Port 257 (set)

IANA assigns port 257 to set: Secure Electronic Transaction.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference

set TCP Secure Electronic Transaction Donald Eastlake -

set UDP Secure Electronic Transaction Donald Eastlake -

Linux: is anything listening on TCP 257?

sudo ss -tlnp 'sport = :257'

Linux: UDP 257

sudo ss -ulnp 'sport = :257'

Linux / macOS: which process owns the port

sudo lsof -nP -i :257

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':257 '

Windows (Command Prompt)

netstat -ano | findstr :257

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 257 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 257

From Windows

Test-NetConnection HOST -Port 257

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

nc -vzu -w 5 HOST 257

ufw

sudo ufw deny 257/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 257 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 257 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 257' -Direction Inbound -Protocol TCP -LocalPort 257 -Action Block

ufw

sudo ufw deny 257/udp

iptables

sudo iptables -A INPUT -p udp --dport 257 -j DROP

nftables

sudo nft add rule inet filter input udp dport 257 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 257' -Direction Inbound -Protocol UDP -LocalPort 257 -Action Block

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