Kernaali ToolsIPv4 Subnet Calculator
Find the network, broadcast, mask and usable address range for an IPv4 prefix.
Calculator / generatorNetwork calculators, configuration generators and cheat sheets.
Plan a subnet. Compare network lists. Prepare a firewall change.
Calculations stay in your browser. No accounts, ads or tracking scripts.
80 tools and references
No matching tools
Try a shorter task name or clear the filters to see the full directory.
Featured tools
Address planning
CIDR to Netmask Converter
Convert an IPv4 prefix length into a contiguous dotted-decimal subnet mask.
Calculator / generatorNetmask to CIDR Converter
Validate an IPv4 subnet mask and recover its prefix length.
Calculator / generatorWildcard Mask Calculator
Convert between a contiguous subnet mask and its inverse ACL wildcard.
Calculator / generatorIP Range to CIDR Converter
Cover an inclusive IPv4 range with the smallest exact set of CIDR blocks.
Calculator / generatorCIDR Aggregation & Route Summarization Calculator
Aggregate IPv4 or IPv6 CIDRs exactly, or calculate a covering supernet with explicit counts of extra address space.
Calculator / generatorSubnet Splitter
Divide one IPv4 parent network into equal-size child subnets.
Calculator / generatorVLSM Calculator
Allocate different-size IPv4 LAN subnets from a parent network.
Calculator / generatorIPv6 Subnet Calculator
Calculate an IPv6 network boundary, final address and exact address-space size.
Calculator / generatorIPv6 Address Expander and Compressor
Normalize IPv6 text and inspect all eight hexadecimal groups.
Calculator / generatorReverse DNS / PTR Converter
Build IPv4 host reverse names and IPv6 host or nibble-aligned reverse-zone names.
Calculator / generatorCIDR List Comparison & Overlap Checker
Compare two IPv4 or IPv6 CIDR lists and get their exact intersection, differences, duplicates and containment relationships.
Calculator / generatorLink & transport
TCP MSS Calculator
Find the TCP MSS option value for an IP MTU, and the room left for TCP data when options are present.
Calculator / generatorMTU Budget Calculator
Find the inner IP packet size and ping data size that fit after reserving bytes for tunnel headers.
Calculator / generatorIPsec / ESP Overhead Calculator
Find how many bytes IPsec adds to your packet and the resulting IP packet size.
Calculator / generatorBandwidth and Transfer Time Calculator
Estimate file transfer duration with explicit file units and useful-throughput efficiency.
Calculator / generatorBandwidth-Delay Product Calculator
Estimate bytes in flight from bottleneck bandwidth and round-trip delay.
Calculator / generatorPackets Per Second / Line Rate Calculator
Find the Ethernet frames per second that fit a link rate, including the time used by preamble and the gap between frames.
Calculator / generatorFiber Optic Link Budget Calculator
Estimate optical path loss and spare margin from your transceiver and cable specifications.
Calculator / generatordBm / mW Converter
Convert logarithmic power in dBm to milliwatts and back.
Calculator / generatorVLAN / Ethernet Frame Overhead Calculator
Calculate Ethernet frame size, tag cost, padding and payload efficiency.
Calculator / generatorConfiguration & sysadmin
FortiGate Bulk Address Object Generator
Generate FortiOS address objects from IPv4 lists or name,cidr CSV, preview the batch, and copy or download the CLI configuration.
Calculator / generatorFortiGate Address Group Generator
Create an IPv4 address group snippet from existing object names.
Calculator / generatorFortiGate Service Object Generator
Generate a TCP or UDP destination-port service object for FortiOS.
Calculator / generatorIKEv2 Proposal Checker
Check whether selected IKEv2 encryption and integrity choices fit together, and identify the setting to change.
Calculator / generatorchmod Permission Calculator
Translate a three-digit Unix octal mode into owner, group and other permissions.
Calculator / generatorReferences
IPv4 Subnet Mask Table
One A4 page: every IPv4 prefix, mask, wildcard, address count, subnet boundaries and special-range reminders.
A4 referenceSubnetting Worked Examples
Work through original subnetting examples for boundaries, host capacity and address allocation.
A4 referenceSpecial and Private IP Address Reference
Recognize common private, shared, loopback, documentation and local address ranges.
A4 referenceCommon TCP / UDP Ports Reference
Common service ports and transport choices in a printable reference.
A4 referenceDNS Record Cheat Sheet
Understand common DNS record types, TTLs and frequent configuration mistakes.
A4 referenceIPv6 Quick Reference
A one-page A4 reference for IPv6 notation, prefix sizes, address types, multicast and reverse DNS.
A4 referenceEthernet, MTU & TCP MSS Quick Reference
A one-page A4 reference for frame size, VLAN overhead, IP MTU, TCP MSS and tunnel budgeting.
