# Subnets
## Subnet Introduction
In the **VPC Networking > Subnets** view, an IP subnet can be defined in
a standard CIDR format, and assigned a name for easy reference throughout
the UI. It is used primarily for association with a VPC as described in
[VPC Introduction](networking-vpc.md#vpcinneokarm-virtualprivatecloud-vpc). VPC subnets are defined by the
following constraints:
1. The first four IP addresses and the last IP address in each subnet CIDR
block are not available for users, and cannot be assigned to an instance.
2. The second address of the subnet is reserved for the router.
3. The CIDR block of a subnet may be either identical to the VPC’s CIDR block,
which is the case when there is a single subnet, or a subset of the VPC’s
CIDR block, when there are multiple subnets. In the latter case, the CIDR
blocks of the subnets cannot overlap. The permitted block size ranges from
a /28 netmask to a /16 netmask.
4. Every subnet that is created is automatically associated with the main
route table of the VPC. You can change the association. A subnet can be
associated with only one route table at a time.
## Creating a Subnet
See the video introducing the basics of creating and configuring
zCompute VPC Subnets:
**To create a subnet:**
1. Navigate to the **VPC Networking > Subnets** view.
2. From the top toolbar, click **Create**.
3. In the **Create Subnet** dialog, enter the following:
* **Name** - name of the subnet.
* **Description** - optional description of the subnet.
* **VPC** - VPC which is associated with this subnet.
* **CIDR** - subnet in CIDR format based on IP/mask.
* **Tags** - optionally add tags by selecting them from the dropdown, or
creating them in this field.
## Subnet Operations
After creating a subnet, it is displayed in the subnet list
in the **VPC Networking > Subnets** view. The following operations can
be performed by selecting a subnet from the list, and clicking the
appropriate icon.
**From top toolbar:**
* **Modify** - change the name of the subnet.
* **Set Default** - set the subnet as the default for a VPC, to be used for
: provisioning new entities within the VPC. For example, if a new VM instance
is associated with a VPC, it will be configured with an IP from the default
subnet.
* **Delete**
* **Test connectivity** - use ping or arping to test connectivity
to a specific IP within the selected subnet. For more information on subnet
testing, see [Testing Subnet Connectivity](#test-subnet).
* **Soft Reset** - rebind all DHCP ports on the network.
* **Hard Reset** - recreate DHCP servers on the network.
**From lower toolbar:**
* **VMs** - view information on VMs associated with the selected subnet.
* **Events** - view configuration events (info) or alarms for the subnet.
In the displayed subnet list, there is an indication of [Direct Subnet](#direct-subnet).
### Direct Subnet
In zCompute, a Direct Subnet provides the ability to share the same layer 2
network (VLAN) between the hosting data center’s network and a VPC subnet.
This allows end users who require it, to achieve L2 connectivity over a
given VLAN ID to resources external to the zCompute cluster, or direct
access to zStorage resources available at the data center.
For example, a direct subnet allows the establishment of external and
dedicated VPSA Storage Arrays and Object Storages while bypassing
unnecessary internet routers.
This is extremely common and useful where a dedicated and high-speed
NAS/Object Storage solution is required.
See the video introducing the basics of connecting local networks into
your VPC with Direct Subnets:
#### Creating a Direct Subnet
To create a direct subnet (MSP or Zadara Operations team only):
1. Navigate to **Account Networking > Direct Subnets** and click
**+ Create**.
2. In the **Create Direct Subnet** window, enter:
* **Name**: The name of the direct subnet.
* **Description**: Optional description for the direct subnet.
* **Project**: From the dropdown, select the project to which this
direct subnet will be associated.
* **VPC**: Optionally, from the dropdown, select the VPC for this
direct subnet.
* **Node Network**: Select the network from the dropdown.
* **VLAN ID**: The VLAN ID of the physical switches that the direct
subnet will use.
This VLAN ID should also be configured on Zadara switches by
Zadara Operations, for all the switch ports attached to zCompute
nodes as well as the switches’ uplinks to the partner’s upstream
switches, and the partner’s switches’ links to Zadara’s switches.
