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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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.
MAC randomization, OUI lookup and vendor identification
Understand why a valid MAC may not reveal a vendor and how 24-, 28- and 36-bit IEEE assignments differ.
01
Vendor lookup begins with an assigned prefix
Traditional vendor identification compares the leading MAC bits with IEEE registration blocks. MA-L, MA-M and MA-S assignments can use different prefix lengths, which is why a modern database should not stop at a 24-bit OUI.
02
Locally administered addresses change the interpretation
A locally administered bit indicates that the address was not necessarily assigned globally by the hardware vendor. Operating systems commonly use randomized addresses for Wi-Fi privacy, so a syntactically valid MAC can have no meaningful vendor match.
03
Randomization is expected behavior
Private Wi-Fi addresses reduce passive tracking between networks. Seeing a changing or unknown MAC on a client device is therefore not automatically evidence of spoofing or a faulty OUI database.
04
Use vendor data as context, not identity
Even a valid IEEE match identifies the registered organization for a prefix, not necessarily the product model, current owner or device purpose.
05
Read the U/L bit before trusting a vendor result
The locally administered bit in the first octet is a strong clue that the address may be software-selected rather than globally assigned by an IEEE registration block. Privacy addresses can therefore look perfectly valid while intentionally avoiding stable vendor identity.
06
Prefer the most specific registered prefix
Modern IEEE assignments are not all 24 bits. A lookup implementation should test longer registered prefixes where available before falling back to shorter ones, otherwise a broad organization block can hide a more specific assignment.
07
Interpret vendor matches conservatively
A prefix match can help identify likely equipment families in inventory or packet captures, but virtual NICs, OEM relationships, reused modules and manually assigned addresses limit certainty. Treat the result as evidence for classification, not authentication.
EX
Worked example
- Normalize 00:50:56:AA:BB:CC into a canonical hexadecimal form before lookup.
- Check whether the locally administered bit is set; if it is, warn that vendor attribution may be meaningless.
- Search the local IEEE-derived database from the most specific registered prefix toward broader assignments.
- Present the organization match together with the prefix length so the user can judge confidence.
✓
Operational checklist
- Normalize the MAC before matching.
- Check the locally administered bit.
- Prefer MA-S/MA-M specificity where registered before broad MA-L matches.
- Never use a vendor prefix as proof of device identity.
Tools to apply it
Standards and references
🕐 History