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Create and verify a jumbo frame MTU network

This page walks you through creating a Virtual Private Cloud (VPC) network and a pair of VMs for testing. It assumes you are generally familiar with network MTU.

Create an auto mode VPC network

Console

  1. Go to the VPC networks page in the Google Cloud console.
    Go to VPC networks
  2. Select a project in the project pull-down menu.
  3. Click Create VPC network.
  4. Enter a Name for the network.
  5. Choose Automatic for the Subnet creation mode.
  6. Set the Maximum transmission unit (MTU) field to 8896.
  7. Click Create.

Create firewall rules

Console

  1. Go to the Firewall page in the Google Cloud console.
    Go to the Firewall page
  2. Click Create firewall rule.
  3. Enter a Name for the firewall rule.
    This name must be unique for the project.
  4. In the Network pull-down menu, specify the name of the network you created.
  5. In the Targets pull-down menu, select All instances in the network.
  6. From the Source filter pull-down menu, select IPv4 ranges.
  7. In the field enter 10.128.0.0/16.
  8. In Protocols and ports, select Specified protocols and ports.
  9. Check the tcp checkbox and enter 22 in the field.
  10. Check the Other protocols checkbox and enter icmp in the field.
  11. Click Create.

Create VMs

This section shows you how to create two VM instances for testing.

Console

Do these steps twice to get two VMs in the same zone.

  1. In the Google Cloud console, go to the VM instances page.

    Go to VM instances

  2. Click Create instance.

  3. Specify a Name for your first VM.

  4. Click Networking, Disks, Security, Management, Sole-tenancy.

  5. Click Networking.

  6. In Network interfaces, click default default (10.128.0.0/20).

  7. In the Network pull-down menu, select the network you created.

Connect to VM instances using SSH

Console

  1. In the Google Cloud console, go to the VM instances page.

    Go to VM instances

  2. In the Connect column of your first instance, click SSH.

  3. In the Connect column of your second instance, click SSH.

Verify MTU

  1. In the terminal for your first VM, run the following command:

    /sbin/ifconfig | grep mtu
    

    The reported MTU should be 8896.

    ens4: flags=4163  mtu 8896
    lo: flags=73  mtu 65536
    

  2. In the terminal for your second VM, install tcpdump:

    sudo apt-get install tcpdump --yes
    

  3. In the terminal of your second VM, start tcpdump. Replace FIRST_VM_NAME with the name of your first VM.

    sudo tcpdump host FIRST_VM_NAME -v
    

  4. In the terminal of your first VM, ping your second VM. The ping command must specify a packet size that is 28 bytes smaller than the network MTU. Replace SECOND_VM_NAME with the name of your second VM.

    ping SECOND_VM_NAME -c 10 -M do -s 8868
    

  5. Check your second VM. You should see something like the following:

    tcpdump: listening on ens4, link-type EN10MB (Ethernet), snapshot length 262144 bytes
    19:43:57.116005 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 8896)
    FIRST_VM_NAME.c.PROJECT_ID.internal > SECOND_VM_NAME.c.PROJECT_ID.internal: ICMP echo request, id 5253, seq 1, length 8876
    19:43:57.116053 IP (tos 0x0, ttl 64, id 23961, offset 0, flags [none], proto ICMP (1), length 8896)
    SECOND_VM_NAME.c.PROJECT_ID.internal > FIRST_VM_NAME.c.PROJECT_ID.internal: ICMP echo reply, id 5253, seq 1, length 8876
    

    The variables mean the following:

    • FIRST_VM_NAME is a name of your first VM.
    • SECOND_VM_NAME is a name of your second VM.
    • PROJECT_ID is the ID of the project containing the VMs.
  6. On your second VM, press Ctrl-c to stop tcpdump.

  7. When you're done testing, delete your resources in the following order:

    1. Firewall rule and VM instances
    2. VPC network

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