the following steps to increase the network bandwidth on the LXD host: 1. Increase the transmit queue length (`txqueuelen`) of both the real NIC and the LXD NIC (for example, `lxdbr0`). You can do this temporarily for testing with the following command: ```none ifconfig txqueuelen 10000 ``` To make the change permanent, add the following command to your interface configuration in `/etc/network/interfaces`: ```none up ip link set eth0 txqueuelen 10000 ``` 2. Increase the receive queue length (`net.core.netdev_max_backlog`). You can do this temporarily for testing with the following command: ```none echo 182757 > /proc/sys/net/core/netdev_max_backlog ``` To make the change permanent, add the following configuration to `/etc/sysctl.conf`: ```none net.core.netdev_max_backlog = 182757 ``` ## Increase the transmit queue length on the instances You must also change the `txqueuelen` value for all Ethernet interfaces in your instances. To do this, use one of the following methods: - Apply the same changes as described above for the LXD host. - Set the `queue.tx.length` device option on the instance profile or configuration. For example, to do this for the LXD default profile: ```none lxc profile device set default eth0 queue.tx.length "10000" ```