IPv4 + IPv6

NETWORK TOOLKIT / 02

Subnet Planner.

Allocate subnets, reserve capacity, and plan for growth.

Plan Settings

Opening local plans…

Plan Name

Parent Network

Allocation Profile

Host Growth Allowance (%)

Applies to host counts before choosing subnet sizes; fixed prefixes and reserved blocks are unchanged.

DNS Defaults & Plan Files

DNS Search Domains

Separate domains with commas or spaces.

DNS Resolver Addresses

Resolver IPs for the plan; no DNS records or device settings are changed.

Subnet Allocations 3

Largest subnets are placed first. Fixed CIDRs keep their addresses; reserved blocks are excluded.

Subnet requirements and applied allocations
Name / VLAN	Requirement	Allocated CIDR	Usable IPv4 / Type	Actions
Staff NetworkVLAN 10	100hosts + 0% growth	Awaiting Allocation	—
VoiceVLAN 20	40hosts + 0% growth	Awaiting Allocation	—
Guest Wi-FiVLAN 30	60hosts + 0% growth	Awaiting Allocation	—

Staff NetworkVLAN 10 · hosts

Awaiting AllocationRequirement: 100 · Usable IPv4 / Type: —

VoiceVLAN 20 · hosts

Awaiting AllocationRequirement: 40 · Usable IPv4 / Type: —

Guest Wi-FiVLAN 30 · hosts

Awaiting AllocationRequirement: 60 · Usable IPv4 / Type: —

Address Space Usage

10.20.0.0/22

Preview and apply your allocations to see the space remaining.

Download a JSON backup before moving devices or clearing browser data.

NETWORK TOOLKIT / 04

Network Reference.

Prefix sizes, address capacity and provider rules.

Prefix Reference

IPv4 prefix reference
Prefix	Subnet Mask	Total Addresses	Usable (Standard)
/0	0.0.0.0	4294967296	4294967294
/1	128.0.0.0	2147483648	2147483646
/2	192.0.0.0	1073741824	1073741822
/3	224.0.0.0	536870912	536870910
/4	240.0.0.0	268435456	268435454
/5	248.0.0.0	134217728	134217726
/6	252.0.0.0	67108864	67108862
/7	254.0.0.0	33554432	33554430
/8	255.0.0.0	16777216	16777214
/9	255.128.0.0	8388608	8388606
/10	255.192.0.0	4194304	4194302
/11	255.224.0.0	2097152	2097150
/12	255.240.0.0	1048576	1048574
/13	255.248.0.0	524288	524286
/14	255.252.0.0	262144	262142
/15	255.254.0.0	131072	131070
/16	255.255.0.0	65536	65534
/17	255.255.128.0	32768	32766
/18	255.255.192.0	16384	16382
/19	255.255.224.0	8192	8190
/20	255.255.240.0	4096	4094
/21	255.255.248.0	2048	2046
/22	255.255.252.0	1024	1022
/23	255.255.254.0	512	510
/24	255.255.255.0	256	254
/25	255.255.255.128	128	126
/26	255.255.255.192	64	62
/27	255.255.255.224	32	30
/28	255.255.255.240	16	14
/29	255.255.255.248	8	6
/30	255.255.255.252	4	2
/31	255.255.255.254	2	2
/32	255.255.255.255	1	1

1–33 of 33 rows

Standard Networking

IPv4 LANs reserve network and broadcast addresses. /31 has 2 point-to-point addresses; /32 is a single host. IPv6 has no broadcast; total addresses are not an assignable-host guarantee.

Read the Source ↗

Verified 2026-09-10. Capacity and prefix guidance; not full cloud deployment validation.

AWS VPC

IPv4 /16–/28: first 4 and last address reserved. IPv6 /44–/64 in steps of 4: first 4 and last address reserved. BYOIP exceptions and service quotas are outside this profile.

Read the Source ↗

Verified 2026-09-10. Capacity and prefix guidance; not full cloud deployment validation.

Azure VNet

IPv4 /2–/29: first 4 and last address reserved. IPv6 subnets must be /64. Service-specific subnet sizes and deployment restrictions still apply.

Read the Source ↗

Verified 2026-09-10. Capacity and prefix guidance; not full cloud deployment validation.

Google Cloud · Primary

IPv4 /4–/29: first 2 and last 2 addresses reserved. IPv6 subnets are /64, with /96 interface allocations. Internal IPv6 reserves the first and last /96; external space is split into /65 halves for VMs and forwarding rules. Restricted address ranges still apply.

Read the Source ↗

Verified 2026-09-10. Capacity and prefix guidance; not full cloud deployment validation.

Google Cloud · Secondary IPv4

IPv4 secondary ranges use /4–/29, with no reserved addresses and no virtual gateway. Restricted address ranges and service-specific requirements still apply.

Read the Source ↗

Verified 2026-09-10. Capacity and prefix guidance; not full cloud deployment validation.

IPv4 /31 & /32

A /31 point-to-point link has 2 usable addresses under RFC 3021. A /32 represents one host. Host-count planning defaults to LAN subnets; request these prefixes explicitly when needed.

IPv6 Addressing & SLAAC

IPv6 has no broadcast address. A /64 is the normal LAN boundary for SLAAC. The size of a block is not a promise that every address can be assigned: subnet-router anycast and platform rules matter. /127 is used for point-to-point links and /128 for individual addresses.

IPv6 Addressing Architecture ↗

Private, Shared & Documentation Space

Private IPv4: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. Shared CGNAT: 100.64.0.0/10. IPv6 unique-local: fc00::/7; link-local: fe80::/10. Use documentation prefixes for examples. Classification describes address space, not actual reachability or routing.

DNS & Reverse Delegation

IPv4 PTR names reverse the four octets under in-addr.arpa. IPv6 reverses all 32 hexadecimal nibbles under ip6.arpa. Network delegation is simplest on octet boundaries for IPv4 and nibble boundaries for IPv6. DNS names and resolver addresses in plans are metadata; a missing DNS record does not prove an address is unused.

Browser Integration

Requires a browser that supports WebMCP.

Compatible assistants can read the active plan, calculate subnets and stage previews. Review and apply allocation changes in the planner.

Prefix Length, Block Size & Usable Hosts

IPv4 has 32 address bits and IPv6 has 128. A prefix of length p leaves 32 − p or 128 − p host bits; the full block contains two raised to that number of addresses. Increasing the prefix length by one halves the block size.

For standard IPv4 LANs through /30, subtract network and broadcast addresses to get usable capacity. An explicit /31 point-to-point link uses both addresses under RFC 3021, and /32 identifies one address. Cloud reservations are different: consult the cloud subnet comparison.

IPv6 does not have an IPv4-style broadcast address. A /64 is the usual subnet size for SLAAC; a /127 has a different point-to-point use. An exact address count is not an interface-capacity recommendation.

Put the Reference to Work

Use the calculator for boundaries and notation, the planner for capacity requirements, or range tools for exact coverage. The tables above can be expanded for all prefixes.