A lot more documentation.

docs/add_v6_net.md

@@ -37,6 +37,47 @@ on those prefixes.
 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
+IPv6 and VLAN ID.  Each can be visually compared to the other.)
+
+|VLAN|IPv6 suffix (hex)|Example IPv6            |
+|---:|----------------:|-----------------------:|
+|   7|  7              |2001:db8:abcd:ef07:::/64|
+| 101| 11              |2001:db8:abcd:ef11:::/64|
+| 205| 25              |2001:db8:abcd:ef25:::/64|
+| 900| 90              |2001:db8:abcd:ef25:::/64|
+
+## Options
+
+ - `no_ula` - Do not create a Unique Local Address for this network.
+ - `isp=${NAME}` - Attach this network to a specified ISP's configuration
+ - `no_isp` - This network should not be associated with any ISP (declines to
+   add network to DHCPv6 PD, among other things).
+
+## Examples
+
+#### Basic home LAN
+`add_v6_net abc2 100 main`
+
+#### Guest network with no ULA
+`add_v6_net xy2 102 guest no_ula`
+
+#### IoT network with no ULA and no ISP prefix delegation
+`add_v6_net xy2 103 iot no_ula no_isp`
+
+#### Management network on a different ISP PD
+`add_v6_net xy2 402 mgmt isp=fios_1`
+
+#### Servers network with no ULA and no ISP prefix delegation and a dedicated static prefix
+`add_v6_net xy2 402 hosting no_ula no_isp 2001:db8:1ab:42::`
+
+(This form is useful if you have your own `/48` or similar for your self-hosted
+services, and that prefix gets routed to you over tunnels.)
+
 ## See Also
 
  - [`add_net`](add_net.md)