* **Subnet (CIDR)**: The direct subnet’s CIDR block.
Typically, this CIDR is provided by the partner, to make it routable
from the partner’s data center.
* **VPC Internal Router IP**: The first IP address of the CIDR block.
The subnet’s virtual router is created by zCompute, and used by
payloads created within zCompute to route traffic from the subnet.
* **External Router IP**: Optional IP address for the VPC’s external
router.
* **Allocation Pools**:
One or more ranges of IP addresses allocated for zCompute payloads
of this subnet.
Enter the start and end IP addresses of the range of addresses
comprising the pool of addresses, from which subnets can be
allocated.
To configure an additional pool of IP addresses, click **Add** and
enter the pool’s start and end IP addresses.
3. Click **Finish**.
The subnet is immediately available on the specified VPC.
#### Control over VPC Subnet MTU
Users can view and change MTU values per virtual network.
* The relevant networks are:
: * Edge networks (for MSP administrators only)
* Direct networks (subnets)
* VPC subnets
* The **minimum** allowed MTU value is 1450 for standard VPC subnets or 1500
for direct subnets or edge networks.
* The **maximum** allowed MTU value depends on the global MTU configured in
the cluster (e.g. 9000 or 1500). If the global MTU configured in the
cluster is 9000, the maximum allowed MTU value for all virtual networks
will be limited to 8950.
* If a VM experiences MTU-related connectivity issues and it resides on a
public network (connected via a route-table to an internet-gateway),
then it is recommended to set that network MTU to no more than 1500.
##### Modify Edge Network MTU
1. Navigate to **Region Networking > Edge Networks**
2. In the Edge Networks list, select the Edge Network to modify.
3. In the selected Edge Network’s detail view, on the top menu click **Edit**.
4. In the **Modify Edge Network** dialog, update the **MTU** value.
Click **Finish** to save the updated MTU value.
##### Modify Direct Subnet MTU
1. Navigate to **Account Networking > Direct Subnets**
2. In the Direct Subnets list, select the Direct Subnet to modify.
3. In the selected Direct Subnet’s detail view, on the top menu click **Edit**.
4. In the **Modify Direct Subnet** dialog, update the **MTU** value.
Click **Finish** to save the updated MTU value.
##### Modify VPC Subnet MTU
1. Navigate to **VPC Networking > Subnets**
2. In the Subnets list, select the Subnet to modify.
3. In the selected Subnet’s detail view, on the top menu click **Modify**.
4. In the **Modify Subnet** dialog, update the **MTU** value.
Click **Ok** to save the updated MTU value.
#### Routing traffic through an external router
If you want to route traffic from the VPC through an external router
connected to the Direct Subnet, the VPC route table associated with the
Direct Subnet should be modified.
This can be configured with end user’s tenant permissions.
1. If an **External Router IP** was defined in [Creating a Direct Subnet](#creating-direct-subnet),
skip to the next step to update the Route Table.
Otherwise, create an Elastic Network Interface:
1. Navigate to **VPC Networking > Network Interfaces** and click
**+ Create**.
2. In the **Create Elastic Network Interface** dialog, enter:
* **Name**: The interface name.
* **Description**: Optional description text.
* **VPC**: The VPC for which the external router is being added.
* **Subnet**: From the dropdown, select the Direct Subnet.
* **Private IP**: The external router’s IP address.
* **Security Groups**: From the dropdown, select the security groups
to apply to the network interface.
3. Click **Finish**.
2. Navigate to **VPC Networking > Route Tables** and click the name of the
Route Table to update.
1. In the selected Route Table’s lower pane,
click **+ Create**.
* **Destination CIDR**: The destination network or networks.
* **Target Type**: Select **Network Interface** from the dropdown,
to display the Network Interface input prompt.
* **Network Interface**: From the dropdown, select the network
interface created in the previous step.
2. Click **OK**.
## Testing Subnet Connectivity
Connectivity between a VPC Subnet and a specific IP address can be tested
by ping, using either the GUI or CLI.
**Using the GUI**
1. Navigate to the **VPC Networking** > **Subnets** view.
2. Select a subnet from the displayed list and click **Test Connectivity** in
top toolbar.
