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Port 2138 (unbind-cluster)

IANA assigns port 2138 to unbind-cluster: UNBIND-CLUSTER.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
unbind-cluster TCP UNBIND-CLUSTER Francois Harvey -
unbind-cluster UDP UNBIND-CLUSTER Francois Harvey -

Check what is listening on port 2138

Linux: is anything listening on TCP 2138?
sudo ss -tlnp 'sport = :2138'
Linux: UDP 2138
sudo ss -ulnp 'sport = :2138'
Linux / macOS: which process owns the port
sudo lsof -nP -i :2138
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':2138 '
Windows (Command Prompt)
netstat -ano | findstr :2138
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 2138 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 2138
From Windows
Test-NetConnection HOST -Port 2138
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 2138

Block port 2138 in the firewall

ufw
sudo ufw deny 2138/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 2138 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 2138 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 2138' -Direction Inbound -Protocol TCP -LocalPort 2138 -Action Block
ufw
sudo ufw deny 2138/udp
iptables
sudo iptables -A INPUT -p udp --dport 2138 -j DROP
nftables
sudo nft add rule inet filter input udp dport 2138 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 2138' -Direction Inbound -Protocol UDP -LocalPort 2138 -Action Block

Related ports

2136appworxsrv2137connect2139ias-auth2140ias-reg

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