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Port 1638 (ismc)

IANA assigns port 1638 to ismc: ISP shared management control.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
ismc TCP ISP shared management control Nick Austin -
ismc UDP ISP shared management control Nick Austin -

Check what is listening on port 1638

Linux: is anything listening on TCP 1638?
sudo ss -tlnp 'sport = :1638'
Linux: UDP 1638
sudo ss -ulnp 'sport = :1638'
Linux / macOS: which process owns the port
sudo lsof -nP -i :1638
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':1638 '
Windows (Command Prompt)
netstat -ano | findstr :1638
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1638 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 1638
From Windows
Test-NetConnection HOST -Port 1638
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 1638

Block port 1638 in the firewall

ufw
sudo ufw deny 1638/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 1638 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 1638 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 1638' -Direction Inbound -Protocol TCP -LocalPort 1638 -Action Block
ufw
sudo ufw deny 1638/udp
iptables
sudo iptables -A INPUT -p udp --dport 1638 -j DROP
nftables
sudo nft add rule inet filter input udp dport 1638 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 1638' -Direction Inbound -Protocol UDP -LocalPort 1638 -Action Block

Related ports

1636isdc1637islc1639cert-initiator1640cert-responder

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