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Port 87 (any private terminal link)

IANA assigns port 87 to any private terminal link.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
- TCP any private terminal link Jon Postel -
- UDP any private terminal link Jon Postel -

Check what is listening on port 87

Linux: is anything listening on TCP 87?
sudo ss -tlnp 'sport = :87'
Linux: UDP 87
sudo ss -ulnp 'sport = :87'
Linux / macOS: which process owns the port
sudo lsof -nP -i :87
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':87 '
Windows (Command Prompt)
netstat -ano | findstr :87
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 87 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 87
From Windows
Test-NetConnection HOST -Port 87
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 87

Block port 87 in the firewall

ufw
sudo ufw deny 87/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 87 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 87 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 87' -Direction Inbound -Protocol TCP -LocalPort 87 -Action Block
ufw
sudo ufw deny 87/udp
iptables
sudo iptables -A INPUT -p udp --dport 87 -j DROP
nftables
sudo nft add rule inet filter input udp dport 87 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 87' -Direction Inbound -Protocol UDP -LocalPort 87 -Action Block

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