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Port 636 (LDAPS)

LDAP over implicit TLS.

Well-known (system) port, 0-1023 TCP Directory and authentication Do not expose to the internet

What port 636 is used for

LDAP over implicit TLS.

Security: should port 636 be open?

Do not expose to the internet. Encrypted, but still a directory full of user data: allow only the applications that authenticate against it.

IANA assignment

Service nameProtoDescriptionAssigneeReference
ldaps TCP ldap protocol over TLS/SSL (was sldap) Pat Richard -
ldaps UDP ldap protocol over TLS/SSL (was sldap) Pat Richard -

Check what is listening on port 636

Linux: is anything listening on TCP 636?
sudo ss -tlnp 'sport = :636'
Linux / macOS: which process owns the port
sudo lsof -nP -i :636
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':636 '
Windows (Command Prompt)
netstat -ano | findstr :636
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 636 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 636
From Windows
Test-NetConnection HOST -Port 636

Block port 636 in the firewall

ufw
sudo ufw deny 636/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 636 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 636 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 636' -Direction Inbound -Protocol TCP -LocalPort 636 -Action Block

Related ports

389LDAP3269AD Global Catalog over TLS88Kerberos634ginad635rlzdbase637lanserver638mcns-sec

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.