Network and platform guides

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131 entries

IPv4 Subnet Mask Table

One A4 page: every IPv4 prefix, mask, wildcard, address count, subnet boundaries and special-range reminders.

Subnetting Worked Examples

Work through original subnetting examples for boundaries, host capacity and address allocation.

Special and Private IP Address Reference

Recognize common private, shared, loopback, documentation and local address ranges.

Common TCP / UDP Ports Reference

Common service ports and transport choices in a printable reference.

DNS Record Cheat Sheet

Understand common DNS record types, TTLs and frequent configuration mistakes.

IPv6 Quick Reference

A one-page A4 reference for IPv6 notation, prefix sizes, address types, multicast and reverse DNS.

Ethernet, MTU & TCP MSS Quick Reference

A one-page A4 reference for frame size, VLAN overhead, IP MTU, TCP MSS and tunnel budgeting.

Wi-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.

MikroTik RouterOS WiFi Band Quick Reference

One A4 page of current /interface/wifi band selectors, package distinctions and channel-width syntax.

MikroTik LTE & 5G Band Quick Reference

One A4 field reference for selected European-relevant LTE and NR bands, duplex modes, frequency ranges and RouterOS selectors.

MikroTik RouterOS 7 Basic Internet Setup

Build a wired WAN-to-LAN setup with DHCP, a bridge, DNS, masquerade and explicit firewall protection.

MikroTik 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.

MikroTik RouterOS 7 Firewall Basics

Allow LAN Internet access, restrict SSH and WinBox to one administrator, and apply separate IPv4 and IPv6 firewall rules.

MikroTik 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.

MikroTik 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.

MikroTik 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.

MikroTik LTE & 5G NR Band Locking

Select or restore LTE and NR bands with supported RouterOS properties while accounting for carrier aggregation and NSA anchors.

MikroTik 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.

MikroTik LTE Cell Lock: Modem-Specific Commands

Choose the documented LTE cell-lock family, query supported locks and understand reset, handover and carrier-aggregation limits.

MikroTik 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.

MikroTik 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.

MikroTik Common Problems and Fixes

Find the fix for client DNS, hairpin NAT, lost VLAN management, FastTrack, WireGuard, LTE APN and device-mode errors.

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.

UniFi 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.

UniFi 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.

UniFi: 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.

UniFi 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.

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.

FortiGate IKE Debug Shows No Output

Check VDOM, inherited filters, log-filter versus log filter syntax and whether a negotiation is actually starting.

FortiGate 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.

FortiGate 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.

FortiGate 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.

MikroTik 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.

MikroTik 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.

MikroTik 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.

MikroTik 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.

MikroTik 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.

UniFi Adoption Failed or Stuck Adopting

Check Network application compatibility, management VLAN, TCP 8080 reachability and previous management before resetting an AP or switch.

UniFi 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.

UniFi 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.

UniFi 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.

UniFi 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.

FortiGate 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.

FortiGate 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.

FortiGate “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.

FortiClient 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.

MikroTik 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.

MikroTik “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.

MikroTik “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.

FortiGate 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.

FortiGate 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.

UniFi 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.

MikroTik WireGuard Import: “Could not parse”

Fix a RouterOS WireGuard import rejected because the configuration file begins with a comment.

FortiGate 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.

FortiGate Hardware Offload Problems: NPU/ASIC Fixes and Workarounds

Traffic works until FortiGate offloads it? Find scoped NPU/ASIC fixes for IPsec, QinQ, NP6 failback and SoC5 shaping, with CLI commands and fixed releases.

FortiGate SSL VPN Support Matrix by Model and FortiOS Version

Check which FortiGate models still support FortiClient SSL VPN, the last working FortiOS version, upgrade cutoffs, and where Agentless VPN remains.

Mac Connected to Wi-Fi but No Internet

Mac Wi-Fi connected but websites won't load? Check DHCP, router, DNS and VPN separately before resetting network settings.

Mac VPN Connected but Internet or DNS Fails

Troubleshoot Mac VPN connections that break internet access, internal DNS or local network resources. Understand split tunneling and routing.

Mac External Monitor Not Detected

Fix a MacBook external display that stays black or runs at the wrong resolution. Check USB-C video support, docks, detection and Mac limits.

iPhone Personal Hotspot Not Working

Can't find or join an iPhone hotspot? Check cellular data, Allow Others to Join, compatibility, Wi-Fi passwords and USB connection.

iPhone Private Wi-Fi Address: Off, Fixed or Rotating?

