user@netcalc ~/calc $
ipv4_calculator
Calculate network, broadcast, mask, hosts, class and binary for any IPv4 address
ip:
mask:
✓ stdout — ipv4_calculator
Enter runs the calculation · Shift+Enter inserts a new line
user@netcalc ~/calc $
ipv6_calculator
Calculate network info for IPv6 addresses in CIDR notation
ipv6:
pfx:
✓ stdout — ipv6_calculator
user@netcalc ~/calc $
vlsm_calculator
Variable Length Subnet Mask — assigns optimal blocks for each network segment
net:
pfx:
// Subnets required
name:
hosts:
name:
hosts:
name:
hosts:
✓ stdout — vlsm_calculator
| # | Name | Hosts Req | Hosts Avail | Prefix | Network | First Host | Last Host | Broadcast | Mask |
|---|
user@netcalc ~/calc $
usable_ip_range
Shows the exact usable host range for a given network
ip:
mask:
✓ stdout — usable_ip_range
user@netcalc ~/calc $
binary_ip_calc
Convert IP addresses to binary and vice versa, with per-octet visualization
dec:
bin:
✓ stdout — binary_ip_calc
user@netcalc ~/network $
cidr_converter
Convert between CIDR, decimal mask and wildcard. Includes full /1–/32 reference table.
in:
✓ stdout — cidr_converter
📋 CIDR Reference Table
| CIDR | Subnet Mask | Wildcard | Hosts | /24 subnets | Block |
|---|
user@netcalc ~/network $
wildcard_mask_calc
Calculate the wildcard (inverse) mask for Cisco ACLs, OSPF and firewall rules
mask:
✓ stdout — wildcard_mask_calc
user@netcalc ~/network $
supernet_calculator
Find the minimum supernet containing all specified networks (route summarization)
nets:
✓ stdout — supernet_calculator
user@netcalc ~/network $
subnet_splitter
Split a network into equal subnets by specifying a new prefix
net:
mask:
new:
✓ stdout — subnet_splitter
| # | Network | First Host | Last Host | Broadcast | Hosts | Mask |
|---|
user@netcalc ~/network $
range_to_cidr
Convert an IP range (start–end) to the minimum set of CIDR blocks
start:
end:
✓ stdout — range_to_cidr
| # | CIDR Block | Network | Broadcast | Hosts |
|---|
user@netcalc ~/network $
ip_to_integer
Convert IPv4/IPv6 addresses to integer and vice versa
ip:
int:
✓ stdout — ip_to_integer
user@netcalc ~/network $
ipv6_normalize
Expand and compress IPv6 addresses — normalize any valid format
ipv6:
✓ stdout — ipv6_normalize
user@netcalc ~/network $
hex_ip_converter
Convert between hexadecimal and IP address — useful for Windows route tables and Cisco logs
ip:
0x:
✓ stdout — hex_ip_converter
user@netcalc ~/network $
vlan_calculator
802.1Q VLAN info: tag encoding, PCP, DEI, VID, range and compatibility
vlan:
pcp:
dei:
✓ stdout — vlan_calculator
user@netcalc ~/dns $
reverse_dns_generator
Generate the PTR in-addr.arpa zone for an IPv4 network
net:
pfx:
dom:
✓ stdout — reverse_dns_generator
user@netcalc ~/dns $
ipv6_ptr_generator
Generate the PTR ip6.arpa record for an IPv6 address
ipv6:
host:
✓ stdout — ipv6_ptr_generator
user@netcalc ~/dns $
ip_geolocation
Locate a public IP or resolve a domain and geolocate its public address
Domains are resolved through DNS first; geolocation is based on the resulting public IP.
geo:
✓ stdout — ip_geolocation
user@netcalc ~/dns $
ip_address_planner
Interactive IP address space planner — click cells to edit, export to CSV
📋 IP Address Plan
| # | Name | Network | Mask/CIDR | Gateway | VLAN | Location | Notes |
|---|
user@netcalc ~/legal $
Privacy
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Performance metrics
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GeoIP
Only GeoIP lookups are processed by an external provider. The requested IP address is sent for that lookup.
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This page provides operational information; it is not a legal-compliance certification.
IPv6 prefix planning without IPv4 habits
Design a simple site and VLAN hierarchy from a larger IPv6 allocation while keeping room for growth.
01
Start with hierarchy, not scarcity
IPv6 planning is usually easier when the allocation is divided by site, function and VLAN using readable hexadecimal boundaries. The goal is operational structure and summarization rather than squeezing every address.
02
Keep LANs on sensible boundaries
/64 remains the normal subnet size for general IPv6 LANs. A larger allocation such as /48 or /56 gives room to assign many /64s while still encoding site or service information into the subnet identifier.
03
Reserve space before you need it
Leave gaps between major blocks so future VLANs, additional sites or services can be added without destroying summarization. Sequentially packing every subnet tightly recreates an IPv4 habit that IPv6 was designed to avoid.
04
Document prefix purpose and routing boundary
Record which prefixes are globally routed, which are internal, where they aggregate and whether ULA is being used. A clean prefix plan should make routing policy easier to read.
05
Create a bit plan that humans can read
Decide which hexadecimal nibbles represent region, site and function. Aligning boundaries on groups of four bits makes prefixes easier to recognize in routing tables and logs, and avoids a plan where every subnet requires a calculator just to understand its ownership.
06
Aggregate at real routing boundaries
Give each site or aggregation domain a block that can be summarized upstream. Internal VLAN /64s can then change without leaking many specifics into the core. The addressing hierarchy should mirror the routing hierarchy closely enough to make summarization natural.
07
Plan addressing behavior as well as prefixes
A /64 tells you the subnet size but not whether hosts use SLAAC, DHCPv6, stable privacy addresses or manually assigned infrastructure IDs. Document router advertisements, DNS strategy and address-generation policy beside the prefix plan.
EX
Worked example
- Start with 2001:db8:1200::/48 for an organization.
- Reserve /56 blocks by site, for example 2001:db8:1200::/56 for Site 0 and 2001:db8:1200:100::/56 for Site 1.
- Inside each site assign /64s by VLAN or function, leaving hexadecimal gaps for growth.
- Advertise the /56 summary toward the core instead of every individual VLAN route where the topology allows it.
✓
Operational checklist
- Define region/site/function bits before allocating VLANs.
- Keep ordinary LANs on /64 unless a specific standard says otherwise.
- Reserve gaps and aggregation blocks deliberately.
- Document RA, SLAAC/DHCPv6 and DNS behavior with each subnet class.
Tools to apply it
Standards and references
🕐 History