IP Addressing
Address Space Overview
| Family | Scope | Prefix | Size |
|---|---|---|---|
| IPv4 | Private (RFC 1918) | 10.37.0.0/16 |
65,536 addresses |
| IPv6 | ULA (RFC 4193) | fda8:288c:4f37::/48 |
65,536 × /64 subnets |
| IPv6 | GUA (ISP delegation) | ISP-delegated /56 | 256 × /64 subnets |
The site code 37 in 10.37.0.0/16 was chosen arbitrarily from the 10.0.0.0/8 space to avoid collision with common defaults (e.g. 10.0.x.x, 10.1.x.x).
VLAN-to-Subnet Convention
VLANs are numbered 0–255. The VLAN ID maps deterministically to subnets across all three address families, using decimal for IPv4 and hex for IPv6.
IPv4
10.37.<vlan>.0/24
Each VLAN gets a /24. The VLAN ID is the decimal third octet.
IPv6 ULA
fda8:288c:4f37:<vlan_hex>00::/64
The VLAN ID in two-digit hex occupies the high byte of the 4th hextet. The low byte is always 00.
The /48 prefix gives 16 bits of subnet space; only the high 8 bits are used, reserving the low byte for potential future use.
IPv6 GUA
<isp-prefix>:<vlan_hex>::/64
The ISP delegates a /56, giving 8 bits of subnet space. The VLAN ID in two-digit hex fills those 8 bits directly.
Subnet Derivation Examples
| VLAN | Decimal | Hex | IPv4 | IPv6 ULA |
|---|---|---|---|---|
| 1 | 1 | 01 |
10.37.1.0/24 |
fda8:288c:4f37:0100::/64 |
| 10 | 10 | 0a |
10.37.10.0/24 |
fda8:288c:4f37:0a00::/64 |
| 176 | 176 | b0 |
10.37.176.0/24 |
fda8:288c:4f37:b000::/64 |
| 255 | 255 | ff |
10.37.255.0/24 |
fda8:288c:4f37:ff00::/64 |
Notes
- The ISP-delegated GUA /56 is the binding constraint: 256 subnets maximum, which aligns exactly with VLAN 0–255.
- The ULA /48 could theoretically support 65,536 /64 subnets, but is deliberately kept consistent with the GUA scheme for simplicity.
- VLAN 0 is reserved (IEEE 802.1Q native VLAN). Avoid assigning it to a routed segment.