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 $
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GeoIP
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How to design a clean DHCP scope
Plan gateways, reservations, dynamic ranges and growth capacity inside an IPv4 subnet without address collisions.
01
Separate infrastructure from dynamic clients
Reserve a documented region for gateways, switches, APs, servers and other static infrastructure before defining the dynamic pool. The exact numbering convention matters less than keeping it consistent.
02
Size for peaks and lease behavior
A subnet with enough addresses on paper can still exhaust if leases are long and transient clients accumulate. Consider normal concurrency, guest churn and growth rather than sizing only for today’s inventory.
03
Avoid overlapping reservations and pools
Static reservations, excluded addresses and the dynamic range should be easy to audit. When multiple DHCP servers or failover peers exist, make the ownership model explicit.
04
Document DNS, gateway and option intent
A DHCP scope is more than a start/end range. Record default gateway, DNS servers, domain/search options, lease time and any vendor-specific options needed by the clients.
05
Design redundancy before the first outage
If DHCP is important to the site, decide whether failover, split scopes or redundant servers are required. Redundancy design must account for who owns leases and how the secondary behaves during a partition, not simply place two independent servers on the same VLAN.
06
Monitor utilization and conflict signals
Track active leases, free addresses, decline/conflict events and lease churn. A scope that regularly exceeds roughly its expected peak capacity needs investigation before users experience intermittent “no address” failures. The useful threshold depends on churn and recovery time, not one universal percentage.
07
Protect the segment from unintended DHCP servers
Rogue or misconfigured DHCP can be more disruptive than scope exhaustion. On managed access networks, features such as DHCP snooping and trusted uplinks can limit where server replies are accepted, while logs help identify the offending port.
EX
Worked example
- For 192.168.10.0/24, reserve .1 for the gateway and an infrastructure range such as .2-.49.
- Use .50-.200 as the dynamic pool, leaving a clearly documented reserve for future static or special-purpose hosts.
- Set lease time according to client churn: a guest WLAN and a stable office LAN do not need the same policy.
- Monitor free leases and test the failover path before calling the scope finished.
✓
Operational checklist
- Separate infrastructure, reservations, dynamic pool and reserve space.
- Document gateway, DNS, lease time and special options.
- Monitor free leases and decline/conflict events.
- Prevent unauthorized DHCP replies on managed access networks.
Tools to apply it
Standards and references
🕐 History