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Port 256 (rap)

IANA assigns port 256 to rap: RAP.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
rap TCP RAP J S Greenfield -
rap UDP RAP J S Greenfield -

Check what is listening on port 256

Linux: is anything listening on TCP 256?
sudo ss -tlnp 'sport = :256'
Linux: UDP 256
sudo ss -ulnp 'sport = :256'
Linux / macOS: which process owns the port
sudo lsof -nP -i :256
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':256 '
Windows (Command Prompt)
netstat -ano | findstr :256
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 256 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 256
From Windows
Test-NetConnection HOST -Port 256
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 256

Block port 256 in the firewall

ufw
sudo ufw deny 256/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 256 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 256 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 256' -Direction Inbound -Protocol TCP -LocalPort 256 -Action Block
ufw
sudo ufw deny 256/udp
iptables
sudo iptables -A INPUT -p udp --dport 256 -j DROP
nftables
sudo nft add rule inet filter input udp dport 256 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 256' -Direction Inbound -Protocol UDP -LocalPort 256 -Action Block

Related ports

38rap247subntbcst-tftp, subntbcst_tftp248bhfhs257set259esro-gen

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