Network & ports
Ports, ping, traceroute and listening services.
Test a TCP port
Checks whether an arbitrary TCP port on a host is reachable.
HTTPS (443)
- Host / server
-
mail.example.comChange in the builder →
PowerShell (Windows)
Test-NetConnection Built-in
Test-NetConnection -ComputerName mail.example.com -Port 443 -InformationLevel Detailednc / ncat Add-on tool
ncat -vz mail.example.com 443Unix shell (bash)
bash /dev/tcp Built-in
timeout 5 bash -c "</dev/tcp/mail.example.com/443" && echo open || echo closednc Add-on tool
nc -vz mail.example.com 443SMTP (25)
- Host / server
-
mail.example.comChange in the builder →
PowerShell (Windows)
Test-NetConnection Built-in
Test-NetConnection -ComputerName mail.example.com -Port 25 -InformationLevel Detailednc / ncat Add-on tool
ncat -vz mail.example.com 25Unix shell (bash)
bash /dev/tcp Built-in
timeout 5 bash -c "</dev/tcp/mail.example.com/25" && echo open || echo closednc Add-on tool
nc -vz mail.example.com 25LDAPS (636)
- Host / server
-
dc01.example.comChange in the builder →
PowerShell (Windows)
Test-NetConnection Built-in
Test-NetConnection -ComputerName dc01.example.com -Port 636 -InformationLevel Detailednc / ncat Add-on tool
ncat -vz dc01.example.com 636Unix shell (bash)
bash /dev/tcp Built-in
timeout 5 bash -c "</dev/tcp/dc01.example.com/636" && echo open || echo closednc Add-on tool
nc -vz dc01.example.com 636Ping
Checks a host's basic reachability via ICMP.
- Host / server
-
mail.example.comChange in the builder →
PowerShell (Windows)
Test-Connection Built-in
Test-Connection -TargetName mail.example.com -Count 4ping Built-in
ping -n 4 mail.example.comUnix shell (bash)
ping Built-in
ping -c 4 mail.example.comfping Add-on tool
fping -c 4 mail.example.comTraceroute
Shows the network path to a host hop by hop.
- Host / server
-
mail.example.comChange in the builder →
PowerShell (Windows)
Test-NetConnection Built-in
Test-NetConnection -ComputerName mail.example.com -TraceRoutetracert Built-in
tracert -d mail.example.comUnix shell (bash)
tracepath Built-in
tracepath mail.example.comtraceroute / mtr Add-on tool
traceroute mail.example.com
mtr -rw -c 10 mail.example.comtraceroute is not always installed on lean Linux servers. mtr gives a continuously updated view.
Who listens on a port?
Shows which process is listening locally on a port.
SMTP (25)
PowerShell (Windows)
Get-NetTCPConnection Built-in
Get-NetTCPConnection -State Listen -LocalPort 25 | Select-Object LocalAddress, LocalPort, OwningProcess
Get-Process -Id (Get-NetTCPConnection -State Listen -LocalPort 25).OwningProcessnetstat Built-in
netstat -ano | findstr ":25 "Unix shell (bash)
ss Built-in
ss -tlnp "sport = :25"lsof / netstat Add-on tool
lsof -iTCP:25 -sTCP:LISTEN
netstat -tlnp | grep ":25 "Submission (587)
PowerShell (Windows)
Get-NetTCPConnection Built-in
Get-NetTCPConnection -State Listen -LocalPort 587 | Select-Object LocalAddress, LocalPort, OwningProcess
Get-Process -Id (Get-NetTCPConnection -State Listen -LocalPort 587).OwningProcessnetstat Built-in
netstat -ano | findstr ":587 "Unix shell (bash)
ss Built-in
ss -tlnp "sport = :587"lsof / netstat Add-on tool
lsof -iTCP:587 -sTCP:LISTEN
netstat -tlnp | grep ":587 "Which DNS server?
Shows which DNS servers the system currently uses: important with split DNS.
PowerShell (Windows)
Get-DnsClientServerAddress Built-in
Get-DnsClientServerAddress -AddressFamily IPv4 | Select-Object InterfaceAlias, ServerAddressesipconfig Built-in
ipconfig /allUnix shell (bash)
resolvectl Built-in
resolvectl statuscat Built-in
cat /etc/resolv.conf