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Port 1021 (exp1)

IANA assigns port 1021 to exp1: RFC3692-style Experiment 1.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
exp1 TCP RFC3692-style Experiment 1 IESG 1, RFC 4727, RFC 6335
exp1 UDP RFC3692-style Experiment 1 IESG 1, RFC 4727, RFC 6335
exp1 SCTP RFC3692-style Experiment 1 IESG 1, RFC 4727, RFC 6335
exp1 DCCP RFC3692-style Experiment 1 IESG 1, RFC 4727, RFC 6335

Check what is listening on port 1021

Linux: is anything listening on TCP 1021?
sudo ss -tlnp 'sport = :1021'
Linux: UDP 1021
sudo ss -ulnp 'sport = :1021'
Linux / macOS: which process owns the port
sudo lsof -nP -i :1021
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':1021 '
Windows (Command Prompt)
netstat -ano | findstr :1021
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1021 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 1021
From Windows
Test-NetConnection HOST -Port 1021
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 1021

Block port 1021 in the firewall

ufw
sudo ufw deny 1021/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 1021 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 1021 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 1021' -Direction Inbound -Protocol TCP -LocalPort 1021 -Action Block
ufw
sudo ufw deny 1021/udp
iptables
sudo iptables -A INPUT -p udp --dport 1021 -j DROP
nftables
sudo nft add rule inet filter input udp dport 1021 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 1021' -Direction Inbound -Protocol UDP -LocalPort 1021 -Action Block

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