3CX & VoIP
3CX and VoIP troubleshooting:SIP trunks, DECT, SBC, NAT, RTP, audio quality, certificates, phones and backups.
3CX / VoIP Center
3CX and VoIP Center: SIP trunks, extensions, DECT, telephones, audio, transfers, routing, ports and telephone diagnostics
ResourceSSL Center / Certificates / PKI
SSL/TLS analysis and diagnosis: expiration, SAN, certification chain, PEM, CSR, AD CS and troubleshooting commands
Knowledge hubHome
Free tools, procedures, diagnostics, scripts, dictionary and practical resources for IT technicians, system administrators and SMEs
IT dictionarySIP Trunk
A SIP trunk connects a business IP PBX, such as 3CX, to a telephony provider or another PBX over an IP network.
IT dictionary3CX
3CX is a software IP PBX for business calling, managing extensions, SIP trunks, call routing, queues and IP phones, DECT handsets or desktop and mobile apps.
IT dictionarySRTP
Secure Real-time Transport Protocol encrypts and authenticates RTP voice or video packets.
IT dictionarySIP Dialog
A SIP dialog is the persistent signaling relationship identified by Call-ID and dialog tags.
IT dictionarySIP URI
A SIP URI identifies a communication endpoint, commonly using the sip:user@domain format.
IT dictionarySIP 480 Temporarily Unavailable
SIP 480 reports that the called destination is temporarily unavailable.
ResourceHow to troubleshoot SIP 488 Not Acceptable Here
Compare SDP offers, codecs, and media settings when a trunk or endpoint rejects a call.
ResourceHow to find the address Mac of a Windows computer
Identify the physical address of an Ethernet card or Wi-Fi
Troubleshooting3CX: one-way audio on calls
A 3CX call connects but only one side hears audio. Investigate RTP/SRTP media, NAT, firewall rules, SIP ALG, SDP addresses and remote SBC paths.
Resource503 — SIP service unavailable
The SIP server or trunk is temporarily unable to process the request.
TroubleshootingA carrier trunk returns SIP 503 Service Unavailable
The remote SIP server temporarily refuses to process calls.
Resource487 — SIP request terminated
The SIP transaction was canceled, often after a CANCEL request.
Resource408 — SIP request timeout
The SIP request did not receive a final response within the expected time.
TroubleshootingCalls fail with SIP 488 Not Acceptable Here
The destination rejects the media offer or selected SDP parameters.
ProcedureRecover a Docker service stuck in a restart loop
Diagnose a Docker restart loop using logs, exit state, memory and dependency evidence while preserving volumes and the deployment configuration.
ProcedureCreate iSCSI storage with MPIO
Controlled procedure to create iscsi storage with mpio
ProcedureDeploy a new VLAN in production
Deploy a VLAN through switches, gateway and DHCP, then validate pilot connectivity, firewall segmentation and a controlled rollback.
ProcedureRenew a RADIUS / 802.1X certificate
Procedure for renewing a server certificate used by the 802.1X authentication
ProcedureAdd a new Active Directory site
Controlled procedure to add a new active site
ResourceNetwork ports — memo form
Common TCP and UDP ports, their services and practical checks for network administration.
Knowledge hubIT Networking
Tools and methods for DNS, DHCP, VLAN, routing, Wi-Fi, LINK, TITLE/IP, latency, MTU and network diagnostics
Knowledge hubFortiGate
Tools, diagnostics, commands and resources to administer and troubleshoot theFortiGate and FortiOS
Knowledge hubMicrosoft 365
Microsoft 365 administration and troubleshooting: Entra ID, Exchange Online, Intune, One (2005), SharePoint, MFA and courier