3. In the **Test Connectivity** window, enter a Destination IP address.
4. Select **ping** or **arping**.
5. Click **OK**.
6. Click **OK**. A message is displayed that the connectivity test is taking place.
7. A few seconds later, the test results will be displayed indicting success
or failure as well as other relevant details. This status report is also
available in the right-hand sidebar.
**Using the CLI**
1. The ‘guestnet-admin-tool ping-ip create’ command with which you can test
a subnet’s connectivity requires the ID of the given subnet
(see ‘entity_id’ below).
Note: ‘–command-type’ is either ‘ping’ (default) or ‘arping’
```default
guestnet-admin-tool ping-ip create [-h]
[-f {adaptive_table,json,shell,table,value,yaml}]
[-c COLUMN] [--max-width ]
[--noindent] [--prefix PREFIX]
[-m [NAME=VALUE [NAME=VALUE ...]]]
[--command-type COMMAND_TYPE]
[--name NAME]
entity_id dest_ip
```
2. Run the ‘vpc network list’ command to locate the ID of Subnet-1.
```default
vpc network list -c id -c name
```
3. This returns a list of subnets and their IDs.
```default
+--------------------------------------+-----------------------------------------------------+
| id | name |
+======================================+=====================================================+
| ceff2b60-fb75-44d0-8b1a-ac4034b260dc | Subnet-1 |
+--------------------------------------+-----------------------------------------------------+
```
4. Test the connectivity of Subnet-1 to the destination IP address 8.8.8.8.
```default
guestnet-admin-tool ping-ip create ceff2b60-fb75-44d0-8b1a-ac4034b260dc 8.8.8.8
```
5. This returns a temporary, pending status of the subnet’s connectivity.
```default
+--------------+--------------------------------------+
| id | 2ce18cc5-b1a8-401c-ae98-99e484f99b3e |
| name | none |
| status | pending |
| command_type | ping |
| created_at | 2019-05-12T13:39:56.650560 |
| dest_ip | 8.8.8.8 |
| entity_id | ceff2b60-fb75-44d0-8b1a-ac4034b260dc |
| output | - |
| project_id | 07650a05e9dd47c8a3b874a2132e178c |
| updated_at | 2019-05-12T13:39:56.650581 |
| user_id | admin |
+--------------+--------------------------------------+
```
6. Wait a few seconds and then request the final status of Router-1’s connectivity
test by using the ‘guestnet-admin-tool ping-ip get ping_ip_id’, as follows:
```default
guestnet-admin-tool ping-ip get 2ce18cc5-b1a8-401c-ae98-99e484f99b3e
```
7. This returns the final, succeeded/failed status of Router-1’s connectivity
test with relevant output details.
```default
+--------------+----------------------------------------------------------------+
| id | 2ce18cc5-b1a8-401c-ae98-99e484f99b3e |
| name | none |
| status | succeeded |
| command_type | ping |
| created_at | 2019-05-12T13:39:56 |
| dest_ip | 8.8.8.8 |
| entity_id | ceff2b60-fb75-44d0-8b1a-ac4034b260dc |
| +----------------------------------------------------------------+
| output | PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data. |
| | 64 bytes from 8.8.8.8: icmp_seq=1 ttl=118 time=55.1 ms |
| | 64 bytes from 8.8.8.8: icmp_seq=2 ttl=118 time=53.3 ms |
| | |
| | --- 8.8.8.8 ping statistics --- |
| | 2 packets transmitted, 2 received, 0% packet loss, time 1001ms |
| | rtt min/avg/max/mdev = 53.335/54.219/55.104/0.914 ms |
| | |
| +----------------------------------------------------------------+
| project_id | 07650a05e9dd47c8a3b874a2132e178c |
| updated_at | 2019-05-12T13:39:59 |
| user_id | admin |
+--------------+----------------------------------------------------------------+
```
## Additional options for Subnet (VPC) Connectivity Testing
1. Delete a specific subnet connectivity test
```default
guestnet-admin-tool ping-ip delete ping_ip_id
```
2. List all ping_ip requests
```default
guestnet-admin-tool ping-ip list
```