Understand iPhone Private Wi-Fi Address settings and why MAC-based access lists, reservations or guest networks may behave differently.

AirDrop Not Working on iPhone or Mac

Troubleshoot AirDrop when a nearby iPhone or Mac doesn't appear, requests fail or receiving settings prevent transfers.

MacBook Battery Health, Cycle Count and Charging

Find MacBook battery cycle count, interpret battery health and charging limits, and troubleshoot slow or interrupted charging.

FortiGate packet capture commands and useful filters

Capture one FortiGate traffic flow with bounded sniffer commands. Find ingress, egress and replies, account for NAT, and stop captures safely.

FortiGate debug flow commands: filter, capture and stop

Run a bounded FortiGate debug flow for one connection. Understand policy, route and session messages, then stop debugging and clear filters.

FortiGate session table commands for policy and NAT checks

Filter FortiGate sessions by client, destination and port. Read policy IDs, NAT actions and reply counters without clearing live connections.

FortiGate route lookup and policy route commands

Check the route to a destination and match a complete flow against FortiGate policy routing. Separate route availability from forwarding decisions.

FortiGate BGP commands for neighbors and route verification

Check FortiGate BGP state, accepted and advertised routes, and routing-table installation. Diagnose one peer without resetting the BGP session.

FortiGate interface, ARP and error counter commands

Inspect FortiGate link state, interface counters and ARP resolution. Compare counter changes and separate physical faults from Layer 3 problems.

FortiGate HA status and configuration synchronization commands

Inspect FortiGate FGCP members, roles and configuration checksums. Localize a synchronization mismatch without forcing failover or resynchronization.

FortiGate SD-WAN diagnostic commands for members, SLA and rules

Check FortiGate SD-WAN health, members and rule selection. Use the right service command for your FortiOS version and verify the actual flow.

FortiGate DNS cache and NTP diagnostic commands

Inspect FortiGate FQDN resolution and NTP synchronization. Distinguish cached addresses, DNS reachability, clock offset and time-zone display.

FortiGate and FAC commands for IKEv2 MFA troubleshooting

Correlate FortiGate IKE and RADIUS authentication with FAC push approval. Capture one login, identify timeout boundaries and stop debugging cleanly.

MikroTik Ethernet Commands: Link, Errors and SFP Status

Read RouterOS Ethernet link speed, errors, traffic counters and SFP diagnostics with a focused command reference and an evidence-first workflow.

MikroTik Bridge Commands: MAC Table, Ports and VLANs

Find a MAC address on a RouterOS bridge and inspect VLAN membership, PVID and hardware-offload state without changing the bridge configuration.

MikroTik Route Commands: Routing Tables and Policy Rules

Inspect RouterOS v7 routes, next hops, custom tables and policy rules. Separate a missing route from selection of the wrong routing table.

MikroTik Firewall Commands: Counters and Connections

Inspect RouterOS firewall counters, NAT rules and connection tracking to follow one connection without flushing sessions or adding broad allow rules.

MikroTik Torch and Packet Sniffer Commands

Choose Torch or the RouterOS packet sniffer, filter one host or service, and understand NAT, hardware-offload and FastTrack visibility limits.

MikroTik DHCP Commands: Leases, Pools and Options

Find RouterOS DHCP leases, check pool use and inspect delivered network settings. Separate server, client and relay questions before changing leases.

MikroTik BGP Commands: Sessions, Prefixes and Routes

Inspect RouterOS v7 BGP session state and one received prefix. Separate session establishment, route acceptance and next-hop selection.

MikroTik OSPF Commands: Neighbours, Interfaces and LSAs

Read RouterOS v7 OSPF neighbour states, interface templates and LSAs. Check adjacency and route installation as separate troubleshooting stages.

MikroTik Backup, Export and Safe Mode Commands

Choose RouterOS binary backup or readable export, protect sensitive files and use Safe Mode for small remote changes without confusing it with a backup.

MikroTik IPsec Commands: Peers, Policies and SA Counters

Inspect RouterOS IPsec IKE peers, matching policies and selected SA counters while avoiding session resets and accidental exposure of encryption keys.

Junos Interface Errors and Optical Power Commands

Check Juniper link state, interface errors, flaps and optical receive power. A practical read-only workflow for MX, with EX and SRX differences.

Junos Route Lookup and VRF Routing Table Commands

Find IPv4 and IPv6 routes in Junos inet.0 and VRF tables. Compare a destination lookup, an exact prefix and the Routing Engine forwarding table.

