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Port 90 (dnsix)

IANA assigns port 90 to dnsix: DNSIX Securit Attribute Token Map.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
dnsix TCP DNSIX Securit Attribute Token Map Charles Watt -
dnsix UDP DNSIX Securit Attribute Token Map Charles Watt -

Check what is listening on port 90

Linux: is anything listening on TCP 90?
sudo ss -tlnp 'sport = :90'
Linux: UDP 90
sudo ss -ulnp 'sport = :90'
Linux / macOS: which process owns the port
sudo lsof -nP -i :90
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':90 '
Windows (Command Prompt)
netstat -ano | findstr :90
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 90 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 90
From Windows
Test-NetConnection HOST -Port 90
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 90

Block port 90 in the firewall

ufw
sudo ufw deny 90/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 90 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 90 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 90' -Direction Inbound -Protocol TCP -LocalPort 90 -Action Block
ufw
sudo ufw deny 90/udp
iptables
sudo iptables -A INPUT -p udp --dport 90 -j DROP
nftables
sudo nft add rule inet filter input udp dport 90 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 90' -Direction Inbound -Protocol UDP -LocalPort 90 -Action Block

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