A4 referenceWi-Fi PHY Rate & Channel Width Cheat Sheet
One A4 page explaining Wi-Fi generations, channel widths, spatial streams and PHY rates without promising Internet speeds.
A4 referenceMikroTik
MikroTik RouterOS WiFi Band Quick Reference
One A4 page of current /interface/wifi band selectors, package distinctions and channel-width syntax.
A4 referenceMikroTik LTE & 5G Band Quick Reference
One A4 field reference for selected European-relevant LTE and NR bands, duplex modes, frequency ranges and RouterOS selectors.
A4 referenceMikroTik RouterOS 7 Basic Internet Setup
Build a wired WAN-to-LAN setup with DHCP, a bridge, DNS, masquerade and explicit firewall protection.
Practical guideMikroTik Port Forward Works Externally but Fails from LAN
Fix same-subnet hairpin NAT with a LAN destination rule and a scoped return-path translation; check external forwarding separately.
Practical guideMikroTik RouterOS 7 Firewall Basics
Allow LAN Internet access, restrict SSH and WinBox to one administrator, and apply separate IPv4 and IPv6 firewall rules.
Practical guideMikroTik Bridge VLAN Filtering Without Losing Management
Stage RouterOS bridge VLANs and diagnose a management lockout: CPU-port membership, PVID, tagged uplinks, input policy and Safe Mode recovery.
Practical guideMikroTik WiFi Command Not Found: wifi or wireless?
Fix commands copied for the wrong wireless driver and set a supported channel width in the correct RouterOS menu.
Practical guideMikroTik LTE/5G: Choose or Clear a Band, Cell or Operator Lock
Choose the correct LTE/5G restriction and undo a band, cell or operator lock without confusing the three settings.
Practical guideMikroTik LTE & 5G NR Band Locking
Select or restore LTE and NR bands with supported RouterOS properties while accounting for carrier aggregation and NSA anchors.
Practical guideMikroTik LTE: Find EARFCN and Cell ID for a Cell Lock
Read the serving LTE cell, scan supported modems and collect the EARFCN/PCI pair needed for cell locking.
Practical guideMikroTik LTE Cell Lock: Modem-Specific Commands
Choose the documented LTE cell-lock family, query supported locks and understand reset, handover and carrier-aggregation limits.
Practical guideMikroTik 5G SA Cell Lock: Support & Limits
Lock a supported modem to a measured 5G SA cell, query or clear the lock, and avoid applying it to an NSA connection.
Practical guideMikroTik LTE / 5G Troubleshooting
Fix an ignored manual APN on an MBIM modem, restore registration after a bad lock, or separate LTE service from LAN forwarding.
Practical guideMikroTik Common Problems and Fixes
Find the fix for client DNS, hairpin NAT, lost VLAN management, FastTrack, WireGuard, LTE APN and device-mode errors.
Practical guideMikroTik Hardware Offload Missing or Firewall Rules Bypassed
Check model and port-group limits when H is missing, routing loads the CPU, or full L3 hardware offload bypasses firewall rules.
Practical guideMikroTik FastTrack Bypasses Queues or Policy Routing
Diagnose simple queues that do not limit traffic, missing packet marks and connections taking the wrong WAN when FastTrack is enabled.
Practical guideMikroTik WireGuard Handshake but No Traffic
Trace allowed-address, routes, input versus forward rules and the return path when a RouterOS WireGuard peer handshakes but cannot reach the remote LAN.
Practical guideMikroTik DHCP Relay Uses the Wrong Source IP
Use local-address-as-src-ip on RouterOS 7.17+ when the DHCP server path expects the relay address instead of the transit source.
Practical guideMikroTik DNS Works on the Router but Not on Clients
Check DHCP-advertised DNS, allow-remote-requests, TCP and UDP 53, static records and application DNS when RouterOS resolves names but LAN clients fail.
Practical guideMikroTik WireGuard Stops After a Mobile IP Change
Compare endpoint-address and current-endpoint-address, NAT keepalive and responder roles after an LTE/5G or roaming endpoint changes.
Practical guideMikroTik “DoH server connection error”: DNS over HTTPS Checks
Diagnose resolving error, SSL errors and connection reset by peer using DoH bootstrap DNS, endpoint compatibility and certificate validation.
Practical guideMikroTik “failure: not allowed by device-mode”
Find the device-mode setting for the refused RouterOS tool, then enable the sniffer with physical confirmation. Handle flagged configuration separately.
Practical guideMikroTik WireGuard Import: “Could not parse”
Fix a RouterOS WireGuard import rejected because the configuration file begins with a comment.
