A lot more documentation.

docs/add_v4_net.md

@@ -7,7 +7,7 @@
 ## Synopsis
 
 ```
-add_v4_net ${card} ${vlan} ${group} [{no_ula|isp=abc|no_isp}...]
+add_v4_net ${card} ${vlan} ${group} [{isp=abc|no_isp}...]
 ```
 
 ## Description
@@ -27,6 +27,40 @@ 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   |
+|---:|---------------:|--------------:|
+|   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_net abc2 100 main`
+
+#### Guest network with no ULA
+`add_net xy2 102 guest no_ula`
+
+#### IoT network with no ULA and no ISP prefix delegation
+`add_net xy2 103 iot no_ula no_isp`
+
+#### Management network on a different ISP PD
+`add_net xy2 402 mgmt isp=fios_1`
+
+
 ## See Also
 
  - [`add_net`](add_net.md)