Port 8891 (ddi-tcp-4, ddi-udp-4)

IANA assigns port 8891 to ddi-tcp-4, ddi-udp-4: Desktop Data TCP 3: NESS application.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference

ddi-tcp-4 TCP Desktop Data TCP 3: NESS application Fred Yao -

ddi-udp-4 UDP Desktop Data UDP 3: NESS application Fred Yao -

Linux: is anything listening on TCP 8891?

sudo ss -tlnp 'sport = :8891'

Linux: UDP 8891

sudo ss -ulnp 'sport = :8891'

Linux / macOS: which process owns the port

sudo lsof -nP -i :8891

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':8891 '

Windows (Command Prompt)

netstat -ano | findstr :8891

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 8891 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 8891

From Windows

Test-NetConnection HOST -Port 8891

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 8891

ufw

sudo ufw deny 8891/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 8891 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 8891 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 8891' -Direction Inbound -Protocol TCP -LocalPort 8891 -Action Block

ufw

sudo ufw deny 8891/udp

iptables

sudo iptables -A INPUT -p udp --dport 8891 -j DROP

nftables

sudo nft add rule inet filter input udp dport 8891 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 8891' -Direction Inbound -Protocol UDP -LocalPort 8891 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.