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Port 353 (ndsauth)

IANA assigns port 353 to ndsauth: NDSAUTH.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
ndsauth TCP NDSAUTH Jayakumar Ramalingam -
ndsauth UDP NDSAUTH Jayakumar Ramalingam -

Check what is listening on port 353

Linux: is anything listening on TCP 353?
sudo ss -tlnp 'sport = :353'
Linux: UDP 353
sudo ss -ulnp 'sport = :353'
Linux / macOS: which process owns the port
sudo lsof -nP -i :353
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':353 '
Windows (Command Prompt)
netstat -ano | findstr :353
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 353 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 353
From Windows
Test-NetConnection HOST -Port 353
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 353

Block port 353 in the firewall

ufw
sudo ufw deny 353/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 353 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 353 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 353' -Direction Inbound -Protocol TCP -LocalPort 353 -Action Block
ufw
sudo ufw deny 353/udp
iptables
sudo iptables -A INPUT -p udp --dport 353 -j DROP
nftables
sudo nft add rule inet filter input udp dport 353 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 353' -Direction Inbound -Protocol UDP -LocalPort 353 -Action Block

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