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¶

Complete the following steps to increase the network bandwidth on the LXD host:

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:
```
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:
```
 udevadm trigger
```
Increase the receive queue length (net.core.netdev_max_backlog). To make the change permanent, add the following configuration to /etc/sysctl.conf:
```
net.core.netdev_max_backlog = 182757
```
Apply the above sysctl.conf change via:
```
 sysctl -p
```

Complete the following steps to increase the network bandwidth on the LXD host:

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:
```
ifconfig <interface> txqueuelen 10000
```
To make the change permanent, add the following command to your interface configuration in /etc/network/interfaces:
```
up ip link set eth0 txqueuelen 10000
```
Increase the receive queue length (net.core.netdev_max_backlog). You can do this temporarily for testing with the following command:
```
echo 182757 > /proc/sys/net/core/netdev_max_backlog
```
To make the change permanent, add the following configuration to /etc/sysctl.conf:
```
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:
```
 lxc profile device set default eth0 queue.tx.length "10000"
```