Junos BGP Troubleshooting: Neighbors and Advertised Routes

Troubleshoot Juniper BGP state, received routes and advertised prefixes. Understand what each command proves before resetting a session.

Junos OSPF Troubleshooting Commands and Neighbor States

Check Junos OSPF neighbors, interface timers, MTU and learned routes. Distinguish normal 2-Way behavior from a failed adjacency.

Junos IS-IS Commands: Adjacencies, Levels and Metrics

Inspect IS-IS neighbors, Level 1 and Level 2 operation, interface metrics and the database on Juniper MX without resetting the protocol.

Junos LLDP, ARP and MAC Address Lookup Commands

Trace an endpoint from IP to MAC to switch port. Separate Juniper EX ELS switching commands from MX bridge-domain commands.

Junos Firewall Filter Counters and Packet-Drop Checks

Inspect Junos stateless firewall filters, counters and policers. Verify attachment and compare counter changes without clearing production evidence.

Junos Compare, Commit Confirmed and Rollback Reference

Review a Junos candidate, validate syntax and use commit confirmed deliberately. Understand rollback 0 versus rollback 1 before changing a device.

Junos LACP Troubleshooting and AE Member Commands

Check Juniper LACP actor and partner state, packet counters and aggregate members. Diagnose a missing link without bouncing the whole bundle.

Junos Logs, NTP and System Health Commands

Collect Juniper logs, current time, NTP peer state and alarms before troubleshooting. Build a reliable incident timeline with read-only commands.

Cisco IOS XE Interface Commands: Status, Errors and Drops

Check Cisco IOS XE interface status, CRC errors, drops and err-disabled ports. Read-only Catalyst commands with a practical troubleshooting workflow.

Cisco VLAN and Trunk Show Commands: Find the Missing VLAN

Troubleshoot Cisco Catalyst VLANs and 802.1Q trunks with read-only IOS XE commands. Compare allowed, active and forwarding VLANs at both ends.

Cisco Spanning Tree Commands: Root, Blocking and Inconsistent Ports

Find the STP root, inspect blocked ports and investigate inconsistent states on Cisco IOS XE. Includes separate PVST and MST read-only workflows.

Cisco EtherChannel and LACP Commands: Check Bundles and Members

Check Cisco IOS XE port-channel status, LACP neighbors and member flags. Understand suspended links and uneven traffic without resetting the bundle.

Find a Device on a Cisco Switch: CDP, LLDP, ARP and MAC Commands

Trace an IP address to a Cisco switch port using ARP, MAC tables, CDP and LLDP. Learn which table to check and where the method stops working.

Cisco IOS XE Route Lookup: Routing Table, VRF and CEF Commands

Look up an IPv4 route in Cisco IOS XE, select the correct VRF and inspect CEF forwarding. Separate routing-table evidence from end-to-end reachability.

Cisco IOS XE BGP Commands: Neighbors, Prefixes and Advertisements

Check IOS XE BGP sessions, accepted prefixes, advertised routes and route installation. Read-only commands with practical interpretation and scope limits.

Cisco OSPF Show Commands: Neighbors, Interfaces and Missing Routes

Troubleshoot OSPFv2 on IOS XE using neighbor, interface and database commands. Understand 2-Way, ExStart and Full without resetting the process.

Cisco ACL Counters: Verify Rules, Direction and Hardware Drops

Check IOS XE IPv4 ACL attachment and rule matches. Learn why zero software counters on Catalyst 9000 do not prove that hardware traffic missed an ACL.

Cisco IOS XE NAT Commands: Translations, Statistics and Troubleshooting

Inspect IOS XE IPv4 NAT translations and statistics without clearing sessions. Follow a single flow and distinguish NAT state from successful connectivity.

UniFi SSH Commands: Console, AP and Switch Diagnostics

Find the right UniFi SSH credentials and collect read-only device logs. Separate console, AP and switch access from legacy USG and EdgeOS commands.

UniFi Packet Capture: Where to Capture and What to Filter

Choose a useful UniFi capture point for DHCP, DNS and TCP failures. Run short tcpdump captures and distinguish missing packets from a wrong interface.

UniFi Management Ports: Device, Server and Admin Traffic

Understand key UniFi management ports by endpoint and purpose. Separate device communication, browser access and discovery before changing firewall rules.

