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Change the MTU Size for an Existing Public Cloud Network Using OpenStack CLI/API

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Learn how to change the MTU size for an existing network using OpenStack CLI/API.

Jumbo frames are Ethernet frames with more than 1,500 bytes of payload. They can carry up to 9,000 bytes of payload. Using them minimizes routing processing time. In the case of vRack, this will optimize traffic on it.
But if connectivity from a fully private instance to outside networks (Internet) is done in the network, the MTU has to be set to 1,500 bytes of payload.
The MTU size will be the same for all services using IPs in the same network.

 

Requirements

 

Instructions

Step 1: Listing networks available in the Public Cloud project

List available networks in the region:

openstack network list
 
+--------------------------------------+------------+-------------------------------------+
| ID                                   | Name       | Subnets                             |
+--------------------------------------+------------+-------------------------------------+
| 34567890-12ab-cdef-xxxx-xxxxxxxxxxxx | Ext-Net    | zzzzzzzz-yyyy-xxxx-yyyy-xxxxxxxxxxxx|
| ed85c4df-5ba6-48fb-a7d3-xxxxxxxxxxxx | openstack  | 10d5fe8b-0596-4525-a387-xxxxxxxxxxxx|
+--------------------------------------+------------+-------------------------------------+
Info

You can grab the ID of your private network (Ext-Net is a public network used for public IP addresses and is managed by OVHcloud).

 

Step 2: Displaying private network parameters

Use the following command to display the private network parameters:

openstack network show ed85c4df-5ba6-48fb-a7d3-xxxxxxxxxxxx
+---------------------------+--------------------------------------+
| Field                     | Value                                |
+---------------------------+--------------------------------------+
| admin_state_up            | UP                                   |
| availability_zone_hints   |                                      |
| availability_zones        | nova                                 |
| created_at                | 2023-01-13T08:45:06Z                 |
| description               |                                      |
| dns_domain                | None                                 |
| id                        | ed85c4df-5ba6-48fb-a7d3-xxxxxxxxxxxx |
| ipv4_address_scope        | None                                 |
| ipv6_address_scope        | None                                 |
| is_default                | None                                 |
| is_vlan_transparent       | None                                 |
| l2_adjacency              | True                                 |
| mtu                       | 9000                                 |
| name                      | openstack                            |
| port_security_enabled     | True                                 |
| project_id                | f6e0b44aa5104f689870xxxxxxxxxxxx     |
| provider:network_type     | vrack                                |
| provider:physical_network | None                                 |
| provider:segmentation_id  | 0                                    |
| qos_policy_id             | None                                 |
| revision_number           | 5                                    |
| router:external           | Internal                             |
| segments                  | None                                 |
| shared                    | False                                |
| status                    | ACTIVE                               |
| subnets                   | 10d5fe8b-0596-4525-a387-xxxxxxxxxxxx |
| tags                      |                                      |
| tenant_id                 | f6e0b44aa5104f689870bxxxxxxxxxxx     |
| updated_at                | 2023-01-13T13:43:27Z                 |
+---------------------------+--------------------------------------+

 

Step 3: Setting the new MTU size

  • Using the OpenStack CLI:
openstack network set --mtu 1500 <networkid>
  • Using the OpenStack API:
TOKEN=$(openstack token issue -c id -f value)
curl -s -H "X-Auth-Token: $TOKEN" -H "Content-Type: application/json"  -H "Accept: application/json" -X PUT -d '{"network": {"mtu": 1500}}' https://network.compute.<region>.cloud.ovh.us/v2.0/networks/<networkid>

 

Step 4: Verifying the changes

Display the private network parameters to verify that the change is applied:

openstack network show <network>

 

Step 5: Restarting the services

Updating the MTU value for an existing network with instances plugged into it requires a hard reboot of those instances that have a port in this network:

 

Go further

Browse all the Networking guides.

Browse the rest of the OVHcloud US documentation for guides on our other products and services.

Learn more about Public Cloud Network on the OVHcloud US website.