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Setting link impairments#

With the containerlab tools netem set command users can set link impairments on a specific interface of a container. The following list of link impairments is supported:

  • delay & jitter
  • packet loss
  • rate limiting
Considerations

Note, that netem is a Linux kernel module and it might not be available in particular kernel configurations.

For example, on some RHEL 8 systems the following commands might be needed to run to add the support for netem:

dnf install kernel-debug-modules-extra
dnf install kernel-modules-extra
systemctl reboot now

Note, that setting link impairments with netem set command is implemented in a way that all impairments are applied to the interface at once. This means that if an interface had a packet loss of 10% and you execute netem set command with a delay of 100ms, the packet loss will be reset to 0% and the delay will be set to 100ms.

Once the impairments are set, they act for as long as the underlying node/container is running. To clear the impairments, set them to the default values.

Usage#

containerlab tools netem set [local-flags]

Flags#

node#

With the mandatory --node | -n flag a user specifies the name of the containerlab node to set link impairments on.

interface#

With the mandatory --interface | -i flag a user specifies the name of the interface to set link impairments on. This can also be the interface alias, if one is used.

delay#

With the --delay flag a user specifies the delay to set on the interface. The delay is specified in duration format. Example: 50ms, 3s.

Default value is 0s.

jitter#

Delay variation, aka jitter, is specified with the --jitter flag. The jitter is specified in duration format and can only be used if --delay is specified. Example: 5ms.

Default value is 0s.

loss#

Packet loss is specified with the --loss flag. The loss is specified in percentage format. Example: 10.

rate#

Egress rate limiting is specified with the --rate flag. The rate is specified in kbit per second format. Example: value 100 means rate of 100kbit/s.

Examples#

Setting delay and jitter#

For clab-netem-r1 node and its eth1 interface set delay of 5ms and jitter of 1ms:

containerlab tools netem set -n clab-netem-r1 -i eth1 --delay 5ms --jitter 1ms

Setting packet loss#

setting packet loss at 10% rate
containerlab tools netem set -n clab-netem-r1 -i eth1 --loss 10

Clear any existing impairments#

containerlab tools netem set -n clab-netem-r1 -i eth1
+-----------+-------+--------+-------------+-------------+
| Interface | Delay | Jitter | Packet Loss | Rate (kbit) |
+-----------+-------+--------+-------------+-------------+
| eth1      | 0s    | 0s     | 0.00%       |           0 |
+-----------+-------+--------+-------------+-------------+

The above command will use default values for all supported link impairments, which is 0s for delay and jitter, 0 for loss and 0 for rate.