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Port 681 (entrust-aams)

IANA assigns port 681 to entrust-aams.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
entrust-aams TCP entrust-aams Adrian Mancini -
entrust-aams UDP entrust-aams Adrian Mancini -

Check what is listening on port 681

Linux: is anything listening on TCP 681?
sudo ss -tlnp 'sport = :681'
Linux: UDP 681
sudo ss -ulnp 'sport = :681'
Linux / macOS: which process owns the port
sudo lsof -nP -i :681
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':681 '
Windows (Command Prompt)
netstat -ano | findstr :681
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 681 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 681
From Windows
Test-NetConnection HOST -Port 681
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 681

Block port 681 in the firewall

ufw
sudo ufw deny 681/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 681 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 681 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 681' -Direction Inbound -Protocol TCP -LocalPort 681 -Action Block
ufw
sudo ufw deny 681/udp
iptables
sudo iptables -A INPUT -p udp --dport 681 -j DROP
nftables
sudo nft add rule inet filter input udp dport 681 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 681' -Direction Inbound -Protocol UDP -LocalPort 681 -Action Block

Related ports

679mrm680entrust-aaas682xfr683corba-iiop

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