UniFi Backup vs Support File: What to Save Before a Change

Save the right UniFi backup and collect console or device support files. Build a useful incident bundle without confusing recovery data with logs.

EdgeRouter CLI Modes, Commit, Save and Commit-Confirm

Understand EdgeOS operational and configuration modes. Preview changes and use commit-confirm correctly, including its reboot and saved-config behavior.

EdgeRouter Route and BGP Show Commands

Check EdgeOS routes, BGP sessions and advertised prefixes. Separate the BGP table, active routing table and policy-routing path before changing peers.

EdgeRouter Interface and ARP Diagnostics

Inspect EdgeOS interfaces and interface MAC addresses, then capture ARP on the correct LAN. Separate a physical port from its VLAN or switch interface.

EdgeRouter Firewall and NAT Counters: Follow One Connection

Read EdgeOS firewall and NAT counters without clearing sessions. Check interface attachment, WAN_IN versus WAN_LOCAL, rule order and a fresh test connection.

tcpdump Filter Examples for Everyday Network Troubleshooting

Copy focused tcpdump filters for hosts, networks, DNS and TCP. Learn where to capture, how to save a PCAP and what missing packets really mean.

Wireshark Display Filters and Capture Filters: Practical Examples

Find practical Wireshark display filters and matching capture filters for hosts, ports, DNS and TCP. Avoid common mistakes when investigating packet loss.

dig Commands for DNS Troubleshooting

Diagnose DNS with dig: choose a resolver, compare A and AAAA answers, test TCP, inspect response codes and distinguish NXDOMAIN from an empty answer.

PowerShell Network Tests: DNS, TCP Ports and Connections

Use Test-NetConnection, Resolve-DnsName and Get-NetTCPConnection to separate DNS, route, TCP and local-listener problems on Windows.

Linux Network Troubleshooting with ip and ss

Inspect Linux addresses, route selection, neighbors and sockets with read-only ip and ss commands. Find the right interface and local listener before changing configuration.

OpenSSL Commands to Check TLS Certificates and Chains

Check a server certificate with OpenSSL while preserving SNI and hostname verification. Inspect expiry, SAN names and the difference between a supplied and trusted chain.

curl Commands for HTTP, DNS and TLS Troubleshooting

Separate DNS, TCP, TLS and HTTP failures with curl. Test one backend with --resolve, preserve hostname verification and read timing results correctly.

iperf3 Throughput Testing Without Misreading the Result

Run repeatable iperf3 tests and interpret single-stream, reverse and UDP results. Separate path capacity from endpoint limits without hiding weak performance.

BGP Neighbor States: Idle, Active, OpenSent and Established

Interpret all six BGP neighbor states, common reset reasons and an Established session with zero routes. Start with targeted read-only checks.

Optical Receive Power and CRC Errors: A Troubleshooting Checklist

Interpret SFP receive power, alarms and growing CRC counters. Compare both ends, use the actual optic limits and avoid replacing parts without evidence.

Access, Trunk, Native VLAN and PVID: What Must Match

Understand tagged and untagged VLAN traffic across vendors. Compare ingress classification, allowed membership and egress tagging before changing a port.

DHCP DORA Troubleshooting: Discover, Offer, Request and ACK

Locate a DHCPv4 failure by following Discover, Offer, Request and ACK. Use packet evidence to distinguish VLAN, relay, scope and client problems.

Network Commands Compared: FortiGate, MikroTik, Junos and Cisco

Find interface, IPv4 route and BGP inspection commands across FortiGate, MikroTik, Junos and Cisco, with context and links to detailed references.

How to Find the ASN of an IP Address

Use the most-specific observed route to find an IP address’s BGP origin, then compare that evidence with registry information.

How to Find the Prefixes Announced by an ASN

Inspect originated IPv4 and IPv6 routes without confusing them with allocations or networks reached through transit.

Upstream Providers, Peering and AS Paths Explained

Read an observed AS path without treating it as a map of commercial contracts or the packet path your application used.

Why IP WHOIS and ASN Results Can Differ

Registry records describe resource registration; BGP observations describe routing. A difference between them needs context, not an automatic error verdict.

How to Read Traceroute and MTR Results

Compare destination behavior with intermediate replies before deciding where a connection fails.

RPKI Valid, Invalid and Not Found Explained

Validate a prefix–origin pair, including its prefix length, and keep validator availability separate from the routing result.

DNS Propagation, TTL and Cached Missing Records

Compare the exact DNS question and its cached answer before treating a recent change as complete or broken.