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

In the Google Cloud console, go to the VPC networkspage.

Go to VPC networks
Select a project in the project pull-down menu.
Click Create VPC network.
Enter a Namefor the network.
Choose Automaticfor the Subnet creation mode.
Set the Maximum transmission unit (MTU).

For a VM to send and receive jumbo frames, the VM's virtual NIC needs to be connected to a VPC network with a MTU value that is as large or larger than the machine MTU. Set the MTU to the largest possible value for the VM, for example 8896. If you're using GPU machines, see Jumbo frames and GPU machines .
Click Create.

Create firewall rules

Console

In the Google Cloud console, go to the Firewall policiespage.

Go to Firewall policies
Click Create firewall rule.
Enter a Namefor the firewall rule.
This name must be unique for the project.
In the Networkpull-down menu, specify the name of the network you created.
In the Targetspull-down menu, select All instances in the network.
From the Source filterpull-down menu, select IPv4 ranges.
In the field enter 10.128.0.0/16.
In Protocols and ports, select Specified protocols and ports.
Check the tcpcheckbox and enter 22in the field.
Check the Other protocolscheckbox and enter icmpin the field.
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.

In the Google Cloud console, go to the VM instancespage.

Go to VM instances
Click Create instance.
Specify a Namefor your first VM.
Click Networking, Disks, Security, Management, Sole-tenancy.
Click Networking.
In Network interfaces, click default default (10.128.0.0/20).
In the Networkpull-down menu, select the network you created.

Connect to VM instances using SSH

Console

In the Google Cloud console, go to the VM instancespage.

Go to VM instances
In the Connectcolumn of your first instance, click SSH.
In the Connectcolumn of your second instance, click SSH.

Verify MTU

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 
 
```
In the terminal for your second VM, install tcpdump :
```
sudo apt-get install tcpdump --yes
```
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
```
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
```

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.

On your second VM, press Ctrl-c to stop tcpdump .
When you're done testing, delete your resources in the following order:
1. Firewall rule and VM instances
2. VPC network

What's next

Learn more about MTU .
Create a VPC network with a specified MTU .