# `add_v4_net` Command

## Name

`add_v4_net`

## Synopsis

```
add_v4_net ${card} ${vlan} ${group}
```

## Description

Adds an internal network segment with the specified vlan on the specified
card.  The created vlan-adaptor is put into the specified group.  It is setup
for IPv4.

If `${vlan}` is 0, then no tagged VLAN interfaces will be created; however,
the subnet address computations will still be performed as-if the vlan
were created.  This means that `xy0` will use `0` for its subnet
computations in IPv4.  If you don't intend to use
VLANs for subnets, just use VLAN ID 0 when declaring networks.


The IPv4 network will be a `/24` under `${v4_net_xy0}` if `${card}` is
`xy0`, for example.  If `${v4_net_xy0}` is not set, then `${v4_net}` is
used by default.  The 3rd octet will be `$(( ${vlan}/10 + ${vlan}%10 ))`.  For
example, if `${vlan}` is `102` and `${v4_net}` is `172.18`, then the configured
v4 network will be `172.18.12.0/24` and the router will hold address
`172.18.12.1`.  By default, IPv4 network DHCP configuration is enabled and
the range `.100` to `.200` will be used as a dynamic allocation pool.

Internally, this will call [`add_vlan`](add_vlan.md), passing it `${card}` and
`${vlan}`.

## Subnet Calculation

(It is strongly recommended that the 10s digit and 1000s digit of the VLAN ID be
kept as `0`, as those digits are reserved for future improvements.  While this
limits the system to 100 vlans, it provides 1:1 visual alignment between IPv4,
IPv6, and VLAN ID.  Each can be visually compared to the others.)

|VLAN|IPv4 (3rd octet)|Example IPv4   |
|---:|---------------:|--------------:|
|   0| 0              |192.168.0.0/24 |
|   7| 7              |192.168.7.0/24 |
| 101|11              |192.168.11.0/24|
| 205|25              |192.168.25.0/24|
| 900|90              |192.168.90.0/24|

## Options

 - `isp=${NAME}` - Attach this network to a specified ISP's configuration
 - `no_isp` - This network should not be associated with any ISP (future expansion).

## Examples

#### Basic home LAN
`add_v4_net abc2 100 main`

#### Guest network with no ULA
`add_v4_net xy2 102 guest`

#### IoT network with no ISP association
`add_v4_net xy2 103 iot no_isp`

#### Management network on a different ISP
`add_v4_net xy2 402 mgmt isp=fios_1`


## See Also

 - [`add_net`](add_net.md)
 - [`add_v6_net`](add_v6_net.md)
 - [`add_vlan`](add_vlan.md)