Practical guideUniFi
UniFi WiFi Problems: IoT Connection, Slow Speed and Roaming Fixes
Fix legacy IoT connection failures, congested channels, unintended speed limits and poor client coverage with the relevant UniFi setting.
Practical guideUniFi VLAN SSID Not Getting an IP Address
Configure the SSID VLAN and trace missing DHCP through AP native/tagged ports, switch uplinks and the gateway while preserving AP management.
Practical guideUniFi Guest Isolation Not Blocking Local Devices
Block Guest access across VLANs and between clients on the same VLAN, while keeping intentional Trusted-to-IoT exceptions.
Practical guideUniFi: Allow One Trusted-to-IoT Service and Block the Rest
Create a specific trusted-to-IoT service allowance, order stateful replies and blocks, and keep gateway services separate.
Practical guideUniFi Port Forwarding Not Working: NAT and Return-Path Checks
Trace failed UniFi port forwards through CGNAT or double NAT, WAN selection, the server listener and the return route.
Practical guideUniFi Adoption Failed or Stuck Adopting
Check Network application compatibility, management VLAN, TCP 8080 reachability and previous management before resetting an AP or switch.
Practical guideUniFi Duplicate IP Address or Rogue DHCP Warning
Investigate “Multiple devices are using the same IP address”, static addresses inside DHCP pools and DHCP Guarding without blocking the legitimate server.
Practical guideUniFi AP Reboots or Goes Offline: PoE and Uplink Checks
Use AP uptime, PoE events and link changes to distinguish power loss, cable faults and management connectivity failures.
Practical guideUniFi mDNS: AirPrint or AirPlay Missing Across VLANs
Separate service discovery from the application connection, scope the mDNS proxy and diagnose IoT discovery without opening every inter-VLAN service.
Practical guideUniFi STP Blocked Port or Network Loop Warning
Distinguish normal RSTP redundancy from Loop Protection or BPDU Guard shutdown, inspect wired and mesh paths, and recover without disabling loop protection globally.
Practical guideUniFi Ethernet Uplink Stuck at 100 Mbps
Diagnose FE instead of GbE on an AP, switch or gateway: verify negotiated speed, isolate cable and port faults, and separate link rate from Wi-Fi throughput.
Practical guideFortiGate
FortiGate IKEv1 to IKEv2 Site-to-Site Migration
Convert an existing route-based FortiGate tunnel to IKEv2: phase 1 changes, peer IDs, Child SA selectors and common negotiation failures.
Practical guideFortiGate IKE Debug Shows No Output
Check VDOM, inherited filters, log-filter versus log filter syntax and whether a negotiation is actually starting.
Practical guideFortiGate IPsec Up but a New Subnet Has No Traffic
Trace one new protected network through Child SA selectors, routing, policy, NAT and the destination host’s return path.
Practical guideFortiGate Local-In Policy: Management Access and Rule Order
Troubleshoot FortiGate management access using interface services, trusted hosts and local-in rule order, with a scoped CLI example.
Practical guideFortiGate Conserve Mode During FortiGuard Updates
Apply Fortinet’s scoped IPS-update memory workaround on 2 GB models and identify the related fixed high-CPU defect.
Practical guideFortiGate Policy Routing Between VDOMs Fails RPF
Fix an inter-VDOM policy-routing RPF drop when a suitable kernel return route cannot be used, with an exception on the receiving VDOM link.
Practical guideFortiGate Config Migration: Interface Mapping and Import Errors
Troubleshoot cross-model FortiGate imports with config-error-log, interface dependency mapping and a comparison of the loaded configuration.
Practical guideFortiGate “no proposal chosen”: IKE, ESP and DH Checks
Troubleshoot FortiGate proposal errors by tunnel selection, IKE/ESP transforms, PRF, DH, PFS and the failed negotiation stage.
Practical guideFortiClient IKEv2 Migration: Enable EAP and Restore User Groups
Fix the PSK/local-user migration settings: enable EAP, restore policy groups and remove the conflicting tunnel-level group binding.
Practical guideFortiGate IPsec with Overlapping Subnets: NAT and Selectors
Map overlapping VPN networks to distinct translated prefixes and align FortiGate selectors, routes, IP pools, VIPs and reverse traffic.
Practical guideFortiGate IPsec Tunnel Up but Traffic Stops Intermittently
Diagnose intermittent IPsec data loss using Child SA rekey, tunnel counters, routing and narrowly scoped hardware-offload issues.
Practical guideFortiGate Cannot Delete an Interface or Its Address Object
Remove an automatically created interface-subnet object or an obsolete packet-capture reference using the documented correction.
Practical guideA quick subnet example
10.42.7.93/26 belongs to 10.42.7.64/26. Its usable range is 10.42.7.65–10.42.7.126: 62 addresses. Open the subnet calculator to inspect the mask